How to create directories automatically using ofstream

Question

I am now writing an extractor for a basic virtual file system archive (without compression).

My extractor is running into problems when it writes a file to a directory that does not exist.

Extract function :

void extract(ifstream * ifs, unsigned int offset, unsigned int length, std::string path)
{
    char * file = new char[length];

    ifs->seekg(offset);
    ifs->read(file, length);

    ofstream ofs(path.c_str(), ios::out|ios::binary);

    ofs.write(file, length);
    ofs.close();

    cout << patch << ", " << length << endl;

    system("pause");

    delete [] file;
}

ifs is the vfs root file, offset is the value when the file starts, length is the file length and path is a value from file what save offsets len etc.

For example path is data/char/actormotion.txt.

Thanks.

it's not possible with an `std::ofstream`, it's for writing files only. There's probably a good wrapper for creating directories on an arbitrary platform in `boost`. — stefan, Sep 08 '13 at 09:18
@WhozCraig it will be hard because this archive had 20 000 files in different dirs. — Kacper Fałat, Sep 08 '13 at 09:18

score 33 · Answer 1 · answered Sep 08 '13 at 09:20

33

ofstream never creates directories. In fact, C++ doesn't provide a standard way to create a directory.

Your could use dirname and mkdir on Posix systems, or the Windows equivalents, or Boost.Filesystem. Basically, you should add some code just before the call to ofstream, to ensure that the directory exists by creating it if necessary.

answered Sep 08 '13 at 09:20

Steve Jessop

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+1 the note about C++ not having a standard way of making filesystem directories often comes as a shock to people. Nice to mention it. – WhozCraig Sep 08 '13 at 09:24
thanks for this. i had no idea..battled with my code for hours trying to understand what the hell happened. i could write files for days and it suddenly stopped. Didnt realize there was another piece of code which took care of folder creation.. – Alexandru Lucian Susma Mar 13 '15 at 01:20
9

[A standard way to create directories](http://en.cppreference.com/w/cpp/filesystem/create_directory) has been added along with `std::filesystem` library in C++ 17. Currently [no compiler has supported it fully and officially](http://en.cppreference.com/w/cpp/compiler_support#C.2B.2B17_features) though. – ebk Feb 15 '18 at 07:33

score 21 · Answer 2 · edited Dec 14 '19 at 10:14

21

Its not possible with ofstream to check for existence of a directory

Can use boost::filesystem::exists instead

    #include <boost/filesystem.hpp>

    boost::filesystem::path dir("path");

    if(!(boost::filesystem::exists(dir))){
        std::cout<<"Doesn't Exists"<<std::endl;

        if (boost::filesystem::create_directory(dir))
            std::cout << "....Successfully Created !" << std::endl;
    }

edited Dec 14 '19 at 10:14

Community

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answered Sep 08 '13 at 09:25

P0W

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These methods are now part of the standard and currently available under `std::experimental::filesystem` – Paul May 31 '17 at 17:14
No need for boost. – Craig B May 17 '18 at 00:06
1

`std::experimental::filesystem` is C++17. Still need to use boost for C++11 or less. – PlinioSilveira Jun 19 '18 at 17:14

score 7 · Answer 3 · answered Dec 13 '14 at 14:30

Creating a directory with ofstream is not possible. It is mainly used for files. There are two solutions below:

Solution 1:

#include <windows.h>
int _tmain() {
    //Make the directory
    system("mkdir sample");
}

Solution 2:

#include <windows.h>
int _tmain() {
    CreateDirectory("MyDir", NULL);
}

How to create directories automatically using ofstream

3 Answers3

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