在 C 中创建一个新目录

Question

I want to write a program that checks for the existence of a directory; if that directory does not exist then it creates the directory and a log file inside of it, but if the directory already exists, then it just creates a new log file in that folder.

How would I do this in C with Linux?

Answer 1

Look at stat for checking if the directory exists,

And mkdir , to create a directory.

#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

struct stat st = {0};

if (stat("/some/directory", &st) == -1) {
    mkdir("/some/directory", 0700);
}

You can see the manual of these functions with the man 2 stat and man 2 mkdir commands.

Answer 2

You can use mkdir:

$ man 2 mkdir

#include <sys/stat.h>
#include <sys/types.h>

int result = mkdir("/home/me/test.txt", 0777);

Answer 3

I want to write a program that (...) creates the directory and a (...) file inside of it

because this is a very common question, here is the code to create multiple levels of directories and than call fopen. I'm using a gnu extension to print the error message with printf.

void rek_mkdir(char *path) {
    char *sep = strrchr(path, '/');
    if(sep != NULL) {
        *sep = 0;
        rek_mkdir(path);
        *sep = '/';
    }
    if(mkdir(path, 0777) && errno != EEXIST)
        printf("error while trying to create '%s'\n%m\n", path); 
}

FILE *fopen_mkdir(char *path, char *mode) {
    char *sep = strrchr(path, '/');
    if(sep) { 
        char *path0 = strdup(path);
        path0[ sep - path ] = 0;
        rek_mkdir(path0);
        free(path0);
    }
    return fopen(path,mode);
}

Answer 4

1. As Paul R. said you can use mkdir without stat to only use one systemcall.

2. mkdir has the errno -> EEXIST if you need the information that the directory exists.

int mkdir (const char *filename, mode_t mode)

#include <sys/types.h>
#include <errno.h>
#include <string.h>

if (mkdir("/some/directory", S_IRWXU | S_IRWXG | S_IRWXO) == -1) {
    printf("Error: %s\n", strerror(errno));
}

For best practice it is recommended to use an integer-alias for mode . The argument mode specifies the file permissions for the new directory file.

Read + Write + Execute: S_IRWXU (User), S_IRWXG (Group), S_IRWXO (Others)

Source: https://www.gnu.org/software/libc/manual/html_node/Permission-Bits.html