C++ - Determining if directory (not a file) exists in Linux

Question

How would I determine if a directory (not a file) existed using C++ in Linux? I tried using the stat() function but it returned positive when a file was found. I only want to find if the inputted string is a directory, not something else.

Solution 1

According to man(2) stat you can use the S_ISDIR macro on the st_mode field:

bool isdir = S_ISDIR(st.st_mode);

Side note, I would recommend using Boost and/or Qt4 to make cross-platform support easier if your software can be viable on other OSs.

Solution 2

how about something i found here

#include <dirent.h>

bool DirectoryExists( const char* pzPath )
{
    if ( pzPath == NULL) return false;

    DIR *pDir;
    bool bExists = false;

    pDir = opendir (pzPath);

    if (pDir != NULL)
    {
        bExists = true;    
        (void) closedir (pDir);
    }

    return bExists;
}

Or using stat

struct stat st;
if(stat("/tmp",&st) == 0)
    if(st.st_mode & S_IFDIR != 0)
        printf(" /tmp is present\n");

Solution 3

If you can check out the boost filesystem library. It's a great way to deal with this kind of problems in a generic and portable manner.

In this case it would suffice to use:

#include "boost/filesystem.hpp"   
using namespace boost::filesystem; 
...
if ( !exists( "test/mydir" ) ) {bla bla}

Solution 4

The way I understand your question is this: you have a path, say, /foo/bar/baz (baz is a file) and you want to know whether /foo/bar exists. If so, the solution looks something like this (untested):

char *myDir = dirname(myPath);
struct stat myStat;
if ((stat(myDir, &myStat) == 0) && (((myStat.st_mode) & S_IFMT) == S_IFDIR)) {
    // myDir exists and is a directory.
}

Solution 5

In C++17**, std::filesystem provides two variants to determine the existence of a path:

1. is_directory() determines, if a path is a directory and does exist in the actual filesystem
2. exists() just determines, if the path exists in the actual filesystem (not checking, if it is a directory)

Example (without error handling):

#include <iostream>
#include <filesystem> // C++17
//#include <experimental/filesystem> // C++14
namespace fs = std::filesystem;
//namespace fs = std::experimental::filesystem; // C++14

int main()
{
    // Prepare.
    const auto processWorkingDir = fs::current_path();
    const auto existingDir = processWorkingDir / "existing/directory"; // Should exist in file system.
    const auto notExistingDir = processWorkingDir / "fake/path";
    const auto file = processWorkingDir / "file.ext"; // Should exist in file system.

    // Test.
    std::cout
        << "existing dir:\t" << fs::is_directory(existingDir) << "\n"
        << "fake dir:\t" << fs::is_directory(notExistingDir) << "\n"
        << "existing file:\t" << fs::is_directory(file) << "\n\n";

    std::cout
        << "existing dir:\t" << fs::exists(existingDir) << "\n"
        << "fake dir:\t" << fs::exists(notExistingDir) << "\n"
        << "existing file:\t" << fs::exists(file);
}

Possible output:

existing dir:   1
fake dir:       0
existing file:  0

existing dir:   1
fake dir:       0
existing file:  1

**in C++14 std::experimental::filesystem is available

---

Both functions throw filesystem_error in case of errors. If you want to avoid catching exceptions, use the overloaded variants with std::error_code as second parameter.

#include <filesystem>
#include <iostream>
namespace fs = std::filesystem;

bool isExistingDir(const fs::path& p) noexcept
{
    try
    {
        return fs::is_directory(p);
    }
    catch (std::exception& e)
    {
        // Output the error message.
        const auto theError = std::string{ e.what() };
        std::cerr << theError;

        return false;
    }
}

bool isExistingDirEC(const fs::path& p) noexcept
{
    std::error_code ec;
    const auto isDir = fs::is_directory(p, ec);
    if (ec)
    {
        // Output the error message.
        const auto theError = ec.message();
        std::cerr << theError;

        return false;
    }
    else
    {
        return isDir;
    }
}

int main()
{
    const auto notExistingPath = fs::path{ "\xa0\xa1" };
    isExistingDir(notExistingPath);
    isExistingDirEC(notExistingPath);
}

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