mkdir -p implemented in C

mkdir_p.c

#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>   /* mkdir(2) */
#include <errno.h>

/* Make a directory; already existing dir okay */
static int maybe_mkdir(const char* path, mode_t mode)
{
    struct stat st;
    errno = 0;

    /* Try to make the directory */
    if (mkdir(path, mode) == 0)
        return 0;

    /* If it fails for any reason but EEXIST, fail */
    if (errno != EEXIST)
        return -1;

    /* Check if the existing path is a directory */
    if (stat(path, &st) != 0)
        return -1;

    /* If not, fail with ENOTDIR */
    if (!S_ISDIR(st.st_mode)) {
        errno = ENOTDIR;
        return -1;
    }

    errno = 0;
    return 0;
}

int mkdir_p(const char *path)
{
    /* Adapted from http://stackoverflow.com/a/2336245/119527 */
    char *_path = NULL;
    char *p; 
    int result = -1;
    mode_t mode = 0777;

    errno = 0;

    /* Copy string so it's mutable */
    _path = strdup(path);
    if (_path == NULL)
        goto out;

    /* Iterate the string */
    for (p = _path + 1; *p; p++) {
        if (*p == '/') {
            /* Temporarily truncate */
            *p = '\0';

            if (maybe_mkdir(_path, mode) != 0)
                goto out;

            *p = '/';
        }
    }   

    if (maybe_mkdir(_path, mode) != 0)
        goto out;

    result = 0;

out:
    free(_path);
    return result;
}

mkdir_p.h

#ifndef MKDIR_P_H
#define MKDIR_P_H

int mkdir_p(const char *path);

#endif /* MKDIR_P_H */

SConstruct

env = Environment(
    CCFLAGS = ['-Wall', '-Werror'],
)
env.Program('mkdir_p_test', ['mkdir_p.c', 'test.c'])

test.c

#include <stdio.h>
#include "mkdir_p.h"

int main(int argc, char **argv)
{
    const char *path;
    int rc;

    if (argc < 2) {
        fprintf(stderr, "Missing argument: path\n");
        return 1;
    }

    path = argv[1];

    rc = mkdir_p(path);

    fprintf(stderr, "mkdir_p(\"%s\") returned %d: %m\n", path, rc);

    return (rc == 0) ? 0 : 2;
}

BTW mkdir_p( "" ) accesses beyond allocated memory since it assumes the path length is non-zero. Seems it should return ENOENT in this case, as mkdir does for an empty string.

As for optimization, would it make sense to just try maybe_mkdir in the beginning, for the probably-common case where the parent directories already exist?

Thanks for the useful functions and careful implementation.

This doesn't make sense:

if (_path == NULL)
        goto out;

Because it executes free(_path); which is undefined for NULL.

@SamuelMarks

This doesn't make sense:

if (_path == NULL)
        goto out;

Because it executes free(_path); which is undefined for NULL.

Incorrect. From free(3p):

If ptr is a null pointer, no action shall occur.

https://stackoverflow.com/a/2360462 oh looks like my best-practices is a bit out-of-date…