Call a function in a shared library: Difference between revisions
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Revision as of 04:28, 27 October 2021
You are encouraged to solve this task according to the task description, using any language you may know.
Show how to call a function in a shared library (without dynamically linking to it at compile-time). In particular, show how to call the shared library function if the library is available, otherwise use an internal equivalent function.
This is a special case of calling a foreign language function where the focus is close to the ABI level and not at the normal API level.
- Related task
- OpenGL -- OpenGL is usually maintained as a shared library.
Ada
Windows
The following solution calls MessageBox from Windows' dynamic library user32.dll. It does not use Win32 bindings, which would be meaningless, because MessageBox is already there. Instead of that it links statically to kernel32.dll, which required to load anything under Windows. From there it uses LoadLibrary to load user32.dll and then GetProcAddress to get the MessageBox entry point there. Note how Windows mangles names of functions in the import libraries. So "LoadLibrary" becomes "_LoadLibraryA@4", which is its real name. "A" means ASCII. Once address of MessageBox is obtained it is converted to a pointer to a function that has an interface corresponding to it. Note Windows' call convention, which is stdcall. <lang Ada>with Ada.Text_IO; use Ada.Text_IO; with Interfaces; use Interfaces; with Interfaces.C; use Interfaces.C; with System; use System;
with Ada.Unchecked_Conversion;
procedure Shared_Library_Call is
-- -- Interface to kernel32.dll which is responsible for loading DLLs under Windows. -- There are ready to use Win32 bindings. We don't want to use them here. -- type HANDLE is new Unsigned_32; -- on x64 system, replace by Unsigned_64 to make it work function LoadLibrary (lpFileName : char_array) return HANDLE; pragma Import (stdcall, LoadLibrary, "LoadLibrary", "_LoadLibraryA"); -- Ada95 does not have the @n suffix.
function GetProcAddress (hModule : HANDLE; lpProcName : char_array)
return Address;
pragma Import (stdcall, GetProcAddress, "GetProcAddress", "_GetProcAddress"); --
--
-- The interface of the function we want to call. It is a pointer (access type)
-- because we will link it dynamically. The function is from User32.dll
--
type MessageBox is access function
( hWnd : Address := Null_Address;
lpText : char_array;
lpCaption : char_array := To_C ("Greeting");
uType : Unsigned_16 := 0
) return Integer_16;
pragma Convention (Stdcall, MessageBox);
function To_MessageBox is new Ada.Unchecked_Conversion (Address, MessageBox);
Library : HANDLE := LoadLibrary (To_C ("user32.dll"));
Pointer : Address := GetProcAddress (Library, To_C ("MessageBoxA"));
begin
if Pointer /= Null_Address then
declare
Result : Integer_16;
begin
Result := To_MessageBox (Pointer) (lpText => To_C ("Hello!"));
end;
else
Put_Line ("Unable to load the library " & HANDLE'Image (Library));
end if;
end Shared_Library_Call;</lang>
Linux
Here we are using the dl library statically (-ldl switch upon linking) and Xlib dynamically (libX11.so). The function dlopen loads a library. The function dlsym looks up for an entry point there. From libX11.so, first XOpenDisplay is called to open an X11 display, which name is in the DISPLAY environment variable. Then XDisplayWidth of the display is obtained an printed into the standard output. <lang Ada>with Ada.Environment_Variables; use Ada.Environment_Variables; with Ada.Text_IO; use Ada.Text_IO; with Interfaces; use Interfaces; with Interfaces.C; use Interfaces.C; with System; use System;
with Ada.Unchecked_Conversion;
procedure Shared_Library_Call is
-- -- Interface to libdl to load dynamically linked libraries -- function dlopen (FileName : char_array; Flag : int) return Address; pragma Import (C, dlopen);
function dlsym (Handle : address; Symbol : char_array) return Address; pragma Import (C, dlsym); -- -- The interfaces of the functions we want to call. These are pointers -- (access type) because we will link it dynamically. The functions -- come from libX11.so. -- type XOpenDisplay is access function (Display_Name : char_array) return Address; pragma Convention (C, XOpenDisplay); function To_Ptr is new Ada.Unchecked_Conversion (Address, XOpenDisplay);
type XDisplayWidth is access function (Display : Address; Screen : int) return int; pragma Convention (C, XDisplayWidth); function To_Ptr is new Ada.Unchecked_Conversion (Address, XDisplayWidth);
Library : Address := dlopen (To_C ("libX11.so"), 1);
OpenDisplay : XOpenDisplay := To_Ptr (dlsym (Library, To_C ("XOpenDisplay")));
DisplayWidth : XDisplayWidth := To_Ptr (dlsym (Library, To_C ("XDisplayWidth")));
begin
if OpenDisplay /= null and then DisplayWidth /= null then
declare
Display : Address;
begin
Display := OpenDisplay (To_C (Value ("DISPLAY")));
if Display = Null_Address then
Put_Line ("Unable to open display " & Value ("DISPLAY"));
else
Put_Line (Value ("DISPLAY") & " width is" & int'image (DisplayWidth (Display, 0)));
end if;
end;
else
Put_Line ("Unable to load the library");
end if;
end Shared_Library_Call;</lang>
Arturo
<lang rebol>getCurlVersion: function [][
try? [
call.external:'curl "curl_version" .expect: :string []
]
else [
"library not found"
]
]
print ["curl version:" getCurlVersion]</lang>
- Output:
curl version: libcurl/7.64.1 SecureTransport (LibreSSL/2.8.3) zlib/1.2.11 nghttp2/1.41.0
AutoHotkey
dllhost.ahk <lang AutoHotkey>ahkdll := DllCall("LoadLibrary", "str", "AutoHotkey.dll") clientHandle := DllCall("AutoHotkey\ahkdll", "str", "dllclient.ahk", "str" , "", "str", "parameter1 parameter2", "Cdecl Int")</lang> dllclient.ahk <lang AutoHotkey>Msgbox, hello from client</lang>
BaCon
<lang qbasic>' Call a dynamic library function PROTO j0 bessel0 = j0(1.0) PRINT bessel0 </lang>
- Output:
prompt$ bacon calllib.bac Converting 'calllib.bac'... done, 4 lines were processed in 0.004 seconds. Compiling 'calllib.bac'... cc -c calllib.bac.c cc -o calllib calllib.bac.o -lbacon -lm Done, program 'calllib' ready. prompt$ ./calllib 0.765198
BBC BASIC
The following shared libraries are automatically available: ADVAPI32.DLL, COMCTL32.DLL, COMDLG32.DLL, GDI32.DLL, KERNEL32.DLL, SHELL32.DLL, USER32.DLL and WINMM.DLL. <lang bbcbasic> SYS "MessageBox", @hwnd%, "This is a test message", 0, 0 </lang>
C
Tested with gcc on a GNU/Linux system (on GNU/Linux dl* functions are available linking to libdl, i.e. with -ldl option)
<lang c>#include <stdio.h>
- include <stdlib.h>
- include <dlfcn.h>
int myopenimage(const char *in) {
static int handle=0; fprintf(stderr, "internal openimage opens %s...\n", in); return handle++;
}
int main() {
void *imglib; int (*extopenimage)(const char *); int imghandle;
imglib = dlopen("./fakeimglib.so", RTLD_LAZY);
if ( imglib != NULL ) {
/* extopenimage = (int (*)(const char *))dlsym(imglib,...)
"man dlopen" says that C99 standard leaves casting from
"void *" to a function pointer undefined. The following is the
POSIX.1-2003 workaround found in man */
*(void **)(&extopenimage) = dlsym(imglib, "openimage");
/* the following works with gcc, gives no warning even with
-Wall -std=c99 -pedantic options... :D */
/* extopenimage = dlsym(imglib, "openimage"); */
imghandle = extopenimage("fake.img");
} else {
imghandle = myopenimage("fake.img");
}
printf("opened with handle %d\n", imghandle);
/* ... */
if (imglib != NULL ) dlclose(imglib);
return EXIT_SUCCESS;
}</lang>
The fake fakeimglib.so code is
<lang c>#include <stdio.h> /* gcc -shared -nostartfiles fakeimglib.c -o fakeimglib.so */ int openimage(const char *s) {
static int handle = 100; fprintf(stderr, "opening %s\n", s); return handle++;
}</lang>
When the library fakeimglib.so exists in the current directory (this choice is senseful only for testing purposes), the output is:
opening fake.img opened with handle 100
otherwise the output is:
internal openimage opens fake.img... opened with handle 0
C#
In Windows. <lang csharp>using System.Runtime.InteropServices;
class Program {
[DllImport("fakelib.dll")]
public static extern int fakefunction(int args);
static void Main(string[] args) {
int r = fakefunction(10);
}
}</lang>
COBOL
Tested with GnuCOBOL, GNU/Linux.
<lang cobol> identification division.
program-id. callsym.
data division.
working-storage section.
01 handle usage pointer.
01 addr usage program-pointer.
procedure division.
call "dlopen" using
by reference null
by value 1
returning handle
on exception
display function exception-statement upon syserr
goback
end-call
if handle equal null then
display function module-id ": error getting dlopen handle"
upon syserr
goback
end-if
call "dlsym" using
by value handle
by content z"perror"
returning addr
end-call
if addr equal null then
display function module-id ": error getting perror symbol"
upon syserr
else
call addr returning omitted
end-if
goback.
end program callsym.</lang>
- Output:
prompt$ cobc -xj callsym.cob Success
Common Lisp
<lang lisp>CL-USER> (cffi:load-foreign-library "libX11.so")
- <CFFI::FOREIGN-LIBRARY {1004F4ECC1}>
CL-USER> (cffi:foreign-funcall "XOpenDisplay"
:string #+sbcl (sb-posix:getenv "DISPLAY")
#-sbcl ":0.0"
:pointer)
- .(SB-SYS:INT-SAP #X00650FD0)</lang>
Crystal
<lang ruby>libm = LibC.dlopen("libm.so.6", LibC::RTLD_LAZY) sqrtptr = LibC.dlsym(libm, "sqrt") unless libm.null?
if sqrtptr
sqrtproc = Proc(Float64, Float64).new sqrtptr, Pointer(Void).null
at_exit { LibC.dlclose(libm) }
else
sqrtproc = ->Math.sqrt(Float64)
end
puts "the sqrt of 4 is #{sqrtproc.call(4.0)}"</lang>
D
<lang d>pragma(lib, "user32.lib");
import std.stdio, std.c.windows.windows;
extern(Windows) UINT GetDoubleClickTime();
void main() {
writeln(GetDoubleClickTime());
}</lang>
500
Dart
add.c <lang c> int add(int num1, int num2) { return num1 + num2; } </lang>
Dart code <lang javascript>import 'dart:ffi' show DynamicLibrary, NativeFunction, Int32;
main(){ final lib = DynamicLibrary.open('add.dylib'); // Load library
final int Function(int num1,int num2) add = lib // Write Dart function binding .lookup<NativeFunction<Int32 Function( Int32, Int32 )>>('add') // Lookup function in library .asFunction(); // convert to Dart Function
print( add( 1, 2 ) ); } </lang>
Delphi
Static loading
Loads library on startup.
<lang Delphi>procedure DoSomething; external 'MYLIB.DLL';</lang>
Delayed loading
Loads library on first call to DoSomething.
<lang Delphi>procedure DoSomething; external 'MYLIB.DLL' delayed;</lang>
Dynamic loading
Loads and unloads library on demand.
<lang Delphi>var
lLibraryHandle: THandle; lDoSomething: procedure; stdcall;
begin
lLibraryHandle := LoadLibrary('MYLIB.DLL');
if lLibraryHandle >= 32 then { success }
begin
lDoSomething := GetProcAddress(lLibraryHandle, 'DoSomething');
lDoSomething();
FreeLibrary(lLibraryHandle);
end;
end;</lang>
Forth
GNU Forth 0.7.9 on Linux
Call tgamma() from limbm.so <lang Forth> c-library math
s" m" add-lib \c #include <math.h> c-function gamma tgamma r -- r
end-c-library </lang>
- Output:
require ./foreign.fs ok 1.01e2 gamma fs. 9.33262154439442E157 ok
Fortran
GNU Fortran on Linux
Works on Linux with GNU gcc and gfortran 5.1.1
This is a slightly modified version of Call a foreign-language function task.
A simple "C" function add_n in add_n.c <lang c> double add_n(double* a, double* b) { return *a + *b; }
</lang>
compile it
gcc -c -shared -fPIC add_n.c
We can also use fortran function in the shared library which should be, however, implemented using C interoperability module.
File add_nf.f90 <lang fortran> function add_nf(a,b) bind(c, name='add_nf') use, intrinsic :: iso_c_binding implicit none real(c_double), intent(in) :: a,b real(c_double) :: add_nf
add_nf = a + b end function add_nf
</lang>
Compile it
gfortran -c -shared -fPIC add_nf.f90
create shared library shared_lib_new.so containing two functions "add_n" and "add_nf"
gcc -shared -fPIC add_nf.o add_n.o -o shared_lib_new.so
Using C binding load shared_lib_new.so and call functions add_n, add_nf dynamically.
File shared_lib_new_test.f90 <lang fortran> !----------------------------------------------------------------------- !module dll_module !----------------------------------------------------------------------- module dll_module
use iso_c_binding implicit none private ! all by default public :: os_type, dll_type, load_dll, free_dll, init_os_type, init_dll ! general constants: ! the number of bits in an address (32-bit or 64-bit). integer, parameter :: bits_in_addr = c_intptr_t*8 ! global error-level variables: integer, parameter :: errid_none = 0 integer, parameter :: errid_info = 1 integer, parameter :: errid_warn = 2 integer, parameter :: errid_severe = 3 integer, parameter :: errid_fatal = 4
integer :: os_id
type os_type
character(10) :: endian
character(len=:), allocatable :: newline
character(len=:), allocatable :: os_desc
character(1) :: pathsep
character(1) :: swchar
character(11) :: unfform
end type os_type
type dll_type
integer(c_intptr_t) :: fileaddr
type(c_ptr) :: fileaddrx
type(c_funptr) :: procaddr
character(1024) :: filename
character(1024) :: procname
end type dll_type
! interface to linux API
interface
function dlopen(filename,mode) bind(c,name="dlopen")
! void *dlopen(const char *filename, int mode);
use iso_c_binding
implicit none
type(c_ptr) :: dlopen
character(c_char), intent(in) :: filename(*)
integer(c_int), value :: mode
end function
function dlsym(handle,name) bind(c,name="dlsym")
! void *dlsym(void *handle, const char *name);
use iso_c_binding
implicit none
type(c_funptr) :: dlsym
type(c_ptr), value :: handle
character(c_char), intent(in) :: name(*)
end function
function dlclose(handle) bind(c,name="dlclose")
! int dlclose(void *handle);
use iso_c_binding
implicit none
integer(c_int) :: dlclose
type(c_ptr), value :: handle
end function
end interface
contains
!-----------------------------------------------------------------------
!Subroutine init_dll
!-----------------------------------------------------------------------
subroutine init_dll(dll)
implicit none
type(dll_type), intent(inout) :: dll
dll % fileaddr = 0
dll % fileaddrx = c_null_ptr
dll % procaddr = c_null_funptr
dll % filename = " "
dll % procname = " "
end subroutine init_dll
!-----------------------------------------------------------------------
!Subroutine init_os_type
!-----------------------------------------------------------------------
subroutine init_os_type(os_id,os)
implicit none
integer, intent(in) :: os_id
type(os_type), intent(inout) :: os
select case (os_id)
case (1) ! Linux
os % endian = 'big_endian'
os % newline = achar(10)
os % os_desc = 'Linux'
os % pathsep = '/'
os % swchar = '-'
os % unfform = 'unformatted'
case (2) ! MacOS
os % endian = 'big_endian'
os % newline = achar(10)
os % os_desc = 'MacOS'
os % pathsep = '/'
os % swchar = '-'
os % unfform = 'unformatted'
case default
end select
end subroutine init_os_type
!-----------------------------------------------------------------------
!Subroutine load_dll
!-----------------------------------------------------------------------
subroutine load_dll (os, dll, errstat, errmsg )
! this subroutine is used to dynamically load a dll.
type (os_type), intent(in) :: os
type (dll_type), intent(inout) :: dll
integer, intent( out) :: errstat
character(*), intent( out) :: errmsg
integer(c_int), parameter :: rtld_lazy=1
integer(c_int), parameter :: rtld_now=2
integer(c_int), parameter :: rtld_global=256
integer(c_int), parameter :: rtld_local=0
errstat = errid_none
errmsg =
select case (os%os_desc)
case ("Linux","MacOS")
! load the dll and get the file address:
dll%fileaddrx = dlopen( trim(dll%filename)//c_null_char, rtld_lazy )
if( .not. c_associated(dll%fileaddrx) ) then
errstat = errid_fatal
write(errmsg,'(i2)') bits_in_addr
errmsg = 'the dynamic library '//trim(dll%filename)//' could not be loaded. check that the file '// &
'exists in the specified location and that it is compiled for '//trim(errmsg)//'-bit systems.'
return
end if
! get the procedure address:
dll%procaddr = dlsym( dll%fileaddrx, trim(dll%procname)//c_null_char )
if(.not. c_associated(dll%procaddr)) then
errstat = errid_fatal
errmsg = 'the procedure '//trim(dll%procname)//' in file '//trim(dll%filename)//' could not be loaded.'
return
end if
case ("Windows")
errstat = errid_fatal
errmsg = ' load_dll not implemented for '//trim(os%os_desc)
case default
errstat = errid_fatal
errmsg = ' load_dll not implemented for '//trim(os%os_desc)
end select
return
end subroutine load_dll
!----------------------------------------------------------------------- !Subroutine free_dll !----------------------------------------------------------------------- subroutine free_dll (os, dll, errstat, errmsg )
! this subroutine is used to free a dynamically loaded dll
type (os_type), intent(in) :: os
type (dll_type), intent(inout) :: dll
integer, intent( out) :: errstat
character(*), intent( out) :: errmsg
integer(c_int) :: success
errstat = errid_none
errmsg =
select case (os%os_desc)
case ("Linux","MacOS")
! close the library:
success = dlclose( dll%fileaddrx )
if ( success /= 0 ) then
errstat = errid_fatal
errmsg = 'the dynamic library could not be freed.'
return
else
errstat = errid_none
errmsg =
end if
case ("Windows")
errstat = errid_fatal
errmsg = ' free_dll not implemented for '//trim(os%os_desc)
case default
errstat = errid_fatal
errmsg = ' free_dll not implemented for '//trim(os%os_desc)
end select
return end subroutine free_dll
end module dll_module
!----------------------------------------------------------------------- !Main program !----------------------------------------------------------------------- program test_load_dll
use, intrinsic :: iso_c_binding use dll_module implicit none
! interface to our shared lib
abstract interface
function add_n(a,b)
use, intrinsic :: iso_c_binding
implicit none
real(c_double), intent(in) :: a,b
real(c_double) :: add_n
end function add_n
end interface
type(os_type) :: os type(dll_type) :: dll integer :: errstat character(1024) :: errmsg type(c_funptr) :: cfun procedure(add_n), pointer :: fproc
call init_os_type(1,os) call init_dll(dll)
dll%filename="/full_path_to/shared_lib/shared_lib_new.so" ! name of the procedure in shared_lib ! c version of the function dll%procname="add_n"
write(*,*) "address: ", dll%procaddr
call load_dll(os, dll, errstat, errmsg ) write(*,*)"load_dll: errstat=", errstat write(*,*) "address: ", dll%procaddr
call c_f_procpointer(dll%procaddr,fproc)
write(*,*) "add_n(2,5)=",fproc(2.d0,5.d0)
call free_dll (os, dll, errstat, errmsg ) write(*,*)"free_dll: errstat=", errstat
! fortran version dll%procname="add_nf"
call load_dll(os, dll, errstat, errmsg ) write(*,*)"load_dll: errstat=", errstat write(*,*) "address: ", dll%procaddr
call c_f_procpointer(dll%procaddr,fproc)
write(*,*) "add_nf(2,5)=",fproc(2.d0,5.d0)
call free_dll (os, dll, errstat, errmsg ) write(*,*)"free_dll: errstat=", errstat
end program test_load_dll
</lang> Compile test program
gfortran shared_lib_new_test.f90 -ldl -o shared_lib_new_test.x
- Output:
./shared_lib_new_test.x
address: 0 load_dll: errstat= 0 address: 47476893497132 add_n(2,5)= 7.0000000000000000 free_dll: errstat= 0 load_dll: errstat= 0 address: 47476893497088 add_nf(2,5)= 7.0000000000000000 free_dll: errstat= 0
Finally, using C language interoperability you can call every foreign-language function in fortran if you are able to write some additional wrapper function in C language.
Intel Fortran on Windows
First, the DLL. Compile with ifort /dll dllfun.f90. The function is compiled with the STDCALL calling convention: it's not necessary here but it shows how to do it. <lang fortran>function ffun(x, y)
implicit none !DEC$ ATTRIBUTES DLLEXPORT, STDCALL, REFERENCE :: FFUN double precision :: x, y, ffun ffun = x + y * y
end function</lang>
Now, the main program. It will wait for two numbers and compute the result with the DLL function. Compile with ifort dynload.f90. Three functions of the Kernel32 library are necessary, see LoadLibrary, GetProcAddress and FreeLibrary in the MSDN. The kernel32 module is provided with the Intel Fortran compiler. The DLL has to be in a directory in the PATH environment variable.
<lang fortran>program dynload
use kernel32
use iso_c_binding
implicit none
abstract interface
function ffun_int(x, y)
!DEC$ ATTRIBUTES STDCALL, REFERENCE :: ffun_int
double precision :: ffun_int, x, y
end function
end interface
procedure(ffun_int), pointer :: ffun_ptr
integer(c_intptr_t) :: ptr
integer(handle) :: h
double precision :: x, y
h = LoadLibrary("dllfun.dll" // c_null_char)
if (h == 0) error stop "Error: LoadLibrary"
ptr = GetProcAddress(h, "ffun" // c_null_char)
if (ptr == 0) error stop "Error: GetProcAddress"
call c_f_procpointer(transfer(ptr, c_null_funptr), ffun_ptr)
read *, x, y
print *, ffun_ptr(x, y)
if (FreeLibrary(h) == 0) error stop "Error: FreeLibrary"
end program</lang>
GNU Fortran on Windows
The program for Intel Fortran can easily be adapted to the GNU Fortran compiler. A kernel32 module must be provided (here a small version with only the three necessary functions is given). Also, the STDCALL declaration is different. The dllfun.dll library must be in the PATH, but also MinGW libraries.
To compile:
gfortran -Wall -c kernel32.f90 gfortran -Wall -shared dllfun.f90 -o dllfun.dll gfortran -Wall dynload.f90 -lkernel32
With the standard conformance option -std=f2008, GNU Fortran will complain about the c_f_procpointer call in the main program. Use -std=f2008ts instead.
First the DLL: <lang fortran>function ffun(x, y)
implicit none !GCC$ ATTRIBUTES DLLEXPORT, STDCALL :: FFUN double precision :: x, y, ffun ffun = x + y * y
end function</lang>
Main program: <lang fortran>program dynload
use kernel32
use iso_c_binding
implicit none
abstract interface
function ffun_int(x, y)
!GCC$ ATTRIBUTES DLLEXPORT, STDCALL :: FFUN
double precision :: ffun_int, x, y
end function
end interface
procedure(ffun_int), pointer :: ffun_ptr
integer(c_intptr_t) :: ptr
integer(handle) :: h
double precision :: x, y
h = LoadLibrary("dllfun.dll" // c_null_char)
if (h == 0) error stop "Error: LoadLibrary"
ptr = GetProcAddress(h, "ffun_@8" // c_null_char)
if (ptr == 0) error stop "Error: GetProcAddress"
call c_f_procpointer(transfer(ptr, c_null_funptr), ffun_ptr)
read *, x, y
print *, ffun_ptr(x, y)
if (FreeLibrary(h) == 0) error stop "Error: FreeLibrary"
end program</lang>
Interface module: <lang fortran>module kernel32
use iso_c_binding
implicit none
integer, parameter :: HANDLE = C_INTPTR_T
integer, parameter :: PVOID = C_INTPTR_T
integer, parameter :: BOOL = C_INT
interface
function LoadLibrary(lpFileName) bind(C, name="LoadLibraryA")
import C_CHAR, HANDLE
!GCC$ ATTRIBUTES STDCALL :: LoadLibrary
integer(HANDLE) :: LoadLibrary
character(C_CHAR) :: lpFileName
end function
end interface
interface
function FreeLibrary(hModule) bind(C, name="FreeLibrary")
import HANDLE, BOOL
!GCC$ ATTRIBUTES STDCALL :: FreeLibrary
integer(BOOL) :: FreeLibrary
integer(HANDLE), value :: hModule
end function
end interface
interface
function GetProcAddress(hModule, lpProcName) bind(C, name="GetProcAddress")
import C_CHAR, PVOID, HANDLE
!GCC$ ATTRIBUTES STDCALL :: GetProcAddress
integer(PVOID) :: GetProcAddress
integer(HANDLE), value :: hModule
character(C_CHAR) :: lpProcName
end function
end interface
end module</lang>
FreeBASIC
<lang freebasic>' FB 1.05.0 Win64
' Attempt to call Beep function in Win32 API Dim As Any Ptr library = DyLibLoad("kernel32.dll") load dll
If library = 0 Then
Print "Unable to load kernel32.dll - calling built in Beep function instead" Beep : Beep : Beep
Else
Dim beep_ As Function (ByVal As ULong, ByVal As ULong) As Long declare function pointer beep_ = DyLibSymbol(library, "Beep") If beep_ = 0 Then Print "Unable to retrieve Beep function from kernel32.dll - calling built in Beep function instead" Beep : Beep : Beep Else For i As Integer = 1 To 3 : beep_(1000, 250) : Next End If DyLibFree(library) unload library
End If
Print Print "Press any key to quit" Sleep</lang>
Go
Dynamically calling a function from a shared library can only be accomplished in Go using 'cgo' and, even then, the function pointer returned by 'dlsym' can only be called via a C bridging function as calling C function pointers directly from Go is not currently supported.
This is the C code to produce fakeimglib.so: <lang c>#include <stdio.h> /* gcc -shared -fPIC -nostartfiles fakeimglib.c -o fakeimglib.so */ int openimage(const char *s) {
static int handle = 100; fprintf(stderr, "opening %s\n", s); return handle++;
}</lang> And this is the Go code to dynamically load the .so file and call the 'openimage' function - or if the .so file (or the function itself) is not available, to call the internal version of the function: <lang go>package main
/*
- cgo LDFLAGS: -ldl
- include <stdlib.h>
- include <dlfcn.h>
typedef int (*someFunc) (const char *s);
int bridge_someFunc(someFunc f, const char *s) {
return f(s);
}
- /
import "C" import (
"fmt" "os" "unsafe"
)
var handle = -1
func myOpenImage(s string) int {
fmt.Fprintf(os.Stderr, "internal openImage opens %s...\n", s) handle++ return handle
}
func main() {
libpath := C.CString("./fakeimglib.so")
defer C.free(unsafe.Pointer(libpath))
imglib := C.dlopen(libpath, C.RTLD_LAZY)
var imghandle int
if imglib != nil {
openimage := C.CString("openimage")
defer C.free(unsafe.Pointer(openimage))
fp := C.dlsym(imglib, openimage)
if fp != nil {
fi := C.CString("fake.img")
defer C.free(unsafe.Pointer(fi))
imghandle = int(C.bridge_someFunc(C.someFunc(fp), fi))
} else {
imghandle = myOpenImage("fake.img")
}
C.dlclose(imglib)
} else {
imghandle = myOpenImage("fake.img")
}
fmt.Printf("opened with handle %d\n", imghandle)
}</lang>
- Output:
Same as C entry.
Haskell
<lang haskell>#!/usr/bin/env stack -- stack --resolver lts-6.33 --install-ghc runghc --package unix
import Control.Exception ( try ) import Foreign ( FunPtr, allocaBytes ) import Foreign.C
( CSize(..), CString, withCAStringLen, peekCAStringLen )
import System.Info ( os ) import System.IO.Error ( ioeGetErrorString ) import System.IO.Unsafe ( unsafePerformIO ) import System.Posix.DynamicLinker
( RTLDFlags(RTLD_LAZY), dlsym, dlopen )
dlSuffix :: String dlSuffix = if os == "darwin" then ".dylib" else ".so"
type RevFun = CString -> CString -> CSize -> IO ()
foreign import ccall "dynamic"
mkFun :: FunPtr RevFun -> RevFun
callRevFun :: RevFun -> String -> String callRevFun f s = unsafePerformIO $ withCAStringLen s $ \(cs, len) -> do
allocaBytes len $ \buf -> do f buf cs (fromIntegral len) peekCAStringLen (buf, len)
getReverse :: IO (String -> String) getReverse = do
lib <- dlopen ("libcrypto" ++ dlSuffix) [RTLD_LAZY]
fun <- dlsym lib "BUF_reverse"
return $ callRevFun $ mkFun fun
main = do
x <- try getReverse
let (msg, rev) =
case x of
Left e -> (ioeGetErrorString e ++ "; using fallback", reverse)
Right f -> ("Using BUF_reverse from OpenSSL", f)
putStrLn msg
putStrLn $ rev "a man a plan a canal panama"</lang>
J
Most of this was borrowed from Call a foreign-language function#J <lang J>require 'dll' strdup=: 'msvcrt.dll _strdup >x *' cd < free=: 'msvcrt.dll free n x' cd < getstr=: free ] memr@,&0 _1
DupStr=:verb define
try. getstr@strdup y catch. y end.
)</lang>
You get a domain error when the required library is not present at run time. A try/catch will let you handle this (as would the :: adverse operator).
Example use: <lang J> DupStr 'hello' hello
getstr@strdup ::] 'hello'
hello</lang>
Java
For methods with the native keyword, the library must be written to the Java Native Interface; this is not a general FFI. If the library is missing, System.loadLibrary() throws UnsatisfiedLinkError. We can continue if we catch this error and then don't call the library's native methods.
If you have Unix make, then edit the Makefile, run make, run java -Djava.library.path=. RSort. If you don't set java.library.path, or don't build the library, then the Java code falls back from using C to using Java. For more info about building a JNI library, see Call a foreign-language function#Java.
<lang java>/* TrySort.java */
import java.util.Collections; import java.util.Random;
public class TrySort {
static boolean useC;
static {
try { System.loadLibrary("TrySort"); useC = true; } catch(UnsatisfiedLinkError e) { useC = false; }
}
static native void sortInC(int[] ary);
static class IntList extends java.util.AbstractList<Integer> {
int[] ary; IntList(int[] ary) { this.ary = ary; } public Integer get(int i) { return ary[i]; } public Integer set(int i, Integer j) { Integer o = ary[i]; ary[i] = j; return o; } public int size() { return ary.length; }
}
static class ReverseAbsCmp
implements java.util.Comparator<Integer>
{
public int compare(Integer pa, Integer pb) { /* Order from highest to lowest absolute value. */ int a = pa > 0 ? -pa : pa; int b = pb > 0 ? -pb : pb; return a < b ? -1 : a > b ? 1 : 0; }
}
static void sortInJava(int[] ary) {
Collections.sort(new IntList(ary), new ReverseAbsCmp());
}
public static void main(String[] args) {
/* Create an array of random integers. */ int[] ary = new int[1000000]; Random rng = new Random(); for (int i = 0; i < ary.length; i++) ary[i] = rng.nextInt();
/* Do the reverse sort. */ if (useC) { System.out.print("Sorting in C... "); sortInC(ary); } else { System.out.print ("Missing library for C! Sorting in Java... "); sortInJava(ary); }
for (int i = 0; i < ary.length - 1; i++) { int a = ary[i]; int b = ary[i + 1]; if ((a > 0 ? -a : a) > (b > 0 ? -b : b)) { System.out.println("*BUG IN SORT*"); System.exit(1); } } System.out.println("ok");
}
}</lang>
<lang c>/* TrySort.c */
- include <stdlib.h>
- include "TrySort.h"
static void fail(JNIEnv *jenv, const char *error_name) {
jclass error_class = (*jenv)->FindClass(jenv, error_name); (*jenv)->ThrowNew(jenv, error_class, NULL);
}
static int reverse_abs_cmp(const void *pa, const void *pb) {
jint a = *(jint *)pa; jint b = *(jint *)pb; a = a > 0 ? -a : a; b = b > 0 ? -b : b; return a < b ? -1 : a > b ? 1 : 0;
}
void Java_TrySort_sortInC(JNIEnv *jenv, jclass obj, jintArray ary) {
jint *elem, length;
if (ary == NULL) {
fail(jenv, "java/lang/NullPointerException"); return;
}
length = (*jenv)->GetArrayLength(jenv, ary);
elem = (*jenv)->GetPrimitiveArrayCritical(jenv, ary, NULL);
if (elem == NULL) {
fail(jenv, "java/lang/OutOfMemoryError"); return;
} qsort(elem, length, sizeof(jint), reverse_abs_cmp); (*jenv)->ReleasePrimitiveArrayCritical(jenv, ary, elem, 0);
}</lang>
<lang make># Makefile
- Edit the next lines to match your JDK.
JAVA_HOME = /usr/local/jdk-1.8.0 CPPFLAGS = -I$(JAVA_HOME)/include -I$(JAVA_HOME)/include/openbsd JAVAC = $(JAVA_HOME)/bin/javac JAVAH = $(JAVA_HOME)/bin/javah
CC = cc LDFLAGS = -shared -fPIC LIB = libTrySort.so
all: TrySort.class $(LIB)
$(LIB): TrySort.c TrySort.h $(CC) $(CPPFLAGS) $(LDFLAGS) -o $@ TrySort.c
.SUFFIXES: .class .java .h .class.h: rm -f $@ $(JAVAH) -jni -o $@ $(<:.class=) .java.class: $(JAVAC) $<
clean: rm -f TrySort.class TrySort?IntList.class \ TrySort?ReverseAbsCmp.class TrySort.h $(LIB)</lang>
JNA
<lang java>import com.sun.jna.Library; import com.sun.jna.Native;
public class LoadLibJNA{
private interface YourSharedLibraryName extends Library{
//put shared library functions here with no definition
public void sharedLibraryfunction();
}
public static void main(String[] args){
YourSharedLibraryName lib = (YourSharedLibraryName)Native.loadLibrary("sharedLibrary",//as in "sharedLibrary.dll"
YourSharedLibraryName.class);
lib.sharedLibraryFunction();
}
}</lang>
Jsish
Jsish includes a load('library.so'); function, which calls a specially crafted management function in the library, JsiInitmoduleName, where the moduleName part of the exported symbol is the name of the library loaded.
Normally, this function would register commands to the shell, but this is just a DISPLAY statement on load, and then again on unload as jsish runs down. Note the name used, "Jsi_Initbyjsi", from "byjsi.so".
<lang javascript>#!/usr/local/bin/jsish load('byjsi.so');</lang>
For example, a COBOL library generated from
<lang COBOL> identification division.
program-id. sample as "Jsi_Initbyjsi".
environment division.
configuration section.
special-names.
call-convention 0 is extern.
repository.
function all intrinsic.
data division.
linkage section.
01 jsi-interp usage pointer.
01 rel usage binary-long.
procedure division using by value jsi-interp rel.
sample-main.
if rel equal zero then
display "GnuCOBOL from jsish load of " module-source()
" and cobc -m -fimplicit-init" upon syserr
goback
end-if
display "Called again with: " jsi-interp ", " rel upon syserr
goback.
end program sample.</lang>
- Output:
prompt$ cobc -m -debug -fimplicit-init byjsi.cob prompt$ ./callcob.jsi GnuCOBOL from jsish load of byjsi.cob and cobc -m -fimplicit-init Called again with: 0x00000000013a9260, +0000000002 prompt$
Julia
Julia has the `ccall` function which follows the form: ccall((symbol, library), RetType, (ArgType1, ...), ArgVar1, ...) <lang julia>
- this example works on Windows
ccall( (:GetDoubleClickTime, "User32"), stdcall, Uint, (), )
ccall( (:clock, "libc"), Int32, ())</lang> For more information, see here [1]
Kotlin
This is the C code to produce fakeimglib.so: <lang C>#include <stdio.h> /* gcc -shared -fPIC -nostartfiles fakeimglib.c -o fakeimglib.so */ int openimage(const char *s) {
static int handle = 100; fprintf(stderr, "opening %s\n", s); return handle++;
}</lang> And this is the Kotlin code to dynamically load the .so file and call the 'openimage' function - or if the .so file (or the function itself) is not available, to call the internal version of the function: <lang scala>// Kotlin Native version 0.5
import kotlinx.cinterop.* import platform.posix.* import platform.linux.*
typealias Func = (String)-> Int
var handle = 0
fun myOpenImage(s: String): Int {
fprintf(stderr, "internal openImage opens %s...\n", s) return handle++
}
fun main(args: Array<String>) {
var imgHandle: Int
val imglib = dlopen("./fakeimglib.so", RTLD_LAZY)
if (imglib != null) {
val fp = dlsym(imglib, "openimage")
if (fp != null) {
val extOpenImage: CPointer<CFunction<Func>> = fp.reinterpret()
imgHandle = extOpenImage("fake.img")
}
else {
imgHandle = myOpenImage("fake.img")
}
dlclose(imglib)
}
else {
imgHandle = myOpenImage("fake.img")
}
println("opened with handle $imgHandle")
}</lang>
- Output:
Same as C entry
Lingo
<lang lingo>-- calculate CRC-32 checksum str = "The quick brown fox jumps over the lazy dog"
-- is shared library (in Director called "Xtra", a DLL in windows, a sharedLib in -- OS X) available? if ilk(xtra("Crypto"))=#xtra then
-- use shared library
cx = xtra("Crypto").new()
crc = cx.cx_crc32_string(str)
else
-- otherwise use (slower) pure lingo solution
crcObj = script("CRC").new()
crc = crcObj.crc32(str)
end if</lang>
Lua
There is no built-in mechanism, but several external library options exist. Here, the alien library is used to display a message box via the Win32 API. <lang lua>alien = require("alien") msgbox = alien.User32.MessageBoxA msgbox:types({ ret='long', abi='stdcall', 'long', 'string', 'string', 'long' }) retval = msgbox(0, 'Please press Yes, No or Cancel', 'The Title', 3) print(retval) --> 6, 7 or 2</lang>
Maple
<lang Maple>> cfloor := define_external( floor, s::float[8], RETURN::float[8], LIB = "libm.so" ): > cfloor( 2.3 );
2.</lang>
Mathematica/Wolfram Language
This works on windows and on linux/mac too (through Mono) <lang Mathematica>Needs["NETLink`"]; externalFloor = DefineDLLFunction["floor", "msvcrt.dll", "double", { "double" }]; externalFloor[4.2] -> 4.</lang>
Nim
Interacting with C code
<lang nim>proc openimage(s: cstring): cint {.importc, dynlib: "./fakeimglib.so".}
echo openimage("foo")
echo openimage("bar")
echo openimage("baz")</lang>
The fake fakeimglib.so code is
<lang c>#include <stdio.h>
/* gcc -shared -nostartfiles fakeimglib.c -o fakeimglib.so */
int openimage(const char *s)
{
static int handle = 100; fprintf(stderr, "opening %s\n", s); return handle++;
}</lang> Output:
opening foo 100 opening bar 101 opening baz 102
Interacting with Nim code
<lang nim>proc openimage(s: string): int {.importc, dynlib: "./libfakeimg.so".}
echo openimage("foo")
echo openimage("bar")
echo openimage("baz")</lang>
The fake libfakeimg.so code is
<lang nim># nim c --app:lib fakeimg.nim
var handle = 100
proc openimage*(s: string): int {.exportc, dynlib.} =
stderr.writeln "opening ", s result = handle inc(handle)</lang>
Output:
opening foo 100 opening bar 101 opening baz 102
OCaml
As far as I know there is no solution in OCaml standard library to load a function from a C library dynamically. So I have quickly implemented a module named Dlffi that you can find in this sub-page. It is basically a wrapper around the GNU/Linux dl* functions and the libffi.
On Windows there is FlexDLL.
Here is an example of use of this Dlffi module: <lang ocaml>open Dlffi
let get_int = function Int v -> v | _ -> failwith "get_int" let get_ptr = function Ptr v -> v | _ -> failwith "get_ptr" let get_float = function Float v -> v | _ -> failwith "get_float" let get_double = function Double v -> v | _ -> failwith "get_double" let get_string = function String v -> v | _ -> failwith "get_string"
let () =
(* load the library *) let xlib = dlopen "/usr/lib/libX11.so" [RTLD_LAZY] in (* load the functions *) let _open_display = dlsym xlib "XOpenDisplay" and _default_screen = dlsym xlib "XDefaultScreen" and _display_width = dlsym xlib "XDisplayWidth" and _display_height = dlsym xlib "XDisplayHeight" in (* wrap functions to provide a higher level interface *) let open_display ~name = get_ptr(fficall _open_display [| String name |] Return_ptr) and default_screen ~dpy = get_int(fficall _default_screen [| (Ptr dpy) |] Return_int) and display_width ~dpy ~scr = get_int(fficall _display_width [| (Ptr dpy); (Int scr) |] Return_int) and display_height ~dpy ~scr = get_int(fficall _display_height [| (Ptr dpy); (Int scr) |] Return_int) in (* use our functions *) let dpy = open_display ~name:":0" in let screen_number = default_screen ~dpy in let width = display_width ~dpy ~scr:screen_number and height = display_height ~dpy ~scr:screen_number in Printf.printf "# Screen dimensions are: %d x %d pixels\n" width height; dlclose xlib;
- </lang>
Ol
Note: "strdup" is existent shared function, "strduX" is not existent. <lang scheme> (import (otus ffi))
(define self (load-dynamic-library #f)) (define strdup (or
(self type-string "strdup" type-string)
(lambda (str)
(list->string (string->list str)))))
(define strduX (or
(self type-string "strduX" type-string)
(lambda (str)
(list->string (string->list str)))))
(print (strdup "Hello World!")) (print (strduX "Hello World!")) </lang>
- Output:
Hello World! Hello World!
OxygenBasic
<lang oxygenbasic> 'Loading a shared library at run time and calling a function.
declare MessageBox(sys hWnd, String text,caption, sys utype)
sys user32 = LoadLibrary "user32.dll"
if user32 then @Messagebox = getProcAddress user32,"MessageBoxA"
if @MessageBox then MessageBox 0,"Hello","OxygenBasic",0
'...
FreeLibrary user32 </lang>
PARI/GP
<lang parigp>install("function_name","G","gp_name","./test.gp.so");</lang> where "G" is the parser code; see section 5.7.3 in the User's Guide to the PARI library for more information.
Pascal
See Delphi
Perl
Examples for simple C library calls, but each module is capable of much more (and can work with other languages). Refer to their documentation for details.
Inline
This modules auto-builds a wrapper to the library on the first call, and subsequently uses that interface with no delay. <lang perl>use Inline
C => "DATA", ENABLE => "AUTOWRAP", LIBS => "-lm";
print 4*atan(1) . "\n";
__DATA__ __C__ double atan(double x);</lang>
- Output:
3.14159265358979
FFI
This module is smart about finding libraries, here getting atan (from 'lm') and puts (from 'libc').
<lang perl>use FFI::Platypus;
my $ffi = FFI::Platypus->new;
$ffi->lib(undef);
$ffi->attach(puts => ['string'] => 'int');
$ffi->attach(atan => ['double'] => 'double');
puts(4*atan(1));</lang>
- Output:
3.14159265358979
Phix
<lang Phix>string {libname,funcname} = iff(platform()=WINDOWS?{"user32","CharLowerA"}:{"libc","tolower"}) atom lib = open_dll(libname) integer func = define_c_func(lib,funcname,{C_INT},C_INT) if func=-1 then
?Template:Lower('A')
else
?c_func(func,{'A'}) -- ('A'==65)
end if</lang>
- Output:
97 -- (or {{97}} if func not found)
PicoLisp
This differs between the 32-bit and 64-bit versions. While the 64-bit version can interface directly to C functions (in external libraries or not), requires the 32-bit function some glue code.
32-bit version
For the 32-bit version, we need some glue code: <lang PicoLisp>(load "@lib/gcc.l")
(gcc "x11" '("-lX11") 'xOpenDisplay 'xCloseDisplay)
- include <X11/Xlib.h>
any xOpenDisplay(any ex) {
any x = evSym(cdr(ex)); // Get display name char display[bufSize(x)]; // Create a buffer for the name
bufString(x, display); // Upack the name return boxCnt((long)XOpenDisplay(display));
}
any xCloseDisplay(any ex) {
return boxCnt(XCloseDisplay((Display*)evCnt(ex, cdr(ex))));
} /**/
- With that we can open and close the display:
- (setq Display (xOpenDisplay ":0.7")) # Wrong
-> 0
- (setq Display (xOpenDisplay ":0.0")) # Correct
-> 158094320
- (xCloseDisplay Display)
-> 0</lang>
64-bit version
In the 64-bit version, we can call the library directly: <lang PicoLisp>: (setq Display (native "/usr/lib/libX11.so.6" "XOpenDisplay" 'N ":0.0")) -> 6502688
- (native "/usr/lib/libX11.so.6" "XCloseDisplay" 'I Display)
-> 0</lang>
PowerBASIC
In this example, if the library can't be found (user32), or the desired function in the library (MessageBoxA), the equivalent built-in function (MSGBOX) is at the "epicFail" label... but really, if you can't find user32.dll, you've got bigger things to worry about. <lang powerbasic>#INCLUDE "Win32API.inc"
FUNCTION PBMAIN () AS LONG
DIM hWnd AS LONG DIM msg AS ASCIIZ * 14, titl AS ASCIIZ * 8
hWnd = LoadLibrary ("user32")
msg = "Hello, world!"
titl = "Example"
IF ISTRUE (hWnd) THEN
funcAddr& = GetProcAddress (hWnd, "MessageBoxA")
IF ISTRUE (funcAddr&) THEN
ASM push 0&
tAdr& = VARPTR(titl)
ASM push tAdr&
mAdr& = VARPTR(msg)
ASM push mAdr&
ASM push 0&
CALL DWORD funcAddr&
ELSE
GOTO epicFail
END IF
ELSE
GOTO epicFail
END IF
GOTO getMeOuttaHere
epicFail:
MSGBOX msg, , titl
getMeOuttaHere:
IF ISTRUE(hWnd) THEN
tmp& = FreeLibrary (hWnd)
IF ISFALSE(tmp&) THEN MSGBOX "Error freeing library... [shrug]"
END IF
END FUNCTION</lang>
PureBasic
Older PureBasic versions normally relied on CallFunction() and CallFunctionFast() <lang Purebasic>if OpenLibrary(0, "USER32.DLL")
*MessageBox = GetFunction(0, "MessageBoxA") CallFunctionFast(*MessageBox, 0, "Body", "Title", 0) CloseLibrary(0)
endif</lang> Since versions 4 the recommended way is via the usage of Prototypes even if the old system still is supported. <lang PureBasic>Prototype.l ProtoMessageBoxW(Window.l, Body.p-unicode, Title.p-unicode, Flags.l = 0)
If OpenLibrary(0, "User32.dll")
MsgBox.ProtoMessageBoxW = GetFunction(0, "MessageBoxW") MsgBox(0, "Hello", "World") CloseLibrary(0)
EndIf</lang>
Python
ctypes
Example that call User32.dll::GetDoubleClickTime() in windows. <lang python>import ctypes
user32_dll = ctypes.cdll.LoadLibrary('User32.dll') print user32_dll.GetDoubleClickTime()</lang> Or, to call printf out of the C standard library: <lang python>>>> import ctypes >>> # libc = ctypes.cdll.msvcrt # Windows >>> # libc = ctypes.CDLL('libc.dylib') # Mac >>> libc = ctypes.CDLL('libc.so') # Linux and most other *nix >>> libc.printf(b'hi there, %s\n', b'world') hi there, world. 17</lang>
CFFI
CFFI isn't built into the stdlib, but, on the other hand, it works with other Python implementations like PyPy. It also has a variety of advantages and disadvantages over ctypes, even for simple cases like this: <lang python> >>> from cffi import FFI >>> ffi = FFI() >>> ffi.cdef(""" ... int printf(const char *format, ...); // copy-pasted from the man page ... """) >>> C = ffi.dlopen(None) # loads the entire C namespace >>> arg = ffi.new("char[]", b"world") # equivalent to C code: char arg[] = "world"; >>> C.printf(b"hi there, %s.\n", arg) # call printf hi there, world. 17</lang>
QB64
<lang vb> Declare Dynamic Library "Kernel32"
Sub SetLastError (ByVal dwErr As Long) Function GetLastError& ()
End Declare
SetLastError 20 Print GetLastError</lang>
R
This is possible in R in only a few limited ways. If the library function one wishes to call is a (C-level) R function (of type SEXP), then one may call
<lang rsplus>dyn.load("my/special/R/lib.so")
.Call("my_lib_fun", arg1, arg2)</lang>
It is also possible to use .C() and .Fortran() to call voids and subroutines respectively; here the return value(s) should be in the argument list (rather than merely modifying state). An example of this might look like
<lang rsplus>.C("my_lib_fun", arg1, arg2, ret)</lang>
The return of the .C() function is an R list.
Racket
<lang racket>#lang racket (require ffi/unsafe) (define libm (ffi-lib "libm")) ; get a handle for the C math library
- look up sqrt in the math library. if we can't find it, return the builtin sqrt
(define extern-sqrt (get-ffi-obj 'sqrt libm (_fun _double -> _double)
(lambda () sqrt)))</lang>
Output:
> (extern-sqrt 42.0) 6.48074069840786
Raku
(formerly Perl 6)
<lang perl6>use NativeCall;
sub XOpenDisplay(Str $s --> int64) is native('X11') {*} sub XCloseDisplay(int64 $i --> int32) is native('X11') {*}
if try my $d = XOpenDisplay ":0.0" {
say "ID = $d"; XCloseDisplay($d);
} else {
say "No X11 library!"; say "Use this window instead --> ⬜";
}</lang>
- Output:
ID = 94722089782960
REXX
The example is using the standard library that is supplied with Regina REXX that contains a wide range of functions.
A little extra boilerplate code was added to make sure the return codes were OK.
The dropping of functions isn't really necessary for most REXX programs. <lang rexx>/*REXX program calls a function (sysTextScreenSize) in a shared library (regUtil). */
/*Note: the REGUTIL.DLL (REGina UTILity Dynamic Link Library */
/* should be in the PATH or the current directory. */
rca= rxFuncAdd('sysLoadFuncs', "regUtil", 'sysLoadFuncs') /*add a function library. */ if rca\==0 then do /*examine the return code.*/
say 'return code' rca "from rxFuncAdd" /*tell about bad " " */
exit rca /*exit this program with RC. */
end
rcl= sysLoadFuncs() /*we can load the functions. */ if rcl\==0 then do /*examine the return code.*/
say 'return code' rcl "from sysLoadFuncs" /*tell about bad " " */
exit rcl /*exit this program with RC. */
end
/* [↓] call a function. */
$= sysTextScreenSize() /*$ has 2 words: rows cols */ parse var $ rows cols . /*get two numeric words in $.*/ say ' rows=' rows /*show number of screen rows.*/ say ' cols=' cols /* " " " " cols.*/
rcd= SysDropFuncs() /*make functions inaccessible*/ if rcd\==0 then do /*examine the return code.*/
say 'return code' rcd "from sysDropFuncs" /*tell about bad " " */
exit rcd /*exit this program with RC. */
end
exit 0 /*stick a fork in it, we're all done. */</lang>
- output (which happens to reflect the program's author's particular screen size for the "DOS" window):
rows= 62
cols= 96
Ruby
This script uses Fiddle from Ruby's standard library to open fakeimglib.so from the C example.
<lang ruby>require 'fiddle/import'
module FakeImgLib
extend Fiddle::Importer
begin
dlload './fakeimglib.so'
extern 'int openimage(const char *)'
rescue Fiddle::DLError
# Either fakeimglib or openimage() is missing.
@@handle = -1
def openimage(path)
$stderr.puts "internal openimage opens #{path}\n"
@@handle += 1
end
module_function :openimage
end
end
handle = FakeImgLib.openimage("path/to/image") puts "opened with handle #{handle}"</lang>
The next script tries to use ImageMagick. First, it tries rmagick from RubyGems. If that library is missing, it tries to use ffi from RubyGems to call C functions in ImageMagick. (FFI is an alternative to Fiddle). If that doesn't work, it falls back to code that only handles PNG images.
<lang ruby># This script shows the width x height of some images.
- Example:
- $ ruby imsize.rb dwarf-vs-elf.png swedish-chef.jpg
- dwarf-vs-elf.png: 242x176
- swedish-chef.jpg: 256x256
begin
require 'rmagick' lib = :rmagick
rescue LoadError
# Missing rmagick. Try ffi.
begin
require 'ffi'
module F
extend FFI::Library
ffi_lib 'MagickWand-6.Q16'
attach_function :DestroyMagickWand, [:pointer], :pointer
attach_function :MagickGetImageHeight, [:pointer], :size_t
attach_function :MagickGetImageWidth, [:pointer], :size_t
attach_function :MagickPingImage, [:pointer, :string], :bool
attach_function :MagickWandGenesis, [], :void
attach_function :NewMagickWand, [], :pointer
end
lib = :ffi
rescue LoadError
# Missing ffi, MagickWand lib, or function in lib.
end
end
case lib when :rmagick
# Returns [width, height] of an image file. def size(path) img = Magick::Image.ping(path).first [img.columns, img.rows] end
when :ffi
F.MagickWandGenesis() def size(path) wand = F.NewMagickWand() F.MagickPingImage(wand, path) or fail 'problem reading image' [F.MagickGetImageWidth(wand), F.MagickGetImageHeight(wand)] ensure F.DestroyMagickWand(wand) if wand end
else
PngSignature = "\x89PNG\r\n\x1A\n".force_encoding('binary')
def size(path)
File.open(path, 'rb') do |file|
# Only works with PNG: https://www.w3.org/TR/PNG/
# Reads [width, height] from IDHR chunk.
# Checks height != nil, but doesn't check CRC of chunk.
sig, width, height = file.read(24).unpack('a8@16NN')
sig == PngSignature and height or fail 'not a PNG image'
[width, height]
end
end
end
- Show the size of each image in ARGV.
status = true ARGV.empty? and (warn "usage: $0 file..."; exit false) ARGV.each do |path|
begin
r, c = size(path)
puts "#{path}: #{r}x#{c}"
rescue
status = false
puts "#{path}: #$!"
end
end exit status</lang>
Rust
The standard library does not provide a way to load dynamic libraries. Without using third-party libraries, we must use the FFI to call the relevant C functions directly.
Unix
<lang rust>#![allow(unused_unsafe)] extern crate libc;
use std::io::{self,Write}; use std::{mem,ffi,process};
use libc::{c_double, RTLD_NOW};
// Small macro which wraps turning a string-literal into a c-string. // This is always safe to call, and the resulting pointer has 'static lifetime macro_rules! to_cstr {
($s:expr) => {unsafe {ffi::CStr::from_bytes_with_nul_unchecked(concat!($s, "\0").as_bytes()).as_ptr()}}
}
macro_rules! from_cstr {
($p:expr) => {ffi::CStr::from_ptr($p).to_string_lossy().as_ref() }
}
fn main() {
unsafe {
let handle = libc::dlopen(to_cstr!("libm.so.6"), RTLD_NOW);
if handle.is_null() {
writeln!(&mut io::stderr(), "{}", from_cstr!(libc::dlerror())).unwrap();
process::exit(1);
}
let extern_cos = libc::dlsym(handle, to_cstr!("cos"))
.as_ref()
.map(mem::transmute::<_,fn (c_double) -> c_double)
.unwrap_or(builtin_cos);
println!("{}", extern_cos(4.0));
}
}
fn builtin_cos(x: c_double) -> c_double {
x.cos()
}</lang>
Scala
Windows
Get free disk space
<lang Scala>import net.java.dev.sna.SNA import com.sun.jna.ptr.IntByReference
object GetDiskFreeSpace extends App with SNA {
snaLibrary = "Kernel32" // Native library name
/*
* Important Note! * * The val holding the SNA-returned function must have the same name as the native function itself * (see line following this comment). This is the only place you specify the native function name. */ val GetDiskFreeSpaceA = SNA[String, IntByReference, IntByReference, IntByReference, IntByReference, Boolean] // This Windows function is described here: // http://msdn.microsoft.com/en-us/library/aa364935(v=vs.85).aspx val (disk, spc, bps, fc, tc) = ("C:\\", new IntByReference, // Sectors per cluster new IntByReference, // Bytes per sector new IntByReference, // Free clusters new IntByReference) // Total clusters
val ok = GetDiskFreeSpaceA(disk, spc, bps, fc, tc) // status
println(f"'$disk%s' ($ok%s): sectors/cluster: ${spc.getValue}%d, bytes/sector: ${bps.getValue}%d, " +
f" free-clusters: ${fc.getValue}%d, total/clusters: ${tc.getValue}%d%n")
}}</lang>
Smalltalk
The code tries to load the fakeimglib (cfr C example); if it succeed, the symbol openimage will exist, and will be called; otherwise, it is executed an "internal" code for openimage. In this example return code of the function of the library is ignored (ValueHolder null) <lang smalltalk>DLD addLibrary: 'fakeimglib'.
Object subclass: ExtLib [
ExtLib class >> openimage: aString [
(CFunctionDescriptor isFunction: 'openimage')
ifTrue: [
(CFunctionDescriptor for: 'openimage'
returning: #int
withArgs: #( #string ) ) callInto: (ValueHolder null).
] ifFalse: [ ('internal open image %1' % { aString }) displayNl ]
]
].
ExtLib openimage: 'test.png'.</lang>
SNOBOL4
This code loads the libm library into the variable ffi_m and binds the hypot() function to the variable ffi_m_hypot. (The variable names are arbitrary.) It then declares a SNOBOL4 function called hypot() which takes two doubles as arguments and returns a double, binding this name to the ffi_m_hypot object returned earlier. It then outputs four hypotenuse calculations using those values. <lang snobol4>-INCLUDE 'ffi.sno'
ffi_m = FFI_DLOPEN('/usr/lib/x86_64-linux-gnu/libm.so')
ffi_m_hypot = FFI_DLSYM(ffi_m, 'hypot')
DEFINE_FFI('hypot(double,double)double', ffi_m_hypot)
OUTPUT = hypot(1,2) OUTPUT = hypot(2,3) OUTPUT = hypot(3,4) OUTPUT = hypot(4,5)
END</lang>
Execution looks like this:
$ snobol4 ffitest.sno 2.23606797749979 3.60555127546399 5. 6.40312423743285
Tcl
<lang Tcl>package require Ffidl
if {[catch {
ffidl::callout OpenImage {pointer-utf8} int [ffidl::symbol fakeimglib.so openimage]
}]} then {
# Create the OpenImage command by other means here...
}
set handle [OpenImage "/the/file/name"]</lang>
Note that if the library is appropriately set up with the correct entry function, it can be accessed directly with load which will cause it to register a Tcl command for the functionality it exports. SWIG can be used to automatically generate the interface code. Alternatively, critcl can be used to allow writing glue C code directly embedded within a Tcl script.
With this many ways to perform the call, the best approach often depends on the size and complexity of the API being mapped. SWIG excels at large APIs, Ffidl is better when you just want to call a particular simple function, and critcl handles complex cases (callbacks, etc.) better than the other two.
TXR
Call uname on Linux
This is the TXR Lisp interactive listener of TXR 176.
Use the :quit command or type Ctrl-D on empty line to exit.
1> (typedef utsarray (zarray 65 char))
#<ffi-type (zarray 65 char)>
2> (typedef utsname (struct utsname (sysname utsarray)
(nodename utsarray)
(release utsarray)
(version utsarray)
(machine utsarray)
(domainname utsarray)))
#<ffi-type (struct utsname (sysname utsarray) (nodename utsarray) (release utsarray)
(version utsarray) (machine utsarray) (domainname utsarray))>
3> (with-dyn-lib nil (deffi uname "uname" int ((ptr-out utsname))))
** warning: (expr-3:1) defun: redefining uname, which is a built-in defun
#:lib-0176
4> (let ((u (new utsname))) (prinl (uname u)) u)
0
#S(utsname sysname "Linux" nodename "zelenka" release "3.2.0-40-generic"
version "#64-Ubuntu SMP Mon Mar 25 21:22:26 UTC 2013" machine "i686"
domainname "(none)")
We use typedef to condense the declarations, much like in C. The FFI handles nested types like arrays in structures.
The zarray type denotes null-terminated arrays. A zarray of char is specialized; it converts between Lisp strings (which use wide characters made of Unicode code points) and C char strings encoded in UTF-8.
The argument of uname is (ptr-out utsname). The semantics of ptr-out in this situation is that FFI prepares a C version of the Lisp structure, but doesn't perform any conversions from Lisp to initialize it. This not only saves CPU cycles, but allows us to use a blank structure produced by (new utsname) all of whose slots are nil and so wouldn't convert to C character arrays anyway! The function is called, and then conversions out of the structure to the Lisp structure take place, filling its slots with string values.
The nil argument in the with-dyn-lib macro causes the underlying implementation to call dlopen(NULL) to get access to the dynamic symbols available in the executable. We can use the name of a shared library instead, or a handle from TXR's dlopen library function.
Ursala
When abs(x) is evaluated, a run time check is performed for the availability of the system library's absolute value function (fabs), and if found, it is used. If not, the user defined replacement function is invoked. <lang Ursala>#import std
- import flo
my_replacement = fleq/0.?/~& negative
abs = math.|fabs my_replacement</lang>
VBA
Here is an example using a Fortran function compiled as a DLL, using Intel Fortran.
First the DLL. Compile with ifort /dll vbafun.f90. The DLL must be in a directory in the PATH environment variable. Notice that for 32 bits VBA, DLL functions must be STDCALL, and not CDECL (the default with Intel Fortran). In 64 bits, there is only one calling convention, so it's not a problem anymore.
<lang fortran>function ffun(x, y)
implicit none !DEC$ ATTRIBUTES DLLEXPORT, STDCALL, REFERENCE :: ffun double precision :: x, y, ffun ffun = x + y * y
end function</lang>
Here is a VBA subroutine using the DLL
<lang vb>Option Explicit Declare Function ffun Lib "vbafun" (ByRef x As Double, ByRef y As Double) As Double Sub Test()
Dim x As Double, y As Double x = 2# y = 10# Debug.Print ffun(x, y)
End Sub</lang>
Wren
An embedded program so we can ask the C host to call the shared library function for us. <lang ecmascript>/* call_shared_library_function.wren */
var RTLD_LAZY = 1
foreign class DL {
construct open(file, mode) {}
foreign call(symbol, arg)
foreign close()
}
class My {
static openimage(s) {
System.print("internal openimage opens %(s)...")
if (!__handle) __handle = 0
__handle = __handle + 1
return __handle - 1
}
}
var file = "fake.img"
var imglib = DL.open("./fakeimglib.so", RTLD_LAZY)
var imghandle = (imglib != null) ? imglib.call("openimage", file) : My.openimage(file)
System.print("opened with handle %(imghandle)")
if (imglib != null) imglib.close()</lang>
We also need to create the shared library, fakeimglib.so, and place it in the current directory.
<lang c>/*
gcc -c -fpic fakeimglib.c gcc -shared fakeimglib.o -o fakeimglib.so
- /
- include <stdio.h>
int openimage(const char *s) {
static int handle = 100; fprintf(stderr, "opening %s\n", s); return handle++;
}</lang>
Finally, we embed the Wren script in the following C program, compile and run it:
<lang c>/* gcc call_shared_library_function.c -o call_shared_library_function -ldl -lwren -lm */
- include <stdio.h>
- include <stdlib.h>
- include <string.h>
- include <dlfcn.h>
- include "wren.h"
/* C <=> Wren interface functions */
void C_dlAllocate(WrenVM* vm) {
const char *file = wrenGetSlotString(vm, 1); int mode = (int)wrenGetSlotDouble(vm, 2); void *imglib = dlopen(file, mode); if (imglib == NULL) wrenSetSlotNull(vm, 0); void** pimglib = (void**)wrenSetSlotNewForeign(vm, 0, 0, sizeof(void*)); *pimglib = imglib;
}
void C_call(WrenVM* vm) {
void *imglib = *(void**)wrenGetSlotForeign(vm, 0); const char *symbol = wrenGetSlotString(vm, 1); const char *arg = wrenGetSlotString(vm, 2); int (*extopenimage)(const char *); extopenimage = dlsym(imglib, symbol); int imghandle = extopenimage(arg); wrenSetSlotDouble(vm, 0, (double)imghandle);
}
void C_close(WrenVM* vm) {
void *imglib = *(void**)wrenGetSlotForeign(vm, 0); dlclose(imglib);
}
WrenForeignClassMethods bindForeignClass(WrenVM* vm, const char* module, const char* className) {
WrenForeignClassMethods methods;
methods.finalize = NULL;
if (strcmp(module, "main") == 0) {
if (strcmp(className, "DL") == 0) {
methods.allocate = C_dlAllocate;
}
}
return methods;
}
WrenForeignMethodFn bindForeignMethod(
WrenVM* vm,
const char* module,
const char* className,
bool isStatic,
const char* signature) {
if (strcmp(module, "main") == 0) {
if (strcmp(className, "DL") == 0) {
if (!isStatic && strcmp(signature, "call(_,_)") == 0) return C_call;
if (!isStatic && strcmp(signature, "close()") == 0) return C_close;
}
}
return NULL;
}
static void writeFn(WrenVM* vm, const char* text) {
printf("%s", text);
}
void errorFn(WrenVM* vm, WrenErrorType errorType, const char* module, const int line, const char* msg) {
switch (errorType) {
case WREN_ERROR_COMPILE:
printf("[%s line %d] [Error] %s\n", module, line, msg);
break;
case WREN_ERROR_STACK_TRACE:
printf("[%s line %d] in %s\n", module, line, msg);
break;
case WREN_ERROR_RUNTIME:
printf("[Runtime Error] %s\n", msg);
break;
}
}
char *readFile(const char *fileName) {
FILE *f = fopen(fileName, "r"); fseek(f, 0, SEEK_END); long fsize = ftell(f); rewind(f); char *script = malloc(fsize + 1); fread(script, 1, fsize, f); fclose(f); script[fsize] = 0; return script;
}
int main(int argc, char **argv) {
WrenConfiguration config;
wrenInitConfiguration(&config);
config.writeFn = &writeFn;
config.errorFn = &errorFn;
config.bindForeignClassFn = &bindForeignClass;
config.bindForeignMethodFn = &bindForeignMethod;
WrenVM* vm = wrenNewVM(&config);
const char* module = "main";
const char* fileName = "call_shared_library_function.wren";
char *script = readFile(fileName);
WrenInterpretResult result = wrenInterpret(vm, module, script);
switch (result) {
case WREN_RESULT_COMPILE_ERROR:
printf("Compile Error!\n");
break;
case WREN_RESULT_RUNTIME_ERROR:
printf("Runtime Error!\n");
break;
case WREN_RESULT_SUCCESS:
break;
}
wrenFreeVM(vm);
free(script);
return 0;
}</lang>
- Output:
Same as C example depending on whether fakeimglib.so is present in the current directory or not.
X86-64 Assembly
UASM 2.52
<lang asm> option casemap:none
windows64 equ 1 linux64 equ 3
ifndef __LIB_CLASS__ __LIB_CLASS__ equ 1
if @Platform eq windows64
option dllimport:<kernel32>
HeapAlloc proto :qword, :dword, :qword
HeapFree proto :qword, :dword, :qword
ExitProcess proto :dword
GetProcessHeap proto
LoadLibraryA proto :qword
FreeLibrary proto :qword
GetProcAddress proto :qword, :qword
option dllimport:none
exit equ ExitProcess
dlsym equ GetProcAddress
dlclose equ FreeLibrary
elseif @Platform eq linux64
malloc proto :qword
free proto :qword
exit proto :dword
dlclose proto :qword
dlopen proto :qword, :dword
dlsym proto :qword, :qword
endif
printf proto :qword, :vararg
CLASS libldr CMETHOD getproc ENDMETHODS libname db 100 dup (0) plib dq ? ENDCLASS
METHOD libldr, Init, <VOIDARG>, <>, library:qword, namelen:qword
mov rbx, thisPtr
assume rbx:ptr libldr
.if library != 0
mov rcx, namelen
mov rsi, library
lea rdi, [rbx].libname
rep movsb
if @Platform eq windows64
invoke LoadLibraryA, addr [rbx].libname
.if rax == 0
invoke printf, CSTR("--> Failed to load library",10)
.else
mov [rbx].plib, rax
.endif
elseif @Platform eq linux64
invoke dlopen, addr [rbx].libname, 1
.if rax == 0
lea rax, [rbx].libname
invoke printf, CSTR("--> Failed to load library %s",10), rax
.else
mov [rbx].plib, rax
.endif
endif
.else
invoke printf, CSTR("--> Library name to load required..",10)
.endif
mov rax, rbx
assume rbx:nothing
ret
ENDMETHOD
METHOD libldr, getproc, <VOIDARG>, <>, func:qword local tmp:qword mov tmp, func ;; Just return RAX.. invoke dlsym, [thisPtr].libldr.plib, tmp ret ENDMETHOD
METHOD libldr, Destroy, <VOIDARG>, <>
mov rbx, thisPtr
assume rbx:ptr libldr
.if [rbx].plib != 0
invoke dlclose, [rbx].plib
.endif
assume rbx:nothing
ret
ENDMETHOD
endif
.data LibName db "./somelib.l",0
.code main proc
local ldr:ptr libldr
invoke printf, CSTR("--> Loading %s .. ",10), addr LibName
mov ldr, _NEW(libldr, addr LibName, sizeof(LibName))
ldr->getproc(CSTR("disappointment"))
.if rax == 0
lea rax, idisappointment
.endif
call rax
_DELETE(ldr)
invoke exit, 0
ret
main endp
idisappointment:
push rbp
mov rbp, rsp
invoke printf, CSTR("--> Well this is a internal disappointment..",10)
pop rbp
mov rax, 0
ret
end </lang> It's worth pointing out that under linux, dlopen CAN return NULL WITHOUT it being an error. One SHOULD call dlerror() to check for actual errors.
- Output:
--> Loading ./somelib.l .. --> Well this is a external disappointment.. And on failure... --> Loading ./somelib.l .. --> Failed to load library ./somelib.l --> Well this is a internal disappointment..
zkl
In zkl, extensions/new objects are written in C as shared libraries. For example, big nums are implemented as a small glue library in front of GMP: <lang zkl>var BN=Import("zklBigNum"); BN(1)+2 //--> BN(3)</lang> and it "just works" as all objects are "the same" whether statically or dynamically linked.
- Programming Tasks
- Programming environment operations
- Ada
- Arturo
- AutoHotkey
- BaCon
- BBC BASIC
- C
- C sharp
- COBOL
- Common Lisp
- CFFI
- Crystal
- D
- Dart
- Delphi
- Forth
- Fortran
- FreeBASIC
- Go
- Haskell
- Unix
- J
- Java
- JNA
- Jsish
- Julia
- Kotlin
- Lingo
- Lua
- Maple
- Mathematica
- Wolfram Language
- Nim
- OCaml
- Ol
- OxygenBasic
- PARI/GP
- Pascal
- Perl
- Phix
- PicoLisp
- PowerBASIC
- PureBasic
- Python
- QB64
- R
- Racket
- Raku
- REXX
- Ruby
- ImageMagick
- RubyGems
- Rust
- Scala
- Net.java.dev.sna.SNA
- Smalltalk
- SNOBOL4
- Tcl
- Ffidl
- TXR
- Ursala
- VBA
- Wren
- X86-64 Assembly
- Zkl
- Batch File/Omit
- GUISS/Omit
- M4/Omit
- Maxima/Omit
- ML/I/Omit
- TI-83 BASIC/Omit
- TI-89 BASIC/Omit
- Scheme/Omit
- Retro/Omit
- Functions and subroutines