Why this code gives me segfault when the substring is not found?

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I wrote this function based on strstr.
If the substring is found, it returns it. But when it's not found, gives me segfault. What should I change?

char	*ft_strstr(char *str, char *to_find)
{
	int	i;
	int	j;

	i = 0;
	j = 0;
	if (to_find[j] == '\0')
		return (str);
	while (str[i] != '\0')
	{
		while (str[i + j] == to_find[j] && str[i + j] != '\0')
			j++;
		if (to_find[j] == '\0')
			return (str + i);
		i++;
		j = 0;
	}
	return (0);
}

What I have tried:

I've changed it many times, but no luck.

Posted 7-Feb-23 21:32pm

Navid Rigi Ebrahimi

Updated 7-Feb-23 21:53pm

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Comments

Andre Oosthuizen 8-Feb-23 4:06am

Search for string inside another string might help - https://www.codingame.com/playgrounds/14213/how-to-play-with-strings-in-c/search-within-a-string#:~:text=The%20function%20strstr%20returns%20the,a%20substring%20of%20another%20string.

Navid Rigi Ebrahimi 8-Feb-23 4:20am

great, thanks

1 solution

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This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

OriginalGriff · Accepted Answer · 2023-02-07T21:53:00

Look at your code: you have a loop limited to the length of the string, but you access characters beyond that limit:

while (str[i] != '\0')
{
    while (str[i + j] == to_find[j] && str[i + j] != '\0')

Since you increment j without checking if to_find is exhausted, you can go well outside the loop bounds.

Use the debugger to follow exactly what your code is doing while it is running, and you'll see where your problem happens and what your variables contain.

Why this code gives me segfault when the substring is not found?

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Why this code gives me segfault when the substring is not found?

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