Differentiate between a unix directory and file in C and C++

Question

Given a path, say, /home/shree/path/def, I would want to determine if def is a directory or a file. Is there a way of achieving this in C or C++ code?

Solution 1

The following code uses the stat() function and the S_ISDIR ('is a directory') and S_ISREG ('is a regular file') macros to get information on the file. The rest is just error checking and enough to make a complete compilable program.

#include <stdio.h>
#include <errno.h>
#include <sys/stat.h>

int main (int argc, char *argv[]) {
    int status;
    struct stat st_buf;

    // Ensure argument passed.

    if (argc != 2) {
        printf ("Usage: progName <fileSpec>\n");
        printf ("       where <fileSpec> is the file to check.\n");
        return 1;
    }

    // Get the status of the file system object.

    status = stat (argv[1], &st_buf);
    if (status != 0) {
        printf ("Error, errno = %d\n", errno);
        return 1;
    }

    // Tell us what it is then exit.

    if (S_ISREG (st_buf.st_mode)) {
        printf ("%s is a regular file.\n", argv[1]);
    }
    if (S_ISDIR (st_buf.st_mode)) {
        printf ("%s is a directory.\n", argv[1]);
    }

    return 0;
}

Sample runs are shown here:

pax> vi progName.c ; gcc -o progName progName.c ; ./progName
Usage: progName 
       where  is the file to check.

pax> ./progName /home
/home is a directory.

pax> ./progName .profile
.profile is a regular file.

pax> ./progName /no_such_file
Error, errno = 2

Solution 2

Use the stat(2) system call. You can use the S_ISREG or S_ISDIR macro on the st_mode field to see if the given path is a file or a directory. The man page tells you about all the other fields.

Solution 3

What about using the boost::filesystem library and its is_directory(const Path& p) ? It may take a while to get familiar with, but not so much. It probably worths the investment, and your code will not be platform specific.

Comments

[Paggas]

Problematic if filename contains whitespace, I think you'd have to escape it.

[Nathan Fellman]

your code is a bit cumbersome because of the error checking. I suggest removing this and adding some comment like "check for errors: file doesn't exist, not enough arguments". I think it'll make your answer a bit better

[Max Lybbert]

I prefer it with error checking, as that is often left out of examples and people don't necessarily know how to put it back in.

[paxdiablo]

I've left it in, but clarified in the text what the important bits are.

[Keith Smith]

While this would work, the performance will leave a lot to be desired. Every call to system() will fork and then exec a new shell to interpret the command.