gistfile1.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

typedef struct
  { unsigned long length
  ; char *data
  ;
  } String;

String* String_shell ()
  { return malloc (sizeof (long) + sizeof (char*))
  ;
  }

String* String_new (unsigned long length)
  { String* out = String_shell ()
  ; out->data   = malloc (sizeof (char) * length)
  ; out->length = 0
  ; return out
  ;
  }

void String_reverse (String* source, String* dest)
  { unsigned long len = dest->length = source->length
  ; unsigned long i
  ; for ( i = 0
        ; i < len
        ; i++
        )
        dest->data [i] = source->data [len - i - 1]
  ;
  }

void String_print (String* str)
  { fwrite (str->data, str->length, 1, stdout)
  ;
  }

int main (int argc, char** argv)
  { if (argc > 1)
       { unsigned long len = strlen (argv[1])
       ; String*       in  = String_new (len)
       ; String*       out = String_new (len)
       ; in->length        = len
       ; in->data          = argv[1]
       ; String_reverse      (in, out)
       ; String_print        (out)
       ; fputs               ("\n", stdout)
       ; return              0
       ;
       }
    else
       { fputs  ("Not enough arguments.\n", stderr)
       ; return 1
       ;
       }
  }