(Weird result so far...) Rewind a C string from the last pointer to the first pointer which the start of the string.

rewind_string.c

char *rewind_string(char *last_char) {
    // Prevent NUL byte.
    if (*last_char == '\0' || last_char == NULL) {
        return NULL;
    }
    
    char *first_char;
    
    // Rewind to the pointer pointing to first character.
    for (first_char = last_char; *first_char != '\0'; first_char--);
    return (*first_char == '\0') ? (first_char + 1) : first_char;
}

I would like to rewind a string pointer from pointing to last character to first character. But, the result is a little wired because extra characters were found in front of the string.

It seems that precise rewinding has to use the string length to prevent undesired characters being found.