malloc segfault

#include <stdlib.h>

int     ft_strlen(char *str)
{
    int l;

    l = 0;
    while (*str++ != '\0')
        l++;
    return (l);
}

char    *ft_strdup(char *src)
{
    int     run;
    char    *str;

    run = ft_strlen(src);
    if (run == 0)
        return (0);
    str = (char*)malloc(sizeof(char) * (run + 1));
    run = 0;
    while (src[run] != '\0')
    {
        str[run] = src[run];
        run++;
    }
    str[run] = '\0';
    return (str);
}


#include <stdio.h>

char    *ft_strdup(char *src);

int main()
    {
              char *f = "";
               printf("%s\n", f);
                printf("%s\n", ft_strdup(f));
            }