Extract the final path component

Challenge

Your job

int basename_of(const char *path, char *out, size_t cap);

Copy the part of path after the last / into out (NUL-terminated). A path with no / is its own basename. Return bytes written, or -1 on NULL/overflow.

Examples

• "/a/b/file.txt" → "file.txt"
• "plain.c" → "plain.c"

Hints

1. Find the last / with a reverse scan (or strrchr).
2. Copy everything after it.

Why this matters

Pulling the filename out of a path is a constant chore — and doing it by hand avoids the surprising in-place behaviour of libc basename().

Starter code

#include <stddef.h>
int basename_of(const char *path, char *out, size_t cap) {
    /* TODO */
    (void)path; (void)out; (void)cap;
    return -1;
}

Common mistakes

Including the slash. Mishandling a trailing slash. No overflow guard.

Edge cases to handle

No slash. Trailing slash → empty string. Tiny buffer.

Complexity

O(path length).

Background lessons

• fopen and the stdio model
• Parsing CSV

Up next

• Read a fixed-size record