c - Quick strlen question

Question

I've come to bother you all with another probably really simple C question.

Using the following code:

int get_len(char *string){

    printf("len: %lu
", strlen(string));

    return 0;
}

int main(){

    char *x = "test";
    char y[4] = {'t','e','s','t'};

    get_len(x); // len: 4
    get_len(y); // len: 6

    return 0;
}

2 questions. Why are they different and why is y 6? Thanks guys.

EDIT: Sorry, I know what would fix it, I kind of just wanted to understand what was going on. So does strlen just keep forwarding the point till it happens to find a ? Also when I did strlen in the main function instead of in the get_len function both were 4. Was that just a coincidence?

Answer 1

y is not null-terminated. strlen() counts characters until it hits a null character. Yours happened to find one after 6, but it could be any number. Try this:

char y[] = {'t','e','s','t', ''};

Here's what an implementation of strlen() might look like (off the top of my head -- don't have my K&R book handy, but I believe there's an implementation given there):

size_t strlen(const char* s)
{
    size_t result = 0;
    while (*s++) ++result;
    return result;
}