Question

Windows 7 64-bit, compiling with mingw. I’m trying to test whether a given path is a directory using GetFileAttributesA in the Windows headers. The constant for something being a directory is 16. For some reason, though, it’s returning 17. My code looks like this:

#include <iostream>
#include <windows.h>

void dir_exists(std::string dir_path)
{
    DWORD f_attrib = GetFileAttributesA(dir_path.c_str());
    std::cout << "Current: " << f_attrib << std::endl <<
        "Wanted: " <<
        FILE_ATTRIBUTE_DIRECTORY << std::endl;
}

int main()
{
    dir_exists("C:\\Users\\");
    return 0;
}

When I run this, the output is:

Current: 17  
Wanted: 16

Current should be returning 16, here. As I said in the topic, I can’t even find any mention of what 17 means in the documentation.

Answer 1

GetFileAttributes returns a bitmask, the valid values for which are listed here: File Attribute Constants.

17 == 0x11, so that means the return value is
FILE_ATTRIBUTE_READONLY | FILE_ATTRIBUTE_DIRECTORY.

If you just want to detect whether your path points to a directory, mask the return value with FILE_ATTRIBUTE_DIRECTORY and see if it’s non-zero:

#include <string>
#include <iostream>
#include <windows.h>

bool dir_exists(std::string const& dir_path)
{
    DWORD const f_attrib = GetFileAttributesA(dir_path.c_str());
    return f_attrib != INVALID_FILE_ATTRIBUTES &&
           (f_attrib & FILE_ATTRIBUTE_DIRECTORY);
}

int main()
{
    std::cout << dir_exists("C:\\Users\\") << '\n';
}