Thread: C strings pointer manipulation problem

i have been trying resolve no1 of ruby quiz problems - http://www.rubyquiz.com/quiz1.html in c, program keeps complaining me when try free pointer. please, can me find error? here's code far:

code:

#include <string.h>  #include <stdio.h>  #include <ctype.h>  #include <stdlib.h>    #define group_length 5 // words in groups of 5 characters    char *to_alpha(char *msg);    int main(void)  {      char msg[] = "bla bla";      printf("%s\n", to_alpha(msg));      return exit_success;  }    int exit_error(char * error)  {      perror(error);      return exit_failure;  }    /*   * uppercases message, removes non-alpha chars.   * adds x end of message.   */  char *to_alpha(char *msg)  {      int len_duplicate;       char *duplicate;      if ((duplicate = malloc(strlen(msg) + 1)) == null)          exit_error("null duplicate string");        // pass throught strings once, copy , uppercase      // letters [a-za-z]      (len_duplicate = 0; *msg; *msg++)          if (isalpha(*msg))          {                 *duplicate++ = toupper(*msg);              len_duplicate++;          }           // append 'x' letters rest of string      // until divides group_length in clean manner:      if (len_duplicate % group_length != 0)          while (len_duplicate % group_length != 0)          {              *duplicate++ = 'x';              len_duplicate++;          }      *duplicate++ = '0';        strcpy(msg, duplicate);      free(duplicate);      return msg;  }

the address you're passing free() isn't address got malloc().

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