Reverse a string

Take a string and reverse it. For example, "asdf" becomes "fdsa".

For extra credit, preserve Unicode combining characters. For example, "as⃝df̅" becomes "f̅ds⃝a", not "̅fd⃝sa".

ActionScript

<lang ActionScript>function reverseString(string:String):String { var reversed:String = new String(); for(var i:int = string.length -1; i >= 0; i--) reversed += string.charAt(i); return reversed; }

function reverseStringCQAlternative(string:String):String { return string.split().reverse().join(); } </lang>

ALGOL 68

Works with: ALGOL 68 version Standard - no extensions to language used

Works with: ALGOL 68G version Any - tested with release mk15-0.8b.fc9.i386

Works with: ELLA ALGOL 68 version Any (with appropriate job cards) - tested with release 1.8.8d.fc9.i386

<lang algol68>PROC reverse = (REF STRING s)VOID:

 FOR i TO UPB s OVER 2 DO
   CHAR c = s[i];
   s[i] := s[UPB s - i + 1];
   s[UPB s - i + 1] := c
 OD;

main: (

 STRING text := "Was it a cat I saw";
 reverse(text);
 print((text, new line))

)</lang> Output:

was I tac a ti saW

AppleScript

<lang AppleScript>get reverse_string("as⃝df̅")

on reverse_string(str) set old_delim to (get AppleScript's text item delimiters) set AppleScript's text item delimiters to ""

set temp to (reverse of text items of str) set temp to (text items of temp) as Unicode text

set AppleScript's text item delimiters to old_delim return temp end reverse_string</lang>

AutoIt

<lang AutoIt>#AutoIt Version: 3.2.10.0 $mystring="asdf" $reverse_string = "" $string_length = StringLen($mystring)

For $i = 1 to $string_length

  $last_n_chrs = StringRight($mystring, $i)
  $nth_chr = StringTrimRight($last_n_chrs, $i-1)
  $reverse_string= $reverse_string & $nth_chr

Batch File

<lang dos>@echo off setlocal enabledelayedexpansion call :reverse %1 res echo %res% goto :eof

reverse

set str=%~1 set cnt=0

loop

if "%str%" equ "" ( goto :eof ) set chr=!str:~0,1! set str=%str:~1% set %2=%chr%!%2! goto loop</lang>

BBC BASIC

<lang bbcbasic> PRINT FNreverse("The five boxing wizards jump quickly")

     END
     
     DEF FNreverse(A$)
     LOCAL B$, C%
     FOR C% = LEN(A$) TO 1 STEP -1
       B$ += MID$(A$,C%,1)
     NEXT
     = B$</lang>

Befunge

To see this in action, it's best to use an interpreter that animates the process.

<lang befunge>v The string to reverse. The row to copy to.

  |                      | The actual copying happens here.
  |                      | |    Increment column to write to.
  |                      | |    |  Store column #.
  v                      v v    v  v

> "reverse me" 3 10p >10g 4 p 10g1+ 10pv

              ^ ^   |:                <

First column --| | @ ^ to write to. | ^ Get the address

  All calls to 10   |  to copy the next
involve saving or   |  character to.
      reading the   End when stack is empty or
  column to write   explicit zero is reached.
              to.</lang>

Bracmat

<lang>

 ( reverse
 = L x
   .     :?L
       & @( !arg
          :   ?
              ( %?x
              & utf$!x
              & !x !L:?L
              & ~`
              )
              ?
          )
     | str$!L
 )

& out$reverse$Ελληνικά </lang> Result: <lang>άκινηλλΕ</lang>

Brainf***

The former wont stop taking input bytes unless a special compiler was made to stop at ENTER. The following checks for 10 ascii (line feed) and stops taking input at that point

<lang bf>,----- ----- [+++++ +++++ > , ----- -----] If a newline is hit counter will be zero and input loop ends <[.<] run all chars backwards and print them

just because it looks good we print CRLF +++++ +++++ +++ . --- .</lang>

Brat

<lang brat>p "olleh".reverse #Prints "hello"</lang>

C

<lang c>#include <stdio.h>

include <stdlib.h>
include <locale.h>
include <wchar.h>

char *sa = "abcdef"; char *su = "as⃝df̅"; /* Should be in your native locale encoding. Mine is UTF-8 */

int is_comb(wchar_t c) { if (c >= 0x300 && c <= 0x36f) return 1; if (c >= 0x1dc0 && c <= 0x1dff) return 1; if (c >= 0x20d0 && c <= 0x20ff) return 1; if (c >= 0xfe20 && c <= 0xfe2f) return 1; return 0; }

wchar_t* mb_to_wchar(char *s) { wchar_t *u; size_t len = mbstowcs(0, s, 0) + 1; if (!len) return 0;

u = malloc(sizeof(wchar_t) * len); mbstowcs(u, s, len); return u; }

wchar_t* ws_reverse(wchar_t* u) { size_t len, i, j; wchar_t *out; for (len = 0; u[len]; len++); out = malloc(sizeof(wchar_t) * (len + 1)); out[len] = 0; j = 0; while (len) { for (i = len - 1; i && is_comb(u[i]); i--); wcsncpy(out + j, u + i, len - i); j += len - i; len = i; } return out; }

char *mb_reverse(char *in) { size_t len; char *out; wchar_t *u = mb_to_wchar(in); wchar_t *r = ws_reverse(u); len = wcstombs(0, r, 0) + 1; out = malloc(len); wcstombs(out, r, len); free(u); free(r); return out; }

int main(void) { setlocale(LC_CTYPE, "");

printf("%s => %s\n", sa, mb_reverse(sa)); printf("%s => %s\n", su, mb_reverse(su)); return 0; }</lang>output<lang>abcdef => fedcba as⃝df̅ => f̅ds⃝a</lang>

C++

<lang cpp>#include <iostream>

include <string>
include <algorithm>

int main() {

 std::string s;
 std::getline(std::cin, s);
 std::reverse(s.begin(), s.end()); // modifies s
 std::cout << s << std::endl;
 return 0;

}</lang>

C#

C# does not have a built-in Reverse method for strings, which are immutable. One way to implement this is to convert the string to an array of characters, reverse that, and return a new string from the reversed array: <lang csharp>private static string ReverseString(string input) { char[] inputChars = input.ToCharArray(); Array.Reverse(inputChars); return new string(inputChars); }</lang>

As of C# 4.0 you can call the Reverse method on a string, however it returns an Enumerable of chars. It appears that this only helps by letting you do the above in a different order (reverse the string, convert that to an array of chars, and return a new string from the reversed array):

<lang csharp>return new string(input.Reverse().ToArray());</lang>

Clojure

Basic reverse

For normal strings, the reverse function can be used to do the bulk of the work. However, it returns a character sequence, which has to be converted back to a string.

<lang lisp>(defn str-reverse [s] (apply str (reverse s)))</lang>

Reverse words in a string

<lang lisp>(apply str (interpose " " (reverse (.split "the quick brown fox" " "))))</lang>

Supporting combining characters

Handling combining characters present a trickier task. We need to protect the relative ordering of the combining character and the character to its left. Thus, before reversing, the characters need to be grouped.

<lang lisp>(defn combining? [c]

 (let [type (Character/getType c)]
   ;; currently hardcoded to the types taken from the sample string
   (or (= type 6) (= type 7))))

(defn group

 "Group normal characters with their combining characters"
 [chars]
 (cond (empty? chars) chars

(empty? (next chars)) (list chars) :else (let [dres (group (next chars))] (cond (combining? (second chars)) (cons (cons (first chars) (first dres)) (rest dres)) :else (cons (list (first chars)) dres)))))

(defn str-reverse

 "Unicode-safe string reverse"
 [s]
 (apply str (apply concat (reverse (group s)))))</lang>

And the test result:

user=> s
"as⃝df̅"
user=> (str-reverse s)
"f̅ds⃝a"[
user=> (str-reverse (str-reverse s))
"as⃝df̅"
user=>

CoffeeScript

<lang javascript> "qwerty".split("").reverse().join "" </lang>

ColdFusion

You can reverse anything that can be written to the document in hashmarks (i.e. strings, numbers, now( ), etc.). <lang cfm><cfset myString = "asdf" /> <cfset myString = reverse( myString ) /></lang>

Common Lisp

<lang lisp>(reverse my-string)</lang>

D

<lang d>import std.stdio, std.range, std.conv;

void main() {

   string s1 = "hello"; // UTF-8
   string s1r = text(retro("hello"));
   assert(s1r == "olleh");

   wstring s2 = "hello"w; // UTF-16
   wstring s2r = wtext(retro("hello"));
   assert(s2r == "olleh");

   dstring s3 = "hello"d; // UTF-32
   dstring s3r = dtext(retro("hello"));
   assert(s3r == "olleh");

}</lang>

Dart

Dart apparently has no String or List reverse method <lang dart>String reverse(String s) {

 StringBuffer sb=new StringBuffer();
 for(int i=s.length-1;i>=0;i--) {
   sb.add(s[i]);
 }
 return sb.toString();

}

main() {

 print(reverse('a string.'));

}</lang>

Delphi

<lang Delphi> function ReverseString(const InString: string): string; var

 i: integer;

begin

 for i := Length(InString) downto 1 do
   Result := Result + InString[i];

end; </lang>

You could also use this RTL function Introduced in Delphi 6:

<lang Delphi>StrUtils.ReverseString</lang>

DWScript

See Delphi.

E

<lang e>pragma.enable("accumulator") def reverse(string) {

 return accum "" for i in (0..!(string.size())).descending() { _ + string[i] }

}</lang>

Emacs Lisp

<lang lisp> (concat (reverse (append "Hello World" nil))) </lang>

Output:

"dlroW olleH"

Eiffel

<lang eiffel>class

   APPLICATION

create

   make

feature

   make
           -- Demonstrate string reversal.
       do
           my_string := "Hello World!"
           my_string.mirror
           print (my_string)
       end
   my_string: STRING
           -- Used for reversal

end</lang>

Output:

!dlroW olleH

Erlang

<lang erlang>1> lists:reverse("reverse!"). "!esrever"</lang>

Erlang also supports binary strings, which uses its binary format. There is no standard function to reverse a binary sequence, but the following one does the job well enough. It works by changing the endianness (from little to big or the opposite) of the whole sequence, effectively reversing the string. <lang erlang>reverse(Bin) ->

   Size = size(Bin)*8,
   <<T:Size/integer-little>> = Bin,
   <<T:Size/integer-big>>.</lang>

Result:

1> test:reverse(<<"hello">>).
<<"olleh">>

Euphoria

<lang euphoria> include std/sequence.e printf(1, "%s\n", {reverse("abcdef") }) </lang>

F#

<lang fsharp>let ReverseString (s:string) = new string(Array.rev (s.ToCharArray()))</lang>

Factor

A string is a sequence and there is a default reverse implementation for those. <lang factor>"hello" reverse</lang> string-reverse preserves graphemes: <lang factor>"as⃝df̅" string-reverse "f̅ds⃝a" = .</lang>

Fancy

<lang fancy>"hello world!" reverse</lang>

Forth

<lang forth>: exchange ( a1 a2 -- )

 2dup c@ swap c@ rot c! swap c! ;

reverse ( c-addr u -- )

 1- bounds begin 2dup > while
   2dup exchange
   -1 /string
 repeat 2drop ;

s" testing" 2dup reverse type \ gnitset</lang>

Fortran

Works with: Fortran version 90 and later

<lang fortran>PROGRAM Example

 CHARACTER(80) :: str = "This is a string"
 CHARACTER :: temp
 INTEGER :: i, length

 WRITE (*,*) str
 length = LEN_TRIM(str) ! Ignores trailing blanks. Use LEN(str) to reverse those as well
 DO i = 1, length/2
    temp = str(i:i)
    str(i:i) = str(length+1-i:length+1-i)
    str(length+1-i:length+1-i) = temp
 END DO
 WRITE(*,*) str

END PROGRAM Example</lang> Output:

This is a string
gnirts a si sihT

Another implementation that uses a recursive not-in-place algorithm: <lang fortran>program reverse_string

 implicit none
 character (*), parameter :: string = 'no devil lived on'

 write (*, '(a)') string
 write (*, '(a)') reverse (string)

contains

 recursive function reverse (string) result (res)

   implicit none
   character (*), intent (in) :: string
   character (len (string)) :: res

   if (len (string) == 0) then
     res = 
   else
     res = string (len (string) :) // reverse (string (: len (string) - 1))
   end if

 end function reverse

end program reverse_string</lang> Output: <lang>no devil lived on no devil lived on</lang>

Frink

The built-in reverse function reverses a string or the elements of a list. <lang frink> println[reverse["abcdef"]] </lang>

GAP

<lang gap>Reversed("abcdef");

"fedcba"</lang>

Gema

Reverse each line in the input stream. Using built in function: <lang gema>\L=@reverse{$1}</lang> Not using built in function (recursively apply substring to same rule): <lang gema>\L<U1>=@{$2}$1</lang>

Go

Functions below assume UTF-8 encoding. (The task mentions Unicode but does not specify an encoding.) Strings in Go are not restricted to be UTF-8, but Go has good support for it and works with UTF-8 most natually. As shown below, certain string conversions work in UTF-8 and the range clause over a string works in UTF-8. Go also has a Unicode package in the standard library that makes easy work of recognizing combining characters for this task. <lang go>package main

import (

   "fmt"
   "unicode"
   "unicode/utf8"

)

// no encoding func reverseBytes(s string) string {

   r := make([]byte, len(s))
   for i := 0; i < len(s); i++ {
       r[i] = s[len(s)-1-i]
   }
   return string(r)

}

// reverseCodePoints interprets its argument as UTF-8 and ignores bytes // that do not form valid UTF-8. return value is UTF-8. func reverseCodePoints(s string) string {

   r := make([]rune, len(s))
   start := len(s)
   for _, c := range s {
       // quietly skip invalid UTF-8
       if c != utf8.RuneError {
           start--
           r[start] = c
       }
   }
   return string(r[start:])

}

// reversePreservingCombiningCharacters interprets its argument as UTF-8 // and ignores bytes that do not form valid UTF-8. return value is UTF-8. func reversePreservingCombiningCharacters(s string) string {

   if s == "" {
       return ""
   }
   p := []rune(s)
   r := make([]rune, len(p))
   start := len(r)
   for i := 0; i < len(p); {
       // quietly skip invalid UTF-8
       if p[i] == utf8.RuneError {
           i++
           continue
       }
       j := i + 1
       for j < len(p) && (unicode.Is(unicode.Mn, p[j]) ||
           unicode.Is(unicode.Me, p[j]) || unicode.Is(unicode.Mc, p[j])) {
           j++
       }
       for k := j - 1; k >= i; k-- {
           start--
           r[start] = p[k]
       }
       i = j
   }
   return (string(r[start:]))

}

func main() {

   test("asdf")
   test("as⃝df̅")

}

func test(s string) {

   fmt.Println("\noriginal:      ", []byte(s), s)
   r := reverseBytes(s)
   fmt.Println("reversed bytes:", []byte(r), r)
   fmt.Println("original code points:", []rune(s), s)
   r = reverseCodePoints(s)
   fmt.Println("reversed code points:", []rune(r), r)
   r = reversePreservingCombiningCharacters(s)
   fmt.Println("combining characters:", []rune(r), r)

}</lang> Output:

original:       [97 115 100 102] asdf
reversed bytes: [102 100 115 97] fdsa
original code points: [97 115 100 102] asdf
reversed code points: [102 100 115 97] fdsa
combining characters: [102 100 115 97] fdsa

original:       [97 115 226 131 157 100 102 204 133] as⃝df̅
reversed bytes: [133 204 102 100 157 131 226 115 97] ��fd���sa
original code points: [97 115 8413 100 102 773] as⃝df̅
reversed code points: [773 102 100 8413 115 97] ̅fd⃝sa
combining characters: [102 773 100 115 8413 97] f̅ds⃝a

Groovy

Solution: <lang groovy>println "Able was I, 'ere I saw Elba.".reverse()</lang> Output:

.ablE was I ere' ,I saw elbA

Haskell

<lang haskell>reverse = foldl (flip (:)) []</lang> This function as defined in the Haskell Prelude.

Supporting combining characters

<lang haskell>import Data.Char (isMark) import Data.List (groupBy) myReverse = concat . reverse . groupBy (const isMark)</lang>

groupBy (const isMark) is an unusual way of splitting a string into its combined characters

HicEst

<lang hicest>CHARACTER string = "Hello World", tmp

L = LEN( string ) DO i = 1, L/2

 tmp = string(i)
 string(i) = string(L-i+1)
 string(L-i+1) = tmp

ENDDO

WRITE(Messagebox, Name) string </lang>

Icon and Unicon

<lang Icon>procedure main(arglist) s := \arglist[1] | "asdf" write(s," <-> ", reverse(s)) # reverse is built-in end</lang>

Io

<lang io>"asdf" reverse</lang>

J

Reverse (|.) reverses a list of items (of any shape or type). <lang j> |.'asdf' fdsa</lang>

Extra credit: First, a function to determine whether a Unicode character is a combining character: <lang j> ranges=.16b02ff 16b036f, 16b1dbf 16b1dff, 16b20cf 16b20ff, 16bfe1f 16bfe2f

  iscombining=. 2 | ranges&I.</lang>

Then we need to box groups of letters and combining characters, reverse, and unbox. The boxing function can be carried out easily with dyad cut, which uses the indices of the ones on the right as the starting points for groups of characters. For clarity, its inverse will be defined as raze, which simply runs together the items inside boxes of its argument. <lang j> split=. (<;.1~ -.@iscombining) :. ;</lang>

After this, the solution is just to reverse under the split transformation. This also takes place under J code to convert from Unicode to integers. <lang j> |.&.split&.(3 u: 7&u:) 'as⃝df̅' f̅ds⃝a</lang>

Java

<lang java>public static String reverseString(String s) {

   return new StringBuffer(s).reverse().toString();

}</lang>

Works with: Java version 1.5+

<lang java5>public static String reverseString(String s) {

   return new StringBuilder(s).reverse().toString();

}</lang>

JavaScript

<lang javascript>var a = "cat".split(""); a.reverse(); print(a.join("")); // tac</lang>

LabVIEW

This image is a VI Snippet, an executable image of LabVIEW code. The LabVIEW version is shown on the top-right hand corner. You can download it, then drag-and-drop it onto the LabVIEW block diagram from a file browser, and it will appear as runnable, editable code.

Liberty BASIC

<lang lb>input$ ="abcdefgABCDEFG012345" print input$ print ReversedStr$( input$)

end

function ReversedStr$(in$)

   for i =len(in$) to 1 step -1
   ReversedStr$ =ReversedStr$ +mid$( in$, i, 1)
   next i

end function</lang>

Logo

REVERSE works on both words and lists. <lang logo>print reverse "cat ; tac</lang>

Lua

Built-in string.reverse(s) or s:reverse(). <lang lua>theString = theString:reverse()</lang>

M4

<lang m4>define(`invert',`ifelse(len(`$1'),0,,`invert(substr(`$1',1))'`'substr(`$1',0,1))')</lang>

Mathematica

<lang mathematica>StringReverse["asdf"]</lang>

MATLAB

A built-in function, "fliplr(string)" handles reversing a string of ASCII characters. Unicode is a whole other beast, if you need this functionality test to see if "fliplr()" properly handles the unicode characters you use. If it doesn't then you will need to code a function that is specific to your application.

Sample Usage: <lang MATLAB>>> fliplr(['She told me that she spoke English and I said great. '... 'Grabbed her hand out the club and I said lets skate.'])

ans =

.etaks s'tel dias I dna bulc eht tuo dnah reh debbarG .taerg dias I dna hsilgnE ekops ehs taht em dlot ehS </lang>

MAXScript

<lang maxscript>fn reverseString s = (

   local reversed = ""
   for i in s.count to 1 by -1 do reversed += s[i]
   reversed

)</lang>

Mirah

<lang mirah>def reverse(s:string)

   StringBuilder.new(s).reverse

end

puts reverse('reversed')</lang>

Modula-3

<lang modula3>MODULE Reverse EXPORTS Main;

IMPORT IO, Text;

PROCEDURE String(item: TEXT): TEXT =

 VAR result: TEXT := "";
 BEGIN
   FOR i := Text.Length(item) - 1 TO 0 BY - 1 DO
     result := Text.Cat(result, Text.FromChar(Text.GetChar(item, i)));
   END;
   RETURN result;
 END String;

BEGIN

 IO.Put(String("Foobarbaz") & "\n");

END Reverse.</lang> Output:

zabrabooF

MUMPS

<lang MUMPS> REVERSE

;Take in a string and reverse it using the built in function $REVERSE
NEW S
READ:30 "Enter a string: ",S
WRITE !,$REVERSE(S)
QUIT

</lang>

Example:

USER>D REVERSE^ROSETTA
Enter a string: Hello, World!
!dlroW ,olleH

Nemerle

Supporting Combining Characters

Compile with:

ncc -reference:System.Windows.Forms reverse.n

<lang Nemerle>using System; using System.Globalization; using System.Windows.Forms; using System.Console; using Nemerle.Utility.NString;

module StrReverse {

   UReverse(text : string) : string
   {
       mutable output = [];
       def elements = StringInfo.GetTextElementEnumerator(text);
       while (elements.MoveNext())
           output ::= elements.GetTextElement().ToString();
       Concat("", output.Reverse());
   }
   
   Main() : void
   {
       def test = "as⃝df̅";
       MessageBox.Show($"$test --> $(UReverse(test))");  //for whatever reason my console didn't display Unicode properly, but a MessageBox worked
   }

}</lang>

Basic Reverse

Doesn't require the System.Globalization namespace, probably a little less overhead. <lang Nemerle>Reverse(text : string) : string {

   mutable output = [];
   foreach (c in text.ToCharArray())
       output ::= c.ToString();
   Concat("", output)

}</lang>

NetRexx

<lang NetRexx>/* NetRexx */

options replace format comments java crossref savelog symbols nobinary

reverseThis = 'asdf' sihTesrever = reverseThis.reverse

say reverseThis say sihTesrever

return </lang>

Output

asdf
fdsa

Nial

<lang nial>reverse 'asdf' =fdsa</lang>

NewLISP

<lang NewLISP>(reverse "!dlroW olleH")</lang>

Objeck

<lang objeck> result := "asdf"->Reverse(); </lang>

Objective-C

This extends the NSString object adding a reverseString class method.

<lang objc>#import <Foundation/Foundation.h>

@interface NSString (Extended) -(NSString *)reverseString; @end

@implementation NSString (Extended) -(NSString *) reverseString {

   NSUInteger len = [self length];
   NSMutableString *rtr=[NSMutableString stringWithCapacity:len];
   //        unichar buf[1];
   
   while (len > (NSUInteger)0) { 
       unichar uch = [self characterAtIndex:--len]; 
       [rtr appendString:[NSString stringWithCharacters:&uch length:1]];
   }
   return rtr;

} @end</lang>

Usage example:

<lang objc>int main() {

   NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
       
   NSString *test = [@"!A string to be reverted!" reverseString];
   
   NSLog(@"%@", test);
   
   [pool release];
   return 0;

}</lang>

Supporting combining characters

Extra credit

<lang objc>#import <Foundation/Foundation.h>

@interface NSString (Extended) -(NSString *)reverseString; @end

@implementation NSString (Extended) -(NSString *)reverseString { NSInteger l = [self length] - 1; NSMutableString *ostr = [NSMutableString stringWithCapacity:[self length]]; while (l >= 0) { NSRange range = [self rangeOfComposedCharacterSequenceAtIndex:l]; [ostr appendString:[self substringWithRange:range]]; l -= range.length; } return ostr; } @end</lang>

Usage example:

<lang objc>int main() {

   NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
       
   NSString *test = [@"as⃝df̅" reverseString];
   
   NSLog(@"%@", test);
   
   [pool release];
   return 0;

}</lang>

OCaml

Here a version that returns a new allocated string (preserving the original one):

<lang ocaml>let rev_string str =

 let len = String.length str in
 let res = String.create len in
 let last = len - 1 in
 for i = 0 to last do
   let j = last - i in
   res.[i] <- str.[j];
 done;
 (res)</lang>

and here with in place modification:

<lang ocaml>let rev_string str =

 let last = String.length str - 1 in
 for i = 0 to last / 2 do
   let j = last - i in
   let c = str.[i] in
   str.[i] <- str.[j];
   str.[j] <- c;
 done</lang>

here is a 100% functionnal string reversing function:

<lang ocaml>let rec revs strin list index =

 if List.length list = String.length strin
 then String.concat "" list
 else revs strin ((String.sub strin index 1)::list) (index+1)</lang>

revs "Hello World!" [] 0 will return "!dlroW olleH"

Octave

<lang octave>s = "a string"; rev = s(length(s):-1:1)</lang>

OpenEdge/Progress

<lang Progress (OpenEdge ABL)>FUNCTION reverseString RETURNS CHARACTER (

  INPUT i_c AS CHARACTER

):

  DEFINE VARIABLE cresult AS CHARACTER   NO-UNDO.
  DEFINE VARIABLE ii      AS INTEGER     NO-UNDO.

  DO ii = LENGTH( i_c ) TO 1 BY -1:
     cresult = cresult + SUBSTRING( i_c, ii, 1 ).
  END.
  RETURN cresult.

END FUNCTION.

MESSAGE reverseString( "asdf" ) VIEW-AS ALERT-BOX. </lang>

Oz

Strings are lists. A function "Reverse" defined on lists is part of the implementation. <lang oz>{System.showInfo {Reverse "!dlroW olleH"}}</lang>

An efficient (tail-recursive) implementation could look like this: <lang oz>local

  fun {DoReverse Xs Ys}
     case Xs of nil then Ys
     [] X|Xr then {DoReverse Xr X|Ys}
     end
  end

in

  fun {Reverse Xs} {DoReverse Xs nil} end

end</lang>

Oz uses a single-byte encoding by default. If you decide to use a multi-byte encoding, Reverse will not work correctly.

PARI/GP

<lang parigp> reverse(expr)=my(v=Vec(Str(expr)),n=length(v));concat(vector(n,i,v[n-i+1])); </lang>

Pascal

The following examples handle correctly only single-byte encodings.

Standard Pascal

The following only works on implementations which implement Level 1 of standard Pascal (many popular compilers don't).

Standard Pascal doesn't have a separate string type, but uses arrays of char for strings. Note that Standard Pascal doesn't allow a return type of char array, therefore the destination array is passed through a var parameter (which is more efficient anyway). <lang pascal>{ the result array must be at least as large as the original array } procedure reverse(s: array[min .. max: integer] of char, var result: array[min1 .. max1: integer] of char);

var
 i, len: integer;
begin
 len := max-min+1;
 for i := 0 to len-1 do
  result[min1 + len-1 - i] := s[min + i]
end;</lang>

<lang pascal> {Copy and paste it in your program} function revstr(my_s:string):string;

   var out_s:string;
   ls,i:integer;
   begin
   ls:=length(my_s);
   for i:=1 to ls do
   out_s:=out_s+my_s[ls-i+1];
   revstr:=out_s;
   end;

</lang>

Extended Pascal, Turbo Pascal, Delphi and compatible compilers

<lang pascal>function reverse(s:string):string; var i:integer; var tmp:char; begin

   for i:=1 to length(s) div 2 do
     begin
      tmp:=s[i];
      s[i]:=s[length(s)+1-i];
      s[length(s)+1-i]:=tmp;
      reverse:=s;
     end;

end;</lang>

Perl

This reverses characters (code points):

<lang perl>$string = "visor"; $flip = reverse $string; # becomes "rosiv"</lang>

This reverses graphemes: <lang perl>$string = "Jose\x{301}"; # "José" in NFD $flip = join("", reverse $string =~ /\X/g); # becomes "ésoJ"</lang>

Perl 6

<lang perl6># Not transformative. my $reverse = flip $string;

or

say "hello world".flip;</lang> Perl 6 is specced to work on graphemes by default, but current implementations are limited to processing codepoints.

PHP

<lang php>strrev($string);</lang>

If you want Unicode support, you have to use some multibyte function. Sadly, PHP doesn't contain mb_strrev(). One of functions which support Unicode and is useful in this case is preg_split().

<lang php>// Will split every Unicode character to array, reverse array and will convert it to string. join(, array_reverse(preg_split('""u', $string, -1, PREG_SPLIT_NO_EMPTY)));</lang>

PicoLisp

<lang PicoLisp>(pack (flip (chop "äöüÄÖÜß")))</lang> Output:

-> "ßÜÖÄüöä"

PL/I

<lang PL/I> s = reverse(s); </lang>

Pop11

<lang pop11>define reverse_string(s);

   lvars i, l = length(s);
   for i from l by -1 to 1 do
       s(i);
   endfor;
   consstring(l);

enddefine;</lang>

PostScript

The following implementation works on arrays of numerics as well as characters ( string ).

<lang PostScript> /reverse{ /str exch def /temp str 0 get def /i 0 def str length 2 idiv{ /temp str i get def str i str str length i sub 1 sub get put str str length i sub 1 sub temp put /i i 1 add def }repeat str pstack }def </lang> Output is as below: <lang PostScript> [1 2 3] reverse % input [3 2 1]

(Hello World) reverse % input (dlroW olleH) </lang>

PowerShell

Test string <lang powershell>$s = "asdf"</lang>

Array indexing

Creating a character array from the end to the string's start and join it together into a string again.

Works with: PowerShell version 1

<lang powershell>[string]::Join(, $s[$s.Length..0])</lang>

Works with: PowerShell version 2

<lang powershell>-join ($s[$s.Length..0])</lang>

Works with: PowerShell version 2

<lang powershell>[array]::Reverse($s)</lang>

Regular expressions

Creating a regular expression substitution which captures every character of the string in a capture group and uses a reverse-ordered string of references to those to construct the reversed string.

Works with: PowerShell version 1

<lang powershell>$s -replace

     ('(.)' * $s.Length),
     [string]::Join(, ($s.Length..1 | ForEach-Object { "`$$_" }))</lang>

Works with: PowerShell version 2

<lang powershell>$s -replace

     ('(.)' * $s.Length),
     -join ($s.Length..1 | ForEach-Object { "`$$_" } )</lang>

Prolog

Works with SWI-Prolog.

<lang prolog>reverse("abcd", L), string_to_list(S,L).</lang> <lang hml>output : L = [100,99,98,97], S = "dcba". </lang>

The main workings are hidden inside the reverse/2 predicate, so lets write one to see how it works: <lang prolog>accRev([H|T], A, R) :- accRev(T, [H|A], R). accRev([], A, A).

rev(L,R) :- accRev(L,[],R).</lang>

Protium

Padded out, variable length Chinese dialect <lang html><# 显示指定变量反转顺序字串>集装箱|猫坐在垫子</#></lang>

This assigns the reverse of 'the cat sat on the mat' to the variable 'container' and displays the result which is

子垫在坐猫

which Google Translate renders as

Sub-pad sitting cat

.

The same again but with everything in Korean. <lang html><# 보이십 할당하 변물건 열거꾸 문자그>컨테이너|고양이가 매트 위에 앉아</#></lang>

Reversing the Korean makes an untranslatable-by-Google mess of the sentence, viz

아앉 에위 트매 가이양고

.

The short-opcode version in English dialect is <lang html><@ SAYLETVARREVLIT>集装箱|猫坐在垫子</@></lang>

Protium works in Unicode.

PureBasic

<lang PureBasic>Debug ReverseString("!dekrow tI")</lang>

Python

Optimized for user input

<lang python>raw_input()[::-1]</lang>

Already known string

<lang python>string[::-1]</lang>

Unicode reversal

(See this article for more information)

 Reverse a Unicode string with proper handling of combining characters

import unicodedata

def ureverse(ustring):

   
   Reverse a string including unicode combining characters

   Example:
       >>> ucode = .join( chr(int(n, 16))
                            for n in ['61', '73', '20dd', '64', '66', '305'] )
       >>> ucoderev = ureverse(ucode)
       >>> ['%x' % ord(char) for char in ucoderev]
       ['66', '305', '64', '73', '20dd', '61']
       >>> 
   
   groupedchars = []
   uchar = list(ustring)
   while uchar:
       if 'COMBINING' in unicodedata.name(uchar[0], ):
           groupedchars[-1] += uchar.pop(0)
       else:
           groupedchars.append(uchar.pop(0))
   # Grouped reversal
   groupedchars = groupedchars[::-1]

   return .join(groupedchars)

if __name__ == '__main__':

   ucode = .join( chr(int(n, 16))
                    for n in ['61', '73', '20dd', '64', '66', '305'] )
   ucoderev = ureverse(ucode)
   print (ucode)
   print (ucoderev)</lang>

Qi

It's simplest just to use the common lisp REVERSE function. <lang Qi>(REVERSE "ABCD")</lang>

R

Works with: R version 2.8.1

The following code works with UTF-8 encoded strings too. <lang R>revstring <- function(stringtorev) {

  return(
     paste(
          strsplit(stringtorev,"")1[nchar(stringtorev):1]
          ,collapse="")
          )

} revstring("asdf") revstring("m\u00f8\u00f8se") Encoding("m\u00f8\u00f8se") # just to check if on your system it's something

                             # different!</lang>

Outputs

[1] "fdsa"
[1] "esøøm"
[1] "UTF-8"

R can encode strings in Latin1 and UTF-8 (the default may depend on the locale); the Encoding(string) can be used to know if the string is encoded in Latin1 or UTF-8; the encoding can be forced (Encoding(x) <- "latin1"), or we can use iconv to properly translate between encodings whenever possible.

REBOL

<lang REBOL>print reverse "asdf"</lang>

Note the string is reversed in place. If you were using it anywhere else, you would find it reversed:

<lang REBOL>x: "asdf" print reverse x print x ; Now reversed.</lang>

REBOL/View 2.7.6.3.1 14-Mar-2008 does not handle Unicode strings. This is planned for REBOL 3.

Retro

<lang Retro> with strings' "asdf" reverse puts </lang>

REXX

<lang rexx> p='A man, a plan, a canal, Panama!' q=reverse(p) say p say q </lang> Output:

A man, a plan, a canal, Panama!
!amanaP ,lanac a ,nalp a ,nam A

RLaB

<lang RLaB> >> x = "rosettacode" rosettacode

// script rx = ""; for (i in strlen(x):1:-1) {

 rx = rx + substr(x, i);

}

>> rx edocattesor

</lang>

Ruby

<lang ruby>str = "asdf" reversed = str.reverse</lang> or <lang ruby>"asdf".reverse</lang>

SAS

<lang sas>data _null_; length a b $11; a="I am Legend"; b=reverse(a); put a; put b; run;</lang>

Sather

<lang sather>class MAIN is

 main is
   s ::= "asdf";
   reversed ::= s.reverse; 
   -- current implementation does not handle multibyte encodings correctly
 end;

end;</lang>

Scala

Easy way:

<lang scala>"asdf".reverse</lang>

Unicode-aware. I can't guarantee it get all the cases, but it does work with combining characters as well as supplementary characters. I did not bother to preserve the order of newline characters, and I didn't even consider directionality beyond just ruling it out.

<lang scala>def reverseString(s: String) = {

 import java.lang.Character._
 
 val combiningTypes = List(NON_SPACING_MARK, ENCLOSING_MARK, COMBINING_SPACING_MARK)
 def isCombiningCharacter(c: Char) = combiningTypes contains c.getType
 def isCombiningSurrogate(high: Char, low: Char) = combiningTypes contains getType(toCodePoint(high, low))
 def isCombining(l: List[Char]) = l match {
   case List(a, b) => isCombiningSurrogate(a, b)
   case List(a) => isCombiningCharacter(a)
   case Nil => true
   case _ => throw new IllegalArgumentException("isCombining expects a list of up to two characters")
 }
 
 def cleanSurrogate(l: List[Char]) = l match {
   case List(a, b) if a.isHighSurrogate && b.isLowSurrogate => l
   case List(a, b) if a.isLowSurrogate => Nil
   case List(a, b) => List(a)
   case _ => throw new IllegalArgumentException("cleanSurrogate expects lists of two characters, exactly")
 }
 
 def splitString(string: String) = (string+" ").iterator sliding 2 map (_.toList) map cleanSurrogate toList

 def recurse(fwd: List[List[Char]], rev: List[Char]): String = fwd match {
   case Nil => rev.mkString
   case c :: rest =>
     val (combining, remaining) = rest span isCombining
     recurse(remaining, c ::: combining.foldLeft(List[Char]())(_ ::: _) ::: rev)
 }
 recurse(splitString(s), Nil)

}</lang>

REPL on Windows doesn't handle Unicode, so I'll show the bytes instead:

scala> res71 map ("\\u%04x" format _.toInt)
res80: scala.collection.immutable.IndexedSeq[String] = IndexedSeq(\u0061, \u0073, \u20dd, \u0064, \u0066, \u0305)

scala> reverseString(res71) map ("\\u%04x" format _.toInt)
res81: scala.collection.immutable.IndexedSeq[String] = IndexedSeq(\u0066, \u0305, \u0064, \u0073, \u20dd, \u0061)

Scheme

<lang scheme>(define (string-reverse s)

 (list->string (reverse (string->list s))))</lang>

> (string-reverse "asdf")
"fdsa"

Sed

<lang sed>#!/bin/sed -f

/../! b

Reverse a line. Begin embedding the line between two newlines

s/^.*$/\ &\ /

Move first character at the end. The regexp matches until
there are zero or one characters between the markers

tx

x

s/$\n.$$.*$$.\n$/\3\2\1/ tx

Remove the newline markers

s/\n//g

</lang>

Seed7

Seed7 strings are encoded with UTF-32 therefore no special Unicode solution is necessary

<lang seed7>$ include "seed7_05.s7i";

const func string: reverse (in string: stri) is func

 result
   var string: result is "";
 local
   var integer: index is 0;
 begin
   for index range length(stri) downto 1 do
     result &:= stri[index];
   end for;
 end func;

const proc: main is func

 begin
   writeln(reverse("Was it a cat I saw"));
 end func;</lang>

Output:

was I tac a ti saW

Slate

In-place reversal: <lang slate>'asdf' reverse</lang> Non-destructive reversal: <lang slate>'asdf' reversed</lang>

Smalltalk

<lang smalltalk>'asdf' reverse</lang>

SNOBOL4

ASCII-only <lang snobol> output = reverse(reverse("reverse")) end</lang>

output: <lang>reverse</lang>

Standard ML

<lang sml>val str_reverse = implode o rev o explode; val string = "asdf"; val reversed = str_reverse string;</lang>

Tcl

<lang tcl>package require Tcl 8.5 string reverse asdf</lang>

TI-83 BASIC

The following program will place the reverse of Str1 in Str0. Note: length( and sub( can be found in the catalog. <lang ti83b>:"ASDF"→Str1

" "→Str0

length(Str1)→B

For(A,B,1,-1)

Str0+sub(Str1,A,1)→Str0

End

sub(Str0,2,B)→Str0</lang>

The reason a single space must be placed in Str0 and then later removed is that for some reason, the TI-83 will not allow concatenation with an empty string (so Str0+sub... would fail).

TUSCRIPT

<lang tuscript> $$ MODE TUSCRIPT SET input="was it really a big fat cat i saw" SET reversetext=TURN (input) PRINT "before: ",input PRINT "after: ",reversetext </lang> Output:

before: was it really a big fat cat i saw
after:  was i tac taf gib a yllaer ti saw

Unlambda

Reverse the whole input: <lang Unlambda>``@c`d``s`|k`@c</lang>

Ursala

<lang Ursala>#import std

cast %s

example = ~&x 'asdf'

verbose_example = reverse 'asdf'</lang> output:

'fdsa'

VBA

Visual Basic for Applications.

Non-recursive version

<lang VBA> Public Function Reverse(aString as String) as String ' returns the reversed string dim L as integer 'length of string dim newString as string

newString = "" L = len(aString) for i = L to 1 step -1

newString = newString & mid$(aString, i, 1)

next Reverse = newString End Function </lang>

Recursive version

<lang VBA> Public Function RReverse(aString As String) As String 'returns the reversed string 'do it recursively: cut the string in two, reverse these fragments and put them back together in reverse order Dim L As Integer 'length of string Dim M As Integer 'cut point

L = Len(aString) If L <= 1 Then 'no need to reverse

 RReverse = aString

Else

 M = Int(L / 2)
 RReverse = RReverse(Right$(aString, L - M)) & RReverse(Left$(aString, M))

End If End Function </lang>

Example dialogue

print Reverse("Public Function Reverse(aString As String) As String")
gnirtS sA )gnirtS sA gnirtSa(esreveR noitcnuF cilbuP

print RReverse("Sunday Monday Tuesday Wednesday Thursday Friday Saturday Love")
evoL yadrutaS yadirF yadsruhT yadsendeW yadseuT yadnoM yadnuS

print RReverse(Reverse("I know what you did last summer"))
I know what you did last summer

Vedit macro language

This routine reads the text from current line, reverses it and stores the reversed string in text register 10:

<lang vedit>Reg_Empty(10) for (BOL; !At_EOL; Char) {

   Reg_Copy_Block(10, CP, CP+1, INSERT)

}</lang>

This routine reverses the current line in-place:

<lang vedit>BOL while (!At_EOL) {

   Block_Copy(EOL_pos-1, EOL_pos, DELETE)

}</lang>

Yorick

This only handles ASCII characters. It works by converting a string to an array of char; dropping the last character (which is the null byte); reversing the order of the characters; then converting back to a string. <lang yorick>strchar(strchar("asdf")(:-1)(::-1))</lang>

Visual Basic .NET

<lang vbnet> Function Reverse(ByVal s As String) As String

   Dim t() as Char = s.toCharArray
   Array.reverse(t)
   Return new String(t)
 End Function</lang>