Memory Leak - Valgrind - "0 bytes lost in 59 blocks"

Question

Valgrind says that I have a memory leak of 59 bytes in 59 blocks because of my function ft_strdup :

char            *ft_strdup(const char *s)
{
    char    *dup;
    int     i;

    i = 0;
    dup = (char *)malloc((ft_strlen(s) + 1) * sizeof(char));
    if (!dup)
        return (NULL);
    while (s[i])
    {
        dup[i] = s[i];
        i++;
    }
    dup[i] = '\0';
    return (dup);
}

But when I change the size of the allocation to :

dup = (char *)malloc(ft_strlen(s) * sizeof(char));

Valgrind shows me this result :

==36929==    definitely lost: 0 bytes in 59 blocks
==36929==    indirectly lost: 0 bytes in 0 blocks

Why the 59 blocks still shows up instead of 0 blocks since there isn't any bytes lost?

Answer 1

When you change the size of the allocation to:

dup = (char *)malloc(ft_strlen(s) * sizeof(char));

you're overwriting the memory you haven't allocated with a termination \0 character, which is pretty much the source of your problem.

Agree, valgrind could have given the better diagnostic, but it could have given the worse as well.