Reading a directory

Answer 1

There's nothing like that in windows. If you want to enumerate a directory in Windows, you must use the FindFirstFile/FindNextFile API.

Answer 2

Yes, this works on Linux/Unix only. However if you are just playing around you may use Cygwin to build programs on Windows that use this Unix API.

Answer 3

boost::filesystem::directory_iterator provides a portable equivalent of Windows FindFirstFile/FindNextFile API and POSIX readdir_r() API. See this tutorial.

Note that this is C++ not plain C.

cheers, AR

Answer 4

It is interesting to note that you are using K&R 1st Edition, from 1978, and not the second edition. The second edition has different structures, etc, at that point in the book.

That code from the first edition does not work on many Unix-like systems any more. There are very few Unix machines left with file systems that restrict file names to the 14-character limit, and that code only works on those systems. Specifically, it does not work on MacOS X (10.6.2) or Solaris (10) or Linux (SuSE Linux Enterprise Edition 10, kernel 2.6.16.60-0.21-smp). With the test code shown below, the result is:

read failed: (21: Is a directory)

Current editions of POSIX explicitly permit the implementation to limit what you can do with a file descriptor opened on a directory. Basically, it can be used in the 'fchdir()' system calls and maybe a few relatives, but that is all.

To read the contents of the directory, you have to use the opendir() family of functions, and then readdir() etc. The second edition of K&R goes on to use these system calls instead of raw open() and read() etc.

All-in-all, it is not dreadfully surprising that code from over 30 years ago doesn't quite work the same as it used to.

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On Windows, you can either use the POSIX sub-system or an emulation of that such as Cygwin or MingW, and in either case you will need to use the opendir() and readdir() family of function calls, not direct open() and read() on the directory file descriptor.

Or you can use the native Windows API that BillyONeal references, FindFirstFile and relatives.

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Test code:

#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>

int main()
{
    int fd = open(".", O_RDONLY);
    if (fd != -1)
    {
        char buffer[256];
        ssize_t n = read(fd, buffer, sizeof(buffer));
        if (n < 0)
        {
            int errnum = errno;
            printf("read failed: (%d: %s)\n", errnum, strerror(errnum));
        }
        else
            printf("read OK: %d bytes (%s)\n", (int)n, buffer);
        close(fd);
    }
    return(0);
}