2

Reverse the contents of a string of characters

  1. #include <stdio.h>
  2. #include <string.h>
  3.  
  4. char *reverse( char *s ) {
  5.     char *p, *q;
  6.  
  7.     for ( p = s, q = s+strlen(s)-1; q > p; p++, q-- ) {
  8.         char c = *p;
  9.         *p = *q;
  10.         *q = c;
  11.     }
  12.     return s;
  13. }
  14.  
  15. void test( char *s )
  16. {
  17.     /* printing s and reverse( s ) in one statement calls reverse first! */
  18.     printf( "[%s]", s );
  19.     printf( "<->" );
  20.     printf( "[%s]", reverse( s ));
  21.     printf( "\n" );
  22. }
  23.  
  24. main( ) {
  25.     /* don't use char * (read-only) with cl /GF */
  26.     char s1[] = "123";
  27.     char s2[] = "12";
  28.     char s3[] = "";
  29.     char *s4 = "abcdef";
  30.  
  31.     test( s1 );
  32.     test( s2 );
  33.     test( s3 );
  34.     test( s4 ); /* segmentation fault */
  35. }
$ gcc -o reverse reverse.c
$ ./reverse
[123]<->[321]
[12]<->[21]
[]<->[]
Segmentation fault

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