Stack traces
You are encouraged to solve this task according to the task description, using any language you may know.
Many programming languages allow for introspection of the current call stack environment. This can be for a variety of purposes such as enforcing security checks, debugging, or for getting access to the stack frame of callers.
This task calls for you to print out (in a manner considered suitable for the platform) the current call stack. The amount of information printed for each frame on the call stack is not constrained, but should include at least the name of the function or method at that level of the stack frame. You may explicitly add a call to produce the stack trace to the (example) code being instrumented for examination.
The task should allow the program to continue after generating the stack trace. The task report here must include the trace from a sample program.
Ada
The provided solution is specific to the GNAT Ada compiler. Further it is restricted to some platforms. See the description of the package GNAT.Traceback supplied with GNAT. The switch -g must be used in order to include debug information into the executable. <lang Ada>with Ada.Text_IO; use Ada.Text_IO; with GNAT.Traceback; with GNAT.Traceback.Symbolic;
procedure Test_Stack_Trace is
procedure Call_Stack is
Trace : GNAT.Traceback.Tracebacks_Array (1..1_000);
Length : Natural;
begin
GNAT.Traceback.Call_Chain (Trace, Length);
Put_Line (GNAT.Traceback.Symbolic.Symbolic_Traceback (Trace (1..Length)));
end Call_Stack;
procedure Inner (K : Integer) is
begin
Call_Stack;
end Inner;
procedure Middle (X, Y : Integer) is
begin
Inner (X * Y);
end Middle;
procedure Outer (A, B, C : Integer) is
begin
Middle (A + B, B + C);
end Outer;
begin
Outer (2,3,5);
end Test_Stack_Trace;</lang> Sample output:
00417D7F in ?? at cygming-crtend.c:0 00401A61 in test_stack_trace.call_stack at test_stack_trace.adb:10 00401A25 in test_stack_trace.inner at test_stack_trace.adb:16 00401A0C in test_stack_trace.middle at test_stack_trace.adb:21 0040193E in test_stack_trace.outer at test_stack_trace.adb:26 004018A2 in _ada_test_stack_trace at test_stack_trace.adb:30 004016BE in main at b~test_stack_trace.adb:183 00401235 in ?? at cygming-crtend.c:0 00401286 in ?? at cygming-crtend.c:0 7C817075 in ?? at ??:0
AutoHotkey
The local, static, and global bindings are viewable using 'Listvars'
recently executed lines are available through ListLines
ListLines can be turned on or off... with:
ListLines, On|Off
<lang autohotkey>f()
return
f() { return g() }
g() { ListLines msgbox, lines recently executed x = local to g ListVars msgbox, variable bindings }
- Persistent</lang>
Output: <lang autohotkey>001: f() 006: Return,g() 011: ListLines (0.05) 012: MsgBox,lines recently executed (3.81) 013: x = local to g 014: ListVars 015: MsgBox,variable bindings (3.94) 016: } 002: Return (181.66)
Global Variables (alphabetical)
0[1 of 3]: 0 ErrorLevel[1 of 3]: 0 </lang>
BASIC
On Beta BASIC and SAM BASIC, the call stack is used for procedure calls, GOSUBs and DO loops. The stack contains return addresses as line and statement numbers. (The parameters for procedures are stored in another stack.) POP statement can be used to pop the return address from the stack.
The following procedure pops the return addrsses from the stack and lists the corresponding lines where the call occurred. Since it is not possible to push the addresses back into the stack, it is not possible to continue the normal flow of execution after displaying the stack. However, it is possible to continue the program otherwise. If the program execution stops on error, it is possible to display the call stack by typing callstack in command mode.
100 DEF PROC callstack 110 ON ERROR GOTO 1000 120 FOR i=1 TO 100 130 POP lnum 140 LIST lnum TO lnum 150 NEXT i 190 END PROC 1000 PRINT "End of stack" 1010 STOP
Example usage. An error is generated on line 320, which causes branch to error handler on line 1100. The error handler displays error number followed by call stack.
200 DEF PROC foo count 210 PRINT "foo "; 220 IF count > 1 230 foo count-1 240 ELSE 250 bar 260 END IF 290 END PROC 300 DEF PROC bar 310 PRINT "bar" 320 x = 1/0 390 END PROC 500 ON ERROR GOTO 1100 510 foo 3 520 STOP 1100 PRINT "Error "; error; " on line "; lino 1110 PRINT "Callstack:" 1120 callstack 1130 STOP
Output:
foo foo foo bar Error 28 on line 320 Call stack: 1120 callstack 320 x = 1/0 250 bar 230 foo count-1 230 foo count-1 510 foo 3 End of stack
C
Using GNU extensions
The backtrace* functions are a GNU extension to the standard C library.
In order to be able to see the symbols, we need to link with an option telling to export symbols names in the dynamic section (for ELF and targets supporting it); for gcc, it means using the option -rdynamic (or -export-dynamic in the GNU linker). Otherwise we see only addresses. Static functions will always have their names "hidden".
<lang c>#include <stdio.h>
- include <stdlib.h>
- include <unistd.h>
- include <execinfo.h>
- define MAX_BT 200
void print_stack_trace() {
void *buffer[MAX_BT]; int n;
n = backtrace(buffer, MAX_BT); fprintf(stderr, "--- (depth %d) ---\n", n); backtrace_symbols_fd(buffer, n, STDERR_FILENO);
}
void inner(int k)
{
print_stack_trace();
}
void middle(int x, int y) {
inner(x*y);
}
void outer(int a, int b, int c) {
middle(a+b, b+c);
}
int main() {
outer(2,3,5); return EXIT_SUCCESS;
}</lang>
Sample output on my system:
--- (depth 7) --- ./pst(print_stack_trace+0x1f)[0x8048683] ./pst(inner+0xb)[0x80486cd] ./pst(middle+0x15)[0x80486e4] ./pst(outer+0x23)[0x8048709] ./pst(main+0x2d)[0x8048738] /lib/i686/libc.so.6(__libc_start_main+0xe5)[0xb7e045c5] ./pst[0x80485d1]
Using no extensions
Sometimes microcomputers do not come with any kind of debug or stack tracing routines. Typically a program would "just hang" somewhere, or crash the gadget. This then requires manually "wolf fencing" of the bug with printf statements to identify the C source file, then the procedure, and then the line at the point of system crash.
The following macros and procedures provide an alternative way of doing this trouble shooting.
The steps are:
- #include "stack_trace.h" in the suspect C source code.
- Change the initial and last { and } of each procedure in the code to BEGIN(proc_name) and END.
- #define STACK_TRACE_ON and assign stack_trace.on to TRUE
- Recompile and run....
The resulting output can be used to locate offending procedure and - hopefully - give a hint to the location of the actual bug.
The key point is that the following can be done on systems that are equipped with only and editor and compiler, and no debugger or library extension.
==> stack_trace.h <== <lang C> /* stack_trace.c - macros for hinting/tracing where a program crashed
on a system _without_ any form of debugger.
Simple goodbye_cruel_world.c example:
- include <stdio.h>
- include <stdlib.h>
- define STACK_TRACE_ON // compile in these "stack_trace" routines
- include "stack_trace.h"
void goodbye_cruel_world() BEGIN(goodbye_cruel_world)
print_stack_trace();
for(;;){}
END
int main() BEGIN(main)
stack_trace.on = TRUE; // turn on runtime tracing goodbye_cruel_world(); stack_trace.on = FALSE; RETURN(EXIT_SUCCESS);
END
Output: goodbye_cruel_world.c:8: BEGIN goodbye_cruel_world[0x80486a8], stack(depth:1, size:60) goodbye_cruel_world.c:8: goodbye_cruel_world[0x80486a8] --- stack(depth:2, size:60) --- goodbye_cruel_world.c:14: main[0x80486f4] --- stack(depth:1, size:0) --- goodbye_cruel_world.c:8: --- (depth 2) ---
- /
- ifndef _LINUX_STDDEF_H
- include <stddef.h>
- endif
typedef struct stack_trace_frame_s {
const char *file_name; int file_line; const char *proc_name; void *proc_addr; struct stack_trace_frame_s *down, *up;
} stack_trace_frame_t;
- define SKIP
typedef enum {TRUE=1, FALSE=0} bool_t;
typedef struct {
bool_t on;
struct { const char *_begin, *_print, *_return, *_exit, *_end; } fmt;
struct { int depth; stack_trace_frame_t *lwb, *upb; } stack;
struct { int lwb, by, upb; const char *prefix; } indent;
} stack_trace_t;
extern stack_trace_t stack_trace;
void stack_trace_begin(char *SKIP, stack_trace_frame_t *SKIP); void stack_trace_end(char *SKIP, int SKIP); void print_stack_trace();
- ifdef STACK_TRACE_ON
/* Many ThanX to Steve R Bourne for inspiring the following macros ;-) */
- define BEGIN(x) { auto stack_trace_frame_t this = {__FILE__, __LINE__, #x, &x, NULL, NULL}; \
stack_trace_begin(stack_trace.fmt._begin, &this); {
- define RETURN(x) { stack_trace_end(stack_trace.fmt._return, __LINE__); return(x); }
- define EXIT(x) { stack_trace_end(stack_trace.fmt._exit, __LINE__); exit(x); }
- define END } stack_trace_end(stack_trace.fmt._end, __LINE__); }
- else
/* Apologies to Landon Curt Noll and Larry Bassel for the following macros :-) */
- define BEGIN(x) {
- define RETURN(x) return(x)
- define EXIT(x) exit(x)
- define END }
- endif</lang>
==> stack_trace.c <== <lang C>#include <stdio.h>
- include <stddef.h>
- define STACK_TRACE_ON
- include "stack_trace.h"
- define indent_fmt "%s"
- define std_cc_diag_fmt "%s:%d: "
- define stack_trace_diag_fmt " %s[0x%x], stack(depth:%d, size:%u)\n"
- define stack_trace_fmt "%s:%d:\t%s[0x%x]\t--- stack(depth:%d, size:%u) ---\n"
stack_trace_t stack_trace = {
FALSE, /* default: stack_trace.on == FALSE */
{ std_cc_diag_fmt""indent_fmt"BEGIN"stack_trace_diag_fmt,
stack_trace_fmt,
std_cc_diag_fmt""indent_fmt"RETURN"stack_trace_diag_fmt,
std_cc_diag_fmt""indent_fmt"EXIT"stack_trace_diag_fmt,
std_cc_diag_fmt""indent_fmt"END"stack_trace_diag_fmt },
{ 0, (stack_trace_frame_t*)NULL, (stack_trace_frame_t*)NULL }, /* stack */
{ 19, 2, 20, " " } /* indent wrap */
};
void stack_trace_begin(const char *fmt, stack_trace_frame_t *this){
if(stack_trace.on){
fprintf(stderr, fmt,
this->file_name, this->file_line, /* file details */
stack_trace.indent.prefix+stack_trace.indent.lwb,
this->proc_name, this->proc_addr, /* procedure details */
stack_trace.stack.depth, (unsigned)stack_trace.stack.lwb-(unsigned)this);
stack_trace.indent.lwb =
( stack_trace.indent.lwb - stack_trace.indent.by ) % stack_trace.indent.upb;
}
if(!stack_trace.stack.upb){ /* this IS the stack !! */
stack_trace.stack.lwb = stack_trace.stack.upb = this;
} else {
this -> down = stack_trace.stack.upb;
stack_trace.stack.upb -> up = this;
stack_trace.stack.upb = this;
}
stack_trace.stack.depth++;
}
void stack_trace_end(const char *fmt, int line){
stack_trace.stack.depth--;
if(stack_trace.on){
stack_trace.indent.lwb =
( stack_trace.indent.lwb + stack_trace.indent.by ) % stack_trace.indent.upb;
stack_trace_frame_t *this = stack_trace.stack.upb;
fprintf(stderr, fmt,
this->file_name, this->file_line, /* file details */
stack_trace.indent.prefix+stack_trace.indent.lwb,
this->proc_name, this->proc_addr, /* procedure details */
stack_trace.stack.depth, (unsigned)stack_trace.stack.lwb-(unsigned)this);
}
stack_trace.stack.upb = stack_trace.stack.upb -> down;
}
void print_indent(){
if(!stack_trace.stack.upb){
/* fprintf(stderr, "STACK_TRACE_ON not #defined during compilation\n"); */
} else {
stack_trace_frame_t *this = stack_trace.stack.upb;
fprintf(stderr, std_cc_diag_fmt""indent_fmt,
this->file_name, this->file_line, /* file details */
stack_trace.indent.prefix+stack_trace.indent.lwb
);
}
}
void print_stack_trace() {
if(!stack_trace.stack.upb){
/* fprintf(stderr, "STACK_TRACE_ON not #defined during compilation\n"); */
} else {
int depth = stack_trace.stack.depth;
stack_trace_frame_t *this = stack_trace.stack.upb;
for(this = stack_trace.stack.upb; this; this = this->down, depth--){
fprintf(stderr, stack_trace.fmt._print,
this->file_name, this->file_line, /* file details */
this->proc_name, this->proc_addr, /* procedure details */
depth, (unsigned)stack_trace.stack.lwb-(unsigned)this);
}
print_indent(); fprintf(stderr, "--- (depth %d) ---\n", stack_trace.stack.depth);
}
}</lang>
==> stack_trace_test.c <==
The following code demonstrates the usage of the macros. Note that the initial and last curly brackets have been changed to BEGIN(procedure_name) and END. This is sometimes called macro magic and is unfashionable.
<lang C>#include <stdio.h>
- include <stdlib.h>
- define STACK_TRACE_ON /* compile in these "stack_trace" routines */
- include "stack_trace.h"
void inner(int k) BEGIN(inner)
print_indent(); printf("*** Now dump the stack ***\n");
print_stack_trace();
END
void middle(int x, int y) BEGIN(middle)
inner(x*y);
END
void outer(int a, int b, int c) BEGIN(outer)
middle(a+b, b+c);
END
int main() BEGIN(main)
stack_trace.on = TRUE; /* turn on runtime tracing */ outer(2,3,5); stack_trace.on = FALSE; RETURN(EXIT_SUCCESS);
END</lang>
- Output:
stack_trace_test.c:19: BEGIN outer[0x80487b4], stack(depth:1, size:60) stack_trace_test.c:14: BEGIN middle[0x8048749], stack(depth:2, size:108) stack_trace_test.c:8: BEGIN inner[0x80486d8], stack(depth:3, size:156) stack_trace_test.c:8: *** Now dump the stack *** stack_trace_test.c:8: inner[0x80486d8] --- stack(depth:4, size:156) --- stack_trace_test.c:14: middle[0x8048749] --- stack(depth:3, size:108) --- stack_trace_test.c:19: outer[0x80487b4] --- stack(depth:2, size:60) --- stack_trace_test.c:24: main[0x804882a] --- stack(depth:1, size:0) --- stack_trace_test.c:8: --- (depth 4) --- stack_trace_test.c:8: END inner[0x80486d8], stack(depth:3, size:156) stack_trace_test.c:14: END middle[0x8048749], stack(depth:2, size:108) stack_trace_test.c:19: END outer[0x80487b4], stack(depth:1, size:60)
C#
<lang csharp>using System; using System.Diagnostics;
class Program {
static void Inner()
{
Console.WriteLine(new StackTrace());
}
static void Middle()
{
Inner();
}
static void Outer()
{
Middle();
}
static void Main()
{
Outer();
}
}</lang> Sample output: <lang>at Program.Inner() at Program.Middle() at Program.Outer() at Program.Main()</lang>
Clojure
ThreadMXBean can be used to show you the stack of all live threads.
<lang clojure> (doall
(map println (.dumpAllThreads (java.lang.management.ManagementFactory/getThreadMXBean) false false)))
</lang>
- Output:
#<ThreadInfo "nREPL-worker-26" Id=64 RUNNABLE
at sun.management.ThreadImpl.dumpThreads0(Native Method)
at sun.management.ThreadImpl.dumpAllThreads(ThreadImpl.java:446)
at user$eval1285.invoke(form-init6675235431801252432.clj:1)
at clojure.lang.Compiler.eval(Compiler.java:6619)
at clojure.lang.Compiler.eval(Compiler.java:6582)
at clojure.core$eval.invoke(core.clj:2852)
at clojure.main$repl$read_eval_print__6588$fn__6591.invoke(main.clj:259)
at clojure.main$repl$read_eval_print__6588.invoke(main.clj:259)
...
Common Lisp
Stack trace facilities are not specified by the Common Lisp standard. Implementations vary widely in the amount of information provided, how it can be retrieved, and the amount of internal implementation detail included.
Here we use SWANK, which a component of SLIME, a Common Lisp IDE (it is the library loaded into the target Lisp system to enable interaction and remote debugging), to make use of its portable debugging facilities:
<lang lisp>(swank-backend:call-with-debugging-environment
(lambda () (swank:backtrace 0 nil)))</lang>
Here are a few lines of the result when running under SBCL, the rest is omitted since it's long and boring: <lang lisp>((0 "((LAMBDA (SWANK-BACKEND::DEBUGGER-LOOP-FN)) #<FUNCTION (LAMBDA #) {100459BBC9}>)")
(1 "(SB-INT:SIMPLE-EVAL-IN-LEXENV (SWANK-BACKEND:CALL-WITH-DEBUGGING-ENVIRONMENT (LAMBDA () (SWANK:BACKTRACE 0 NIL))) #<NULL-LEXENV>)") (2 "(SWANK::EVAL-REGION \"(swank-backend:call-with-debugging-environment\\n (lambda ()\\n (swank:backtrace 0 nil)))\\n\\n\")") (3 "((LAMBDA ()))") ...)</lang>
Note that this is a data structure containing the backtrace, not a format intended for presentation. In SBCL, executing (sb-debug:backtrace 7) produces output like this (run from the SLIME-REPL, which is why it still contains mentions of SWANK):
<lang lisp>CL-USER> (sb-debug:backtrace 7) 0: (SB-DEBUG::MAP-BACKTRACE
#<CLOSURE (LAMBDA (SB-DEBUG::FRAME)) {1193EFCD}>)[:EXTERNAL]
1: (BACKTRACE
7
#<TWO-WAY-STREAM
:INPUT-STREAM #<SWANK-BACKEND::SLIME-INPUT-STREAM {120F6519}>
:OUTPUT-STREAM #<SWANK-BACKEND::SLIME-OUTPUT-STREAM {1208F3E1}>>)
2: (SB-INT:SIMPLE-EVAL-IN-LEXENV (BACKTRACE 7) #<NULL-LEXENV>) 3: (SWANK::EVAL-REGION
"(sb-debug:backtrace 7)
") 4: ((LAMBDA ())) 5: (SWANK::TRACK-PACKAGE #<CLOSURE (LAMBDA ()) {1193ECBD}>) 6: (SWANK::CALL-WITH-RETRY-RESTART
"Retry SLIME REPL evaluation request."
#<CLOSURE (LAMBDA ()) {1193EC4D}>)</lang>
SBCL's backtraces consist entirely of lists of the form (function-name args...).
D
Compiled with the dmd compiler using the -g switch.
<lang d>import std.stdio, core.runtime;
void inner() { defaultTraceHandler.writeln; } void middle() { inner; } void outer() { middle; }
void main() {
outer; "After the stack trace.".writeln;
}</lang>
- Output:
0x00404FBE in core.sys.windows.stacktrace.StackTrace core.sys.windows.stacktrace.StackTrace.__ctor(uint, core.sys.windows.windows.CONTEXT*) at E:\dmd2\src\druntime\import\core\sys\windows\stacktrace.d(69) 0x00404ACB in object.Throwable.TraceInfo core.runtime.defaultTraceHandler(void*) at E:\dmd2\src\druntime\import\core\runtime.d(646) 0x0040201A in void test.inner() at E:\test.d(3) 0x0040202C in void test.middle() at E:\test.d(4) 0x00402038 in void test.outer() at E:\test.d(5) 0x00402044 in _Dmain at E:\test.d(9) 0x00409AAC in void rt.dmain2._d_run_main(int, char**, extern (C) int function(char[][])*).runAll().void __lambda1() 0x00409A7F in void rt.dmain2._d_run_main(int, char**, extern (C) int function(char[][])*).runAll() 0x00409997 in _d_run_main 0x004048D8 in main 0x0041FB2D in mainCRTStartup 0x76EED2E9 in BaseThreadInitThunk 0x77821603 in RtlInitializeExceptionChain 0x778215D6 in RtlInitializeExceptionChain After the stack trace.
DWScript
Stack traces can be obtained from exception objects <lang delphi>procedure Inner; begin
try
raise Exception.Create();
except
on E: Exception do
PrintLn(E.StackTrace);
end;
end;
procedure Middle; begin
Inner;
end;
procedure Outer; begin
Middle;
end;
Outer;</lang>
Output:
Inner [line: 4, column: 23] Middle [line: 13, column: 4] Outer [line: 18, column: 4] [line: 21, column: 1]
Elixir
<lang elixir>defmodule Stack_traces do
def main do
{:ok, a} = outer
IO.inspect a
end
defp outer do
{:ok, a} = middle
{:ok, a}
end
defp middle do
{:ok, a} = inner
{:ok, a}
end
defp inner do
try do
throw(42)
catch 42 -> {:ok, :erlang.get_stacktrace}
end
end
end
Stack_traces.main</lang>
- Output:
[{Stack_traces, :inner, 0, [file: 'stack_trace.exs', line: 19]},
{Stack_traces, :middle, 0, [file: 'stack_trace.exs', line: 13]},
{Stack_traces, :outer, 0, [file: 'stack_trace.exs', line: 8]},
{Stack_traces, :main, 0, [file: 'stack_trace.exs', line: 3]},
{:elixir_compiler, :dispatch_loaded, 6,
[file: 'src/elixir_compiler.erl', line: 125]},
{:elixir_lexical, :run, 3, [file: 'src/elixir_lexical.erl', line: 16]},
{:elixir_compiler, :quoted, 3, [file: 'src/elixir_compiler.erl', line: 30]},
{Code, :require_file, 2, [file: 'lib/code.ex', line: 363]}]
Erlang
Stack traces only can be obtained inside a catch block. Additionally, it doesn't work for tail calls. <lang erlang>-module(stack_traces).
-export([main/0]).
main() -> {ok,A} = outer(), io:format("~p\n", [A]).
outer() -> {ok,A} = middle(), {ok,A}.
middle() -> {ok,A} = inner(), {ok,A}.
inner() -> try throw(42) catch 42 -> {ok,erlang:get_stacktrace()} end.</lang>
- Output:
[{stack_traces,inner,0,[{file,"stack_traces.erl"},{line,18}]},
{stack_traces,middle,0,[{file,"stack_traces.erl"},{line,14}]},
{stack_traces,outer,0,[{file,"stack_traces.erl"},{line,10}]},
{stack_traces,main,0,[{file,"stack_traces.erl"},{line,6}]},
{init,start_it,1,[]},
{init,start_em,1,[]}]
F#
<lang fsharp>open System.Diagnostics
type myClass() =
member this.inner() = printfn "%A" (new StackTrace()) member this.middle() = this.inner() member this.outer() = this.middle()
[<EntryPoint>] let main args =
let that = new myClass() that.outer() 0</lang>
Output
at Rosetta.myClass.inner() at Rosetta.myClass.middle() at Rosetta.myClass.outer() at Rosetta.main(String[] args)
Forth
In Forth, calling sequence information is kept on the Return Stack. Some Forth compilers have the word "R.S" that dumps the contents of the Return Stack - just like ".S", which dumps the contents of the Data Stack. Note this may also include stack frames, local variables and temporary values. Forth has no way of knowing which is which, because that is usually left to the programmer.
<lang forth>[UNDEFINED] R.S [IF] \ Return stack counterpart of DEPTH \ Note the STACK-CELLS correction is there to hide RDEPTH itself
( -- n)
- RDEPTH STACK-CELLS -2 [+] CELLS RP@ - ;
\ Return stack counterpart of .S \ Note the : R.S R> .. >R ; sequence is there to hide R.S itself
( --)
- R.S R> CR RDEPTH DUP 0> IF DUP
BEGIN DUP WHILE R> -ROT 1- REPEAT DROP DUP BEGIN DUP WHILE ROT DUP . >R 1- REPEAT DROP THEN ." (TORS) " DROP >R ;
[THEN]</lang>
Go
<lang go>package main
import (
"fmt" "runtime"
)
func main() {
stackTrace := make([]byte, 1024)
n := runtime.Stack(stackTrace, true)
stackTrace = stackTrace[:n]
fmt.Printf("%s\n", stackTrace)
fmt.Printf("(%d bytes)\n", len(stackTrace))
}</lang> outputs:
goroutine 16 [running]: main.main() /tmpfs/gosandbox-efa5a722_5cfcad46_bebc14b4_0486dec5_bd9e34fc/prog.go:10 +0xa0 goroutine 19 [runnable]: runfinq() /tmp/sandbox/go/src/pkg/runtime/mgc0.c:2606 runtime.goexit() /tmp/sandbox/go/src/pkg/runtime/proc.c:1445 (259 bytes)
Groovy
Solution: <lang groovy>def rawTrace = { Thread.currentThread().stackTrace }</lang>
Test: (demonstrates, among other things, continued execution after generating stack trace) <lang groovy>def trace = rawTrace().collect {
def props = it.properties
def keys = (it.properties.keySet() - (new Object().properties.keySet()))
props.findAll{ k, v -> k in keys }
}
def propNames = trace[0].keySet().sort() def propWidths = propNames.collect { name -> [name, trace.collect{ it[name].toString() }].flatten()*.size().max() }
propNames.eachWithIndex{ name, i -> printf("%-${propWidths[i]}s ", name) }; println propWidths.each{ width -> print('-' * width + ' ') }; println trace.each {
propNames.eachWithIndex{ name, i -> printf("%-${propWidths[i]}s ", it[name].toString()) }; println
}</lang>
Output:
className fileName lineNumber methodName nativeMethod ----------------------------------------------------------------- --------------------------------- ---------- ------------------------------- ------------ java.lang.Thread Thread.java 1479 getStackTrace false sun.reflect.NativeMethodAccessorImpl NativeMethodAccessorImpl.java -2 invoke0 true sun.reflect.NativeMethodAccessorImpl NativeMethodAccessorImpl.java 39 invoke false sun.reflect.DelegatingMethodAccessorImpl DelegatingMethodAccessorImpl.java 25 invoke false java.lang.reflect.Method Method.java 597 invoke false org.codehaus.groovy.reflection.CachedMethod CachedMethod.java 90 invoke false groovy.lang.MetaMethod MetaMethod.java 233 doMethodInvoke false groovy.lang.MetaClassImpl$GetBeanMethodMetaProperty MetaClassImpl.java 3465 getProperty false org.codehaus.groovy.runtime.callsite.GetEffectivePojoPropertySite GetEffectivePojoPropertySite.java 61 getProperty false org.codehaus.groovy.runtime.callsite.AbstractCallSite AbstractCallSite.java 227 callGetProperty false ConsoleScript38$_run_closure1 ConsoleScript38 1 doCall false sun.reflect.NativeMethodAccessorImpl NativeMethodAccessorImpl.java -2 invoke0 true sun.reflect.NativeMethodAccessorImpl NativeMethodAccessorImpl.java 39 invoke false sun.reflect.DelegatingMethodAccessorImpl DelegatingMethodAccessorImpl.java 25 invoke false java.lang.reflect.Method Method.java 597 invoke false org.codehaus.groovy.reflection.CachedMethod CachedMethod.java 90 invoke false groovy.lang.MetaMethod MetaMethod.java 233 doMethodInvoke false org.codehaus.groovy.runtime.metaclass.ClosureMetaClass ClosureMetaClass.java 272 invokeMethod false groovy.lang.MetaClassImpl MetaClassImpl.java 885 invokeMethod false org.codehaus.groovy.runtime.callsite.PogoMetaClassSite PogoMetaClassSite.java 66 callCurrent false org.codehaus.groovy.runtime.callsite.CallSiteArray CallSiteArray.java 46 defaultCallCurrent false org.codehaus.groovy.runtime.callsite.AbstractCallSite AbstractCallSite.java 133 callCurrent false org.codehaus.groovy.runtime.callsite.AbstractCallSite AbstractCallSite.java 141 callCurrent false ConsoleScript38$_run_closure1 ConsoleScript38 -1 doCall false sun.reflect.NativeMethodAccessorImpl NativeMethodAccessorImpl.java -2 invoke0 true sun.reflect.NativeMethodAccessorImpl NativeMethodAccessorImpl.java 39 invoke false sun.reflect.DelegatingMethodAccessorImpl DelegatingMethodAccessorImpl.java 25 invoke false java.lang.reflect.Method Method.java 597 invoke false org.codehaus.groovy.reflection.CachedMethod CachedMethod.java 90 invoke false groovy.lang.MetaMethod MetaMethod.java 233 doMethodInvoke false org.codehaus.groovy.runtime.metaclass.ClosureMetaClass ClosureMetaClass.java 272 invokeMethod false groovy.lang.MetaClassImpl MetaClassImpl.java 885 invokeMethod false org.codehaus.groovy.runtime.callsite.PogoMetaClassSite PogoMetaClassSite.java 39 call false org.codehaus.groovy.runtime.callsite.CallSiteArray CallSiteArray.java 42 defaultCall false org.codehaus.groovy.runtime.callsite.AbstractCallSite AbstractCallSite.java 108 call false org.codehaus.groovy.runtime.callsite.AbstractCallSite AbstractCallSite.java 112 call false ConsoleScript38 ConsoleScript38 3 run false groovy.lang.GroovyShell GroovyShell.java 266 runScriptOrMainOrTestOrRunnable false groovy.lang.GroovyShell GroovyShell.java 517 run false groovy.lang.GroovyShell GroovyShell.java 172 run false groovy.lang.GroovyShell$run null -1 call false groovy.ui.Console$_runScriptImpl_closure16 Console.groovy 910 doCall false sun.reflect.GeneratedMethodAccessor232 null -1 invoke false sun.reflect.DelegatingMethodAccessorImpl DelegatingMethodAccessorImpl.java 25 invoke false java.lang.reflect.Method Method.java 597 invoke false org.codehaus.groovy.reflection.CachedMethod CachedMethod.java 90 invoke false groovy.lang.MetaMethod MetaMethod.java 233 doMethodInvoke false org.codehaus.groovy.runtime.metaclass.ClosureMetaClass ClosureMetaClass.java 272 invokeMethod false groovy.lang.MetaClassImpl MetaClassImpl.java 885 invokeMethod false org.codehaus.groovy.runtime.callsite.PogoMetaClassSite PogoMetaClassSite.java 66 callCurrent false org.codehaus.groovy.runtime.callsite.AbstractCallSite AbstractCallSite.java 141 callCurrent false groovy.ui.Console$_runScriptImpl_closure16 Console.groovy -1 doCall false sun.reflect.GeneratedMethodAccessor231 null -1 invoke false sun.reflect.DelegatingMethodAccessorImpl DelegatingMethodAccessorImpl.java 25 invoke false java.lang.reflect.Method Method.java 597 invoke false org.codehaus.groovy.reflection.CachedMethod CachedMethod.java 90 invoke false groovy.lang.MetaMethod MetaMethod.java 233 doMethodInvoke false org.codehaus.groovy.runtime.metaclass.ClosureMetaClass ClosureMetaClass.java 272 invokeMethod false groovy.lang.MetaClassImpl MetaClassImpl.java 885 invokeMethod false groovy.lang.Closure Closure.java 405 call false groovy.lang.Closure Closure.java 399 call false groovy.lang.Closure Closure.java 483 run false java.lang.Thread Thread.java 662 run false
Icon and Unicon
This Icon solution uses Unicon extensions. An Icon only version has not been provided.
the following code for buildStackTrace in Utils is taken verbatim and shown below the main program <lang Unicon> import Utils # for buildStackTrace
procedure main()
g() write() f()
end
procedure f()
g()
end
procedure g()
# Using 1 as argument omits the trace of buildStackTrace itself
every write("\t",!buildStackTrace(1))
end</lang>
<lang Unicon>#
- Compute the current stack trace. Starting at level n above
- the current procedure. Here, n defaults to 0, which will
- include this procedure in the stack trace.
- ce defaults to ¤t.
- This only works with newer versions of Unicon!
- <[generates the stacktrace from current call back to first
- in the co-expression]>
procedure buildStackTrace(n:0, # starting distance from this call ce # co-expr to trace stack in [¤t] ) local L /ce := ¤t L := []; n -:= 1 while pName := image(proc(ce, n+:=1)) do { fName := keyword("&file",ce,n) | "no file name" fLine := keyword("&line",ce,n) | "no line number" put(L, pName||" ["||fName||":"||fLine||"]" ) } return L end</lang> The output of this example is:
procedure g [Stacktrace.icn:13]
procedure main [Stacktrace.icn:2]
procedure g [Stacktrace.icn:13]
procedure f [Stacktrace.icn:8]
procedure main [Stacktrace.icn:4]
J
J's stack can be accessed only when suspension has been enabled. When suspension has not been enabled, break points will not work, errors will bubble out to the top level, and the stack data structure will not be available.
To enable suspension and record subsequent stack frames: <lang j> 13!:0]1</lang>
To retrieve a current stack trace: <lang j> 13!:13</lang>
See also: http://www.jsoftware.com/help/dictionary/dx013.htm
Example:
<lang j> f=:g
g=:13!:13 bind f 7 NB. empty stack trace because debugging has not been enabled 13!:0]1 f 7
┌─┬─┬─┬─┬─────────────┬┬───┬──┬─┐ │g│0│0│3│13!:13@("_)││┌─┐│ │ │ │ │ │ │ │ │││7││ │ │ │ │ │ │ │ ││└─┘│ │ │ ├─┼─┼─┼─┼─────────────┼┼───┼──┼─┤ │f│0│0│3│g ││┌─┐│ │ │ │ │ │ │ │ │││7││ │ │ │ │ │ │ │ ││└─┘│ │ │ └─┴─┴─┴─┴─────────────┴┴───┴──┴─┘</lang>
Technical note: the stack trace is not displayed, here, until after the stack has been discarded. This is because we have returned the stack trace as a result and relied on J's implicit display of the result of an expression to display the stack trace.
Java
<lang java5>public class StackTracer {
public static void printStackTrace() {
StackTraceElement[] elems = Thread.currentThread().getStackTrace();
System.out.println("Stack trace:"); for (int i = elems.length-1, j = 2 ; i >= 3 ; i--, j+=2) { System.out.printf("%" + j + "s%s.%s%n", "", elems[i].getClassName(), elems[i].getMethodName()); }
}
}</lang> Demonstration code: <lang java5>public class StackTraceDemo {
static void inner() {
StackTracer.printStackTrace();
}
static void middle() {
inner();
}
static void outer() {
middle();
}
public static void main(String[] args) {
outer();
}
}</lang> Output:
Stack trace:
StackTraceDemo.main
StackTraceDemo.outer
StackTraceDemo.middle
StackTraceDemo.inner
JavaScript
There is no standard way to do this, but some implementations provide it.
<lang javascript>try {
throw new Error;
} catch(e) {
alert(e.stack);
}</lang>
The following version works in many browsers but it infinitely loops when there is recursion: <lang javascript>function foo () {
var stack = "Stack trace:";
for (var f = arguments.callee // current function
; f; f = f.caller) {
stack += "\n" + f.name;
}
alert(stack);
} foo();</lang>
Lasso
By default Lasso tracks the file path, line and column numbers. You can create a trace method to track type and method names illustrated below or use one of the public libraries like L-Debug [1].
<lang Lasso>// Define our own trace method define trace => {
local(gb) = givenblock
// Set a depth counter
var(::_tracedepth)->isnota(::integer) ? $_tracedepth = 0
handle => {$_tracedepth--}
// Only output when supplied a capture
#gb ? stdoutnl(
// Indent
('\t' * $_tracedepth++) +
// Type + Method
#gb->self->type + '.' + #gb->calledname +
// Call site file
': ' + #gb->home->callsite_file +
// Line number and column number
' (line '+#gb->home->callsite_line + ', col ' + #gb->home->callsite_col +')'
)
return #gb()
}</lang>
- Use Trace
<lang Lasso>define stackexample => type {
public oncreate => trace => { return self }
public inner => trace => { }
public middle => trace => { .inner }
public outer => trace => { .middle }
}
stackexample->outer</lang>
- Output:
stackexample.oncreate: adminapp_lasso_runner_thread (line 2, col 24) stackexample.outer: adminapp_lasso_runner_thread (line 5, col 21) stackexample.middle: adminapp_lasso_runner_thread (line 4, col 22) stackexample.inner: adminapp_lasso_runner_thread (line 3, col 21)
Lua
<lang lua>function Inner( k )
print( debug.traceback() ) print "Program continues..."
end
function Middle( x, y )
Inner( x+y )
end
function Outer( a, b, c )
Middle( a*b, c )
end
Outer( 2, 3, 5 )</lang>
stack traceback: ./prog:4: in function 'Inner' ./prog:9: in function 'Middle' ./prog:13: in function 'Outer' ./prog:16: in main chunk [C]: ? Program continues...
Mathematica
Built-in function Stack does the task, example I: <lang Mathematica>f[g[1, Print[Stack[]]; 2]]</lang> prints, gives back: <lang Mathematica>{f,g,CompoundExpression,Print} f[g[1, 2]]</lang> Example II: <lang Mathematica>f[g[1, Print[Stack[_]]; 2]]</lang> prints, gives back: <lang Mathematica>{f[g[1,Print[Stack[_]];2]],g[1,Print[Stack[_]];2],Print[Stack[_]];2,Print[Stack[_]]} f[g[1, 2]]</lang> Related and similar functions are: Trace, TracePrint, TraceScan,TraceDialog, Monitor, StackInhibit, StackBegin, StackComplete. In the manual look for 'guide/SymbolicExecutionHistory'.
NetRexx
<lang NetRexx>/* NetRexx */ options replace format comments java crossref symbols nobinary
class RStackTraces
method inner() static StackTracer.printStackTrace() method middle() static inner() method outer() static middle() method main(args = String[]) public static outer()
class RStackTraces.StackTracer
method printStackTrace() public static
elems = Thread.currentThread().getStackTrace()
say 'Stack trace:'
j_ = 2
loop i_ = elems.length - 1 to 2 by -1
say .left(j_) || elems[i_].getClassName()'.'elems[i_].getMethodName()
j_ = j_ + 2
end i_
</lang> Output:
Stack trace:
RStackTraces.main
RStackTraces.outer
RStackTraces.middle
RStackTraces.inner
Objective-C
<lang objc>#include <execinfo.h>
void *frames[128]; int len = backtrace(frames, 128); char **symbols = backtrace_symbols(frames, len); for (int i = 0; i < len; ++i) {
NSLog(@"%s", symbols[i]);
} free(symbols);</lang>
Or in Mac OS X 10.6+: <lang objc>NSArray *symbols = [NSThread callStackSymbols]; for (NSString *symbol in symbols) {
NSLog(@"%@", symbol);
}</lang>
OCaml
<lang ocaml>let div a b = a / b
let () =
try let _ = div 3 0 in () with e -> prerr_endline(Printexc.to_string e); Printexc.print_backtrace stderr;
- </lang>
outputs:
Division_by_zero Raised by primitive operation at file "test.ml", line 4, characters 14-21
By Environment Variable
Another way is to set the environment variable OCAMLRUNPARAM to b, for example you can add in your ~/.bashrc file this line:
export OCAMLRUNPARAM='b'
Then the code doesn't need additional statements: <lang ocaml>let div a b = a / b
let () =
let _ = div 3 0 in ()
- </lang>
outputs:
Fatal error: exception Division_by_zero Raised at file "test.ml", line 4, characters 10-17
Oforth
Stack trace is only available :
1) When an exception is raised
2) And when oforth debug level is at least 1, using --D command line option (oforth --D1)
Otherwise no stack trace is available nor printed.
<lang Oforth>func: f1 { Exception throw("An exception") } Integer method: f2 { self f1 } func: f3(n) { n f2 } func: f4(n) { n f3 }
f4(10)</lang>
- Output:
[1:interpreter] Exception : An exception Into Method #throw self = (Exception) An exception Into Method #throw self = (Class) Exception Into Function #f1 Into Method #f2 self = (Integer) 10 Into Function #f3
OxygenBasic
<lang oxygenbasic> '32bit x86
static string Report
macro ReportStack(n)
'===================
' scope ' static sys stack[0X100],stackptr,e ' 'CAPTURE IMAGE OF UP TO 256 ENTRIES ' ' mov eax,n cmp eax,0x100 ( jle exit mov eax,0x100 'UPPER LIMIT ) mov e,eax mov stackptr,esp lea edx,stack mov ecx,e mov esi,esp ( mov eax,[esi] mov [edx],eax add esi,4 add edx,4 dec ecx jg repeat ) sys i string cr=chr(13)+chr(10), tab=chr(9) ' for i=1 to e report+=hex(stackptr+(i-1)*4,8) tab hex(i-1,2) tab hex(stack[i],8) cr next ' end scope '
end macro
'==== 'TEST '====
function foo() '=============
push 0x44556677 push 0x33445566 push 0x22334455 push 0x11223344 ReportStack(8)
end function
Report+="Trace inside foo " foo() print report 'putfile "s.txt",Report
/* RESULT:
Trace inside foo 0017FE00 00 11223344 0017FE04 01 22334455 0017FE08 02 33445566 0017FE0C 03 44556677 0017FE10 04 005EAB1C 0017FE14 05 0017FE40 0017FE18 06 10002D5F 0017FE1C 07 00000000
- /
</lang>
Oz
System exceptions contain the current stack at the nested feature debug.stack. For example:
<lang oz>declare
proc {Test}
_ = 1 div 0
end
in
try
{Test}
catch E then
{Inspect E}
end</lang>
Output:
To have such a stack trace in custom exceptions, either indicate this by throwing a record value with a debug:unit feature or use the Exception module to create exceptions.
To access the stack trace directly, you can use the undocumented internal Debug module. Its getTaskStack function takes a thread, a depth value and a boolean "verbose" flag. It returns a list of stack frames. Example:
<lang oz>%% make sure that simple function calls are not optimized away
\switch +controlflowinfo
declare
[Debug] = {Link ['x-oz://boot/Debug']}
proc {F} {G} end
proc {G} {H} end
proc {H}
{Inspect {Debug.getTaskStack {Thread.this} 100 true}}
end
in
{F}</lang>
Output:
Nim
In (normal) debug builds stacktraces are enabled, while in release builds stacktraces are disabled by default, but can be enabled like this: nim c -d:release --stacktrace:on --linetrace:on file.nim
<lang nim>proc g() =
writeStackTrace()
proc f() =
g()
f()</lang>
Perl
<lang perl>use Carp 'cluck';
sub g {cluck 'Hello from &g';} sub f {g;}
f;</lang>
This prints:
Hello from &g at Print a Stack Trace line 3 main::g() called at Print a Stack Trace line 4 main::f() called at Print a Stack Trace line 6
Perl 6
<lang perl6>sub g { say Backtrace.new.concise } sub f { g } sub MAIN { f }</lang>
- Output:
in sub g at bt:1 in sub f at bt:2 in sub MAIN at bt:3
PHP
<lang php><?php class StackTraceDemo {
static function inner() {
debug_print_backtrace();
}
static function middle() {
self::inner();
}
static function outer() {
self::middle();
}
}
StackTraceDemo::outer(); ?></lang>
#0 StackTraceDemo::inner() called at [/home/cweiske/Dev/cvs/test/php-stacktrace.php:7] #1 StackTraceDemo::middle() called at [/home/cweiske/Dev/cvs/test/php-stacktrace.php:10] #2 StackTraceDemo::outer() called at [/home/cweiske/Dev/cvs/test/php-stacktrace.php:14]
PL/I
<lang PL/I> /* The SNAP option in the ON statement is sufficient to obtain */ /* a traceback. The SYSTEM option specifies that standard */ /* system action is to occur, which resume execution after the */ /* SIGNAL statement. */ on condition(traceback) snap system; ... signal condition(traceback); </lang>
PicoLisp
PicoLisp doesn't keep full backtrace information at runtime. This is for performance reasons. However, existing variable bindings (environments) can be inspected with the 'env' function, so this can be used to build your own stack frames.
The following is analog to (though simpler than) the built-in 'trace' mechanism. The function '$$' (corresponds to '$' for tracing) is inserted by 'stackAll' into every function and method definition (corresponds to 'traceAll'). Then, when stopping at a 'debug' breakpoint or an error handler, 'dumpStack' can be used to inspect the stack contents.
As this mechanism uses 'let' to hold the stack frames, it is robust also across catch/throw, coroutines and error handling. <lang PicoLisp>(off "Stack")
(de $$ "Prg"
(let "Stack" (cons (cons (car "Prg") (env)) "Stack") # Build stack frame
(set "Stack"
(delq (asoq '"Stack" (car "Stack")) # Remove self-created entries
(delq (asoq '"Prg" (car "Stack"))
(car "Stack") ) ) )
(run (cdr "Prg")) ) ) # Run body
(de stackAll (Excl)
(let *Dbg NIL
(for "X" (all)
(or
(memq "X" Excl)
(memq "X" '($$ @ @@ @@@))
(= `(char "*") (char "X"))
(cond
((= `(char "+") (char "X"))
(for "Y" (pair (val "X"))
(and
(pair "Y")
(fun? (cdr "Y"))
(unless (== '$$ (caaddr "Y"))
(con (cdr "Y")
(list
(cons '$$ (cons (car "Y" "X") (cddr "Y"))) ) ) ) ) ) )
((pair (getd "X"))
(let "Y" @
(unless (== '$$ (caadr "Y"))
(con "Y"
(list (cons '$$ "X" (cdr "Y"))) ) ) ) ) ) ) ) ) )
(de dumpStack ()
(more (reverse (cdr "Stack"))) T )</lang>
Test: <lang PicoLisp>(de foo (A B)
(let C 3
(bar (inc 'A) (inc 'B) (inc 'C)) ) )
(de bar (A D E)
(let (A 7 B 8 C 9)
(! println A B C) ) ) # Set a breakpoint before (println A B C)
(stackAll)</lang>
: (foo 1 2) # Call 'foo' (println A B C) # Stopped at breakpoint in 'bar' ! (dumpStack) # Dump stack history (foo (A . 1) (B . 2) (@ . T)) # Hit <enter> on each line to continue (bar (B . 3) (C . 4) (A . 2) (D . 3) (E . 4) (@ . T)) -> T ! # Hit <enter> to continue execution 7 8 9 # Output of (println A B C) -> 9 :
PureBasic
The ShowCallstack()command opens a interactive display allowing viewing of the procedures in the calling path an all their local variables. <lang PureBasic>Procedure Three()
a=7 ShowCallstack() CallDebugger
EndProcedure
Procedure Two()
a=4 Three()
EndProcedure
Procedure One()
a=2 Two()
EndProcedure
One()</lang>
Python
See the traceback module <lang python>import traceback
def f(): return g() def g(): traceback.print_stack()
f()</lang>
Sample output from a session in the Idle IDE:
File "<string>", line 1, in <module>
File "C:\Python26\lib\idlelib\run.py", line 93, in main
ret = method(*args, **kwargs)
File "C:\Python26\lib\idlelib\run.py", line 293, in runcode
exec code in self.locals
File "C:/Documents and Settings/All Users/Documents/Paddys/traceback.py", line 6, in <module>
f()
File "C:/Documents and Settings/All Users/Documents/Paddys/traceback.py", line 3, in f
def f(): return g()
File "C:/Documents and Settings/All Users/Documents/Paddys/traceback.py", line 4, in g
def g(): traceback.print_stack()
R
<lang R>foo <- function() {
bar <- function()
{
sys.calls()
}
bar()
}
foo()</lang>
[[1]] foo() [[2]] bar()
traceback() returns the callstack of the last unhandled (i.e. not in try/catch) error.
You can also see the stack trace when a function is called (or as it exits) using the trace function. <lang R>trace("foo", recover) foo()</lang>
Tracing foo() on entry Enter a frame number, or 0 to exit 1: foo() Selection:
Racket
<lang Racket>
- lang racket
- To see these calls we do two things
- mutate the binding to prevent
- Racket from inlining the value; use a (void) call at the end so the
- calls are not tail calls (which will otherwise not show on the
- stack).
(define foo #f) (set! foo (λ() (bar) (void))) (define bar #f) (set! bar (λ() (show-stacktrace) (void)))
(define (show-stacktrace)
(for ([s (continuation-mark-set->context (current-continuation-marks))]
[i (in-naturals)])
;; show just the names, not the full source information
(when (car s) (printf "~s: ~s\n" i (car s)))))
(foo) </lang>
Output:
0: show-stacktrace 1: bar 2: foo 3: |[running body]|
Raven
<lang Raven> [1 2 3 4] 42 { 'a' 1 'b' 2 'c' 3 } 34.1234 ( -1 -2 -3 ) "The quick brown fox" FILE dump</lang>
- Output:
hash (4 items) usage => 1 index => 65836 flags => 256 buffer => " 98252f8 73 74 64 69 6e 00 stdin." The quick brown fox 28.1234 hash (3 items) a => 1 b => 2 c => 3 42 list (4 items) 0 => 1 1 => 2 2 => 3 3 => 4
Ruby
<lang ruby>def outer(a,b,c)
middle a+b, b+c
end
def middle(d,e)
inner d+e
end
def inner(f)
puts caller(0)
puts "continuing... my arg is #{f}"
end
outer 2,3,5</lang>
$ ruby stacktrace.rb stacktrace.rb:10:in `inner' stacktrace.rb:6:in `middle' stacktrace.rb:2:in `outer' stacktrace.rb:14 continuing... my arg is 13
Exceptions caught in a rescue clause contain the trace information: <lang ruby>def outer(a,b,c)
middle a+b, b+c
end
def middle(d,e)
inner d+e
end
def inner(f)
raise puts "this will not be printed"
end
begin
outer 2,3,5
rescue Exception => e
puts e.backtrace
end puts "continuing after the rescue..."</lang>
stacktrace.rb:10:in `inner' stacktrace.rb:6:in `middle' stacktrace.rb:2:in `outer' stacktrace.rb:15 continuing after the rescue...
Thread has a backtrace method: <lang ruby>p Thread.current.backtrace</lang>
Scala
While the code on the Java example works with Scala too, the code below is an alternative. Which, by the way, could be used from Java as well, with minor modifications.
<lang scala>def callStack = try { error("exception") } catch { case ex => ex.getStackTrace drop 2 }
def printStackTrace = callStack drop 1 /* don't print ourselves! */ foreach println</lang>
Usage example:
scala> def f1 = printStackTrace f1: Unit scala> def f2 = f1 f2: Unit scala> def f3 = f2 f3: Unit scala> f3 line40$object$$iw$$iw$.f1(<console>:6) line41$object$$iw$$iw$.f2(<console>:7) line42$object$$iw$$iw$.f3(<console>:8) line43$object$$iw$$iw$.<init>(<console>:10) line43$object$$iw$$iw$.<clinit>(<console>) RequestResult$line43$object$.<init>(<console>:4) RequestResult$line43$object$.<clinit>(<console>) RequestResult$line43$object.result(<console>) sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) java.lang.reflect.Method.invoke(Method.java:597) scala.tools.nsc.Interpreter$Request$$anonfun$loadAndRun$1$$anonfun$apply$13.apply(Interpreter.scala:788) scala.tools.nsc.Interpreter$Request$$anonfun$loadAndRun$1$$anonfun$apply$13.apply(Interpreter.scala:788) scala.util.control.Exception$Catch.apply(Exception.scala:79) scala.tools.nsc.Interpreter$Request$$anonfun$loadAndRun$1.apply(Interpreter.scala:787) scala.tools.nsc.Interpreter$Request$$anonfun$loadAndRun$1.apply(Interpreter.scala:787) scala.util.control.Exception$Catch.apply(Exception.scala:79) scala.tools.nsc.Interpreter$Request.loadAndRun(Interpreter.scala:786) scala.tools.nsc.Interpreter.interpret(Interpreter.scala:435) scala.tools.nsc.Interpreter.interpret(Interpreter.scala:425) scala.tools.nsc.InterpreterLoop.interpretStartingWith(InterpreterLoop.scala:331) scala.tools.nsc.InterpreterLoop.command(InterpreterLoop.scala:308) scala.tools.nsc.InterpreterLoop.processLine$1(InterpreterLoop.scala:205) scala.tools.nsc.InterpreterLoop.repl(InterpreterLoop.scala:223) scala.tools.nsc.InterpreterLoop.main(InterpreterLoop.scala:379) scala.tools.nsc.MainGenericRunner$.createLoop$1(MainGenericRunner.scala:119) scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:144) scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)
Note that the stack is an array of StackTraceElement, on which it is possible to get the class and method name as well as the file name and line number of its definition.
Slate
The following #printCurrentStack is already defined in the base slate image but it is replicated here.
<lang slate>slate[1]> d@(Debugger traits) printCurrentStack &limit: limit &stream: out &showLocation: showLocation [
d clone `>> [baseFramePointer: (d interpreter framePointerOf: #printCurrentStack).
buildFrames.
printBacktrace &limit: limit &stream: out &showLocation: showLocation ]
]. Defining function 'printCurrentStack' on: 'Debugger traits' [printCurrentStack &limit: &stream: &showLocation:]</lang>
The output from calling the function:
<lang slate>slate[2]> Debugger printCurrentStack. Backtrace (method @ source): frame: 0 [printCurrentStack &limit: &stream: &showLocation:] @ stdin:0 frame: 1 [evaluateIn: &optionals:] @ src/mobius/syntax.slate:180 frame: 2 [(arity: 0)] @ src/lib/repl.slate:155 frame: 3 [on:do:] @ src/core/condition.slate:43 frame: 4 [(arity: 0)] @ src/lib/repl.slate:147 frame: 5 [handlingCases:] @ src/core/condition.slate:64 frame: 6 [interpretHook:] @ src/lib/repl.slate:42 frame: 7 [(arity: 0)] @ src/lib/repl.slate:139 frame: 8 [enter] @ src/lib/repl.slate:135 frame: 9 [start &resource:] @ src/lib/repl.slate:185 frame: 10 [start] @ src/mobius/prelude.slate:38 Nil</lang>
Smalltalk
A backtrace is normally sent when some error occurs; however, it can be "forced":
<lang smalltalk>Object subclass: Container [
Container class >> outer: a and: b and: c [
self middle: (a+b) and: (b+c)
]
Container class >> middle: x and: y [
self inner: (x*y)
]
Container class >> inner: k [
Smalltalk backtrace
]
].
Container outer: 2 and: 3 and: 5.
'Anyway, we continue with it' displayNl.</lang>
Output:
Container class>>inner: Container class>>middle:and: Container class>>outer:and:and: UndefinedObject>>executeStatements Anyway, we continue with it
Tcl
<lang tcl>proc printStackTrace {} {
puts "Stack trace:"
for {set i 1} {$i < [info level]} {incr i} {
puts [string repeat " " $i][info level $i]
}
}</lang> Demonstration code: <lang tcl>proc outer {a b c} {
middle [expr {$a+$b}] [expr {$b+$c}]
} proc middle {x y} {
inner [expr {$x*$y}]
} proc inner k {
printStackTrace
} outer 2 3 5</lang> Produces this output:
Stack trace:
outer 2 3 5
middle 5 8
inner 40
zkl
<lang zkl>fcn f{println("F");vm.stackTrace().println()} fcn g{println("G")} f();g();</lang>
- Output:
stackTrace just returns a string. You don't get to futz with the stack.
F Stack trace for VM#1 (): Cmd.f@stackTrace addr:4 args(0) reg(0) Cmd.__constructor addr:3 args(0) reg(0) R startup.__constructor addr:2242 args(0) reg(1) ER startup.__constructor addr:2178 args(0) reg(22) G
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