How to create directory c++ (using _mkdir)

Question

Today I did a lot of research online about how to create a directory on C++ and found a lot of way to do that, some easier than others.

I tried the _mkdir function using _mkdir("C:/Users/..."); to create a folder. Note that the argument of function will be converted into a const char*.

So far, so good, but when I want to change the path, it does not work (see the code below). I have a default string path "E:/test/new", and I want to create 10 sub-folders: new1, new2, newN, ..., new10.

To do that, I concatenate the string with a number (the counter of the for-loop), converted into char using static_cast, then I transform the string using c_str(), and assign it to a const char* variable.

The compiler has no problem compiling it, but it doesn't work. It prints 10 times "Impossible create folder n". What's wrong?

I probably made a mistake when transforming the string using c_str() to a get a const char*?.

Also, is there a way to create a folder using something else? I looked at CreateDirectory(); (API) but it uses keyword like DWORD HANDLE, etc., that are a little bit difficult to understand for a no-advanced level (I don't know what these mean).

#include <iostream>
#include <Windows.h>
#include<direct.h>

using namespace std;

int main()
{
int stat;
string path_s = "E:/test/new";

for (int i = 1; i <= 10; i++)
{
    const char* path_c = (path_s + static_cast<char>(i + '0')).c_str();
    stat = _mkdir(path_c);

    if (!stat)
        cout << "Folder created " << i << endl;
    else
        cout << "Impossible create folder " << i << endl;
    Sleep(10);
}
return 0;
}

i + '0' won't work very well when i == 10. Perhaps you should use std::to_string instead? — Some programmer dude
– Some programmer dude, Commented Aug 5, 2019 at 12:38
And the Windows CreateDirectoryA function is really easy to use: Pass the path as the first argument, and a null pointer as the second. — Some programmer dude
– Some programmer dude, Commented Aug 5, 2019 at 12:41
You might be interested in new (C++17) file system library, you wouldn't rely on (non-standard!) mkdir any more... — Aconcagua
– Aconcagua, Commented Aug 5, 2019 at 12:42
Does "E:/test" exist? I'm pretty sure _mkdir will only create one level of directory. — Martin Bonner supports Monica
– Martin Bonner supports Monica, Commented Aug 5, 2019 at 13:04

Kaldrr · Accepted Answer · 2019-08-05 12:44:58Z

11

If your compiler supports c++17, you can use filesystem library to do what you want.

#include <filesystem>
#include <string>
#include <iostream>

namespace fs = std::filesystem;

int main(){
    const std::string path = "E:/test/new";
    for(int i = 1; i <= 10; ++i){
        try{
            if(fs::create_directory(path + std::to_string(i)))
                std::cout << "Created a directory\n";
            else
                std::cerr << "Failed to create a directory\n";\
        }catch(const std::exception& e){
            std::cerr << e.what() << '\n';
        }
    }
    return 0;
}

answered Aug 5, 2019 at 12:44

Kaldrr

2,87011 silver badges13 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Some programmer dude · Accepted Answer · 2019-08-05 12:44:11Z

4

The problem is that (path_s + static_cast<char>(i + '0')) creates a temporary object. One whose life-time ends (and is destructed) just after c_str() has been called.

That leaves you with a pointer to a string that no longer exist, and using it in almost any way will lead to undefined behavior.

Instead save the std::string object, and call c_str() just when needed:

std::string path = path_s + std::to_string(i);
_mkdir(path.c_str());

answered Aug 5, 2019 at 12:44

Some programmer dude

411k36 gold badges420 silver badges655 bronze badges

Comments

Owl · Accepted Answer · 2019-08-05 13:37:01Z

2

Note that under Linux, you can use the mkdir command as follows:

#include <sys/stat.h>
... 
const int dir_err = mkdir("foo", S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH);
if (-1 == dir_err){
    printf("Error creating directory!n");
    exit(1);
}

More information on it can be gleaned from reading man 2 mkdir.

answered Aug 5, 2019 at 13:37

Owl

1,59115 silver badges22 bronze badges

Collectives™ on Stack Overflow

How to create directory c++ (using _mkdir)

3 Answers 3

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related