What am I doing wrong to get segmentation fault?-CodePudding

I'm trying to replicate the function strstr. When my function finds to_find in str it works accordingly. If to_find is not in str I get segmentation fault, even though I created a condition to return NULL; if my str gets to '\o' without getting any matches.

This is my code:

#include <stdio.h>

char    *ft_strstr(char *str, char *to_find)
{
    char    *to_find_copy;
    char    *str_copy;

    to_find_copy = to_find;
    str_copy = str;
    while (*to_find_copy != '\0' || *str_copy != '\0')
    {
        if (*to_find_copy == *str_copy)
        {
            to_find_copy  ;
            str_copy  ;
        }
        else
        {
            to_find_copy = to_find;
            str  ;
            str_copy  ;
        }
    }
    if (*str_copy == '\0')
        return NULL;
    return (str);
}


int main(void)
{
    char str[50] = "Yesterday I went to the store";
    char to_find[50] = "Z";
    char *ptr;

    printf("\nString 1:   %s\nString 2:   %s\n", str, to_find);

    ptr = ft_strstr(str, to_find);
    
    printf("\nEncontrou:    %s\n", ptr);

    return 0;
}

Output:

String 1:   Yesterday I went to the store 
String 2:   Zer
zsh: segmentation fault  ./a.out

It should return NULL. I believe I must be overwriting the memory of an array but I don't understand why.

PS. I can only use 25 line in the function at max.

CodePudding user response：

You could try this code. Your code didn't give segmentation fault on my system, but it doesn't give correct results. It always returns NULL

I will return String "NULL" instead of NULL...

#include <stdio.h>

char *ft_strstr(char *str, char *to_find) {

  int found = 0;
  char *return_value = str;

  while (found == 0) {
    if (*to_find == *str) {
      to_find  ;
      str  ;
    } else {
      str  ;
      return_value  ;
    }
    if (*to_find == '\0') {
      found = 1;
      return return_value;
    }

    if (*str == '\0') {
      return "NULL";
    }
  }
}


int main(void) {
  char str[50] = "Yesterday I went to the store";
  char to_find[50] = "Zer";
  char to_find_2[50] = "ent";
  char *ptr;

  printf("\nString 1:   %s\nString 2:   %s\n", str, to_find);
  ptr = ft_strstr(str, to_find);
  printf("\nFound:    %s\n\n", ptr);
  printf("\nString 1:   %s\nString 2:   %s\n", str, to_find_2);
  ptr = ft_strstr(str, to_find_2);
  printf("\nFound:    %s\n", ptr);
  return 0;
}

OUTPUT:

> ./strstr

String 1:   Yesterday I went to the store
String 2:   Zer

Found:    NULL


String 1:   Yesterday I went to the store
String 2:   ent

Found:    ent to the store