Create a directory if it doesn't exist

Question

In my app I want to copy a file to the other hard disk so this is my code:

 #include <windows.h>

using namespace std;

int main(int argc, char* argv[] )
{
    string Input = "C:\\Emploi NAm.docx";
    string CopiedFile = "Emploi NAm.docx";
    string OutputFolder = "D:\\test";
    CopyFile(Input.c_str(), string(OutputFolder+CopiedFile).c_str(), TRUE);

    return 0;
}

so after executing this, it shows me in the D:HDD a file testEmploi NAm.docx but I want him to create the test folder if it doesn't exist.

I want to do that without using the Boost library.

hmjd · Accepted Answer · 2012-02-10T22:39:09.777

87

Use the WINAPI CreateDirectory() function to create a folder.

You can use this function without checking if the directory already exists as it will fail but GetLastError() will return ERROR_ALREADY_EXISTS:

if (CreateDirectory(OutputFolder.c_str(), NULL) ||
    ERROR_ALREADY_EXISTS == GetLastError())
{
    // CopyFile(...)
}
else
{
     // Failed to create directory.
}

The code for constructing the target file is incorrect:

string(OutputFolder+CopiedFile).c_str()

this would produce "D:\testEmploi Nam.docx": there is a missing path separator between the directory and the filename. Example fix:

string(OutputFolder+"\\"+CopiedFile).c_str()

edited Feb 10 '12 at 22:39

answered Feb 10 '12 at 22:28

hmjd

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thanks for fast answer so how can i mix it with the CopyFile member – pourjour Feb 10 '12 at 22:32
Prior to calling `CopyFile()` call `CreateDirectory()` to create `OutputFolder`. – hmjd Feb 10 '12 at 22:34
Does this function gets "ERROR_ALREADY_EXISTS" if path is just "C:\" ? Thanks – Keshava GN May 18 '17 at 13:41
4

[For those who reach the error](https://stackoverflow.com/questions/33001284/incompatible-with-parametr-of-type-lpcwstr) `argument of type "const char *" is incompatible with parameter of type "LPCWSTR"`. – baru Jun 23 '17 at 07:51
Small caveat: CreateDirectory also returns if lpPathName points to an existing *file* so one might wrongly assume it is a directory, and in this case the CopyFile call would probably fail – stijn Mar 28 '18 at 18:57
There is an issue with this solution I think, because you need to include the windows.h library which has a lot of macros that ignore scope. This can make it completely incompatible with other libraries. – Elliott May 28 '19 at 10:59
1

@baru if you get LPCWSTR you can change the function **CreateDirectory** to **CreateDirectoryA** – Ruben Medrano Apr 17 '21 at 17:19

Vertexwahn · Answer 2 · 2021-01-08T22:02:53.680

66

#include <experimental/filesystem> // or #include <filesystem> for C++17 and up
    
namespace fs = std::experimental::filesystem;


if (!fs::is_directory("src") || !fs::exists("src")) { // Check if src folder exists
    fs::create_directory("src"); // create src folder
}

edited Jan 08 '21 at 22:02

answered May 30 '16 at 10:59

Vertexwahn

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5

Just need to compile with -lstdc++fs – Victor.dMdB Jan 24 '17 at 09:30
1

The logic is flawed if "src" points to a file instead of a directory, you should add a call to is_directory (or whatever it is called) – stijn Mar 28 '18 at 18:58
@stijn Fixed it! ;) – Vertexwahn Mar 29 '18 at 21:58
2

It is in C++17 now – Ji Fang Jun 13 '20 at 00:56
Updated the answer to reflect modern C++17 and up – StarShine Jan 07 '21 at 09:29
11

You don't need the `if` at all. Just do `fs::create_directory`, and if the directory already exists, it won't do anything. – HolyBlackCat Jan 08 '21 at 22:05
Is this platform agnostic? – tzg Jul 16 '21 at 16:19
2

@tzg Yes. C++17 and up provide a [Filesystem library](https://en.cppreference.com/w/cpp/filesystem). – Vertexwahn Jul 16 '21 at 20:25
As HolyBlackCat mentioned, we don't need `if`. Moreover, `std::filesystem::create_directory` returns `true` if it creates the directory(not exist one), else returns `false`. Also, use `create_directories` to create nested directories like `path/to/nested/dir`. – starriet Oct 13 '22 at 15:43

score 42 · Answer 3 · edited Jan 17 '18 at 14:40

42

Probably the easiest and most efficient way is to use boost and the boost::filesystem functions. This way you can build a directory simply and ensure that it is platform independent.

const char* path = _filePath.c_str();
boost::filesystem::path dir(path);
if(boost::filesystem::create_directory(dir))
{
    std::cerr<< "Directory Created: "<<_filePath<<std::endl;
}

boost::filesystem::create_directory - documentation

edited Jan 17 '18 at 14:40

Gelldur

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answered Jul 29 '14 at 11:17

Chris Rayner

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3

Which headers do you need to use here? – vegetus Jul 11 '16 at 18:54
5

For Googlers like myself, `#include ` Also, pass `-lboost_filesystem -lboost_system` to the linker – hewy Jul 05 '17 at 18:30

Fivee Arch · Answer 4 · 2014-03-04T20:44:16.757

21

Here is the simple way to create a folder.......

#include <windows.h>
#include <stdio.h>

void CreateFolder(const char * path)
{   
    if(!CreateDirectory(path ,NULL))
    {
        return;
    }
}


CreateFolder("C:\\folder_name\\")

This above code works well for me.

edited Mar 04 '14 at 20:44

answered Mar 04 '14 at 20:15

Fivee Arch

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24

Thanks for including the .h file reference, which for us newbies is hard to determine. – John Sep 09 '15 at 19:58
1

There is an issue with this solution I think, because the windows.h library has a lot of macros that ignore scope. This can make it completely incompatible with other libraries. – Elliott May 28 '19 at 11:22

score 10 · Answer 5 · answered Mar 05 '15 at 11:31

10

_mkdir will also do the job.

_mkdir("D:\\test");

https://msdn.microsoft.com/en-us/library/2fkk4dzw.aspx

answered Mar 05 '15 at 11:31

leoly

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With ref. to the asked question, use `_mkdir(OutputFolder.c_str())`. – Ruchir Apr 19 '16 at 08:31

Eike · Answer 6 · 2023-08-10T22:58:55.607

9

Since c++17, you can easily do this cross-platform with:

#include <filesystem>
int main() {
bool created_new_directory = false;
bool there_was_an_exception = false;

try {
  created_new_directory
      = std::filesystem::create_directory("directory_name");
} catch(std::exception & e){
there_was_an_exception = true;
// creation failed
}
if ((not created_new_directory) and (not there_was_an_exception)) {
    // no failure, but the directory was already present.
  }
}

Note, that this version is very useful, if you need to know, whether the directory is actually newly created. And I find the documentation on cppreference slightly difficult to understand on this point: If the directory is already present, this function returns false.

This means, you can more or less atomically create a new directory with this method.

edited Aug 10 '23 at 22:58

answered Jan 13 '22 at 13:47

Eike

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Is the directory creation guaranteed to be atomic? Just asking because I couldn't find such information on cppreference.com. – starriet Oct 13 '22 at 10:02
1

No, therefore the "more or less". It depends on the operating system and cannot be guaranteed by c++. I think it is atomic in POSIX systems if using local filesystems (not over network), but don't quote me on that. Although I have used this on Linux and not gotten a failure of atomicity, yet. – Eike Oct 14 '22 at 11:10

saurabheights · Answer 7 · 2019-08-15T16:51:27.363

6

OpenCV Specific

Opencv supports filesystem, probably through its dependency Boost.

#include <opencv2/core/utils/filesystem.hpp>
cv::utils::fs::createDirectory(outputDir);

edited Aug 15 '19 at 16:51

answered Dec 27 '18 at 17:54

saurabheights

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P.S. - This answer helps mostly students/researchers who have to work on computer vision projects but do not need Boost specifically. – saurabheights Dec 27 '18 at 17:55
Does this function destroy the folder if it exists? – KansaiRobot Dec 23 '21 at 01:21
1

@KansaiRobot https://github.com/opencv/opencv/blob/17234f82d025e3bbfbf611089637e5aa2038e7b8/modules/core/src/utils/filesystem.cpp#L232 It just emulates linux mkdir command. So if a folder already exists, it returns true. No directory should get deleted. – saurabheights Dec 23 '21 at 04:13

driedler · Answer 8 · 2021-03-25T22:27:35.623

3

This works in GCC:

Taken from: Creating a new directory in C

#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);
}

edited Mar 25 '21 at 22:27

answered Mar 25 '21 at 21:46

driedler

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score 3 · Answer 9 · edited May 30 '16 at 11:02

3

Use CreateDirectory (char *DirName, SECURITY_ATTRIBUTES Attribs);

If the function succeeds it returns non-zero otherwise NULL.

edited May 30 '16 at 11:02

Vertexwahn

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answered Feb 10 '12 at 22:34

DotNetUser

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score 2 · Answer 10 · answered Jul 06 '17 at 07:18

2

You can use cstdlib

Although- http://www.cplusplus.com/articles/j3wTURfi/

#include <cstdlib>

const int dir= system("mkdir -p foo");
if (dir< 0)
{
     return;
}

you can also check if the directory exists already by using

#include <dirent.h>

answered Jul 06 '17 at 07:18

Noa Yehezkel

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this isn't portable, as `-p` option doesn't work with windows mkdir version. – Jean-François Fabre Feb 07 '18 at 16:22

Create a directory if it doesn't exist

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