How can I create directory tree in C++/Linux?

Question

I want an easy way to create multiple directories in C++/Linux.

For example I want to save a file lola.file in the directory:

/tmp/a/b/c

but if the directories are not there I want them to be created automagically. A working example would be perfect.

Answer 1

Since this post is ranking high in Google for "Create Directory Tree", I am going to post an answer that will work for Windows — this will work using Win32 API compiled for UNICODE or MBCS. This is ported from Mark's code above.

Since this is Windows we are working with, directory separators are BACK-slashes, not forward slashes. If you would rather have forward slashes, change '\\' to '/'

It will work with:

c:\foo\bar\hello\world

and

c:\foo\bar\hellp\world\

(i.e.: does not need trailing slash, so you don't have to check for it.)

Before saying "Just use SHCreateDirectoryEx() in Windows", note that SHCreateDirectoryEx() is deprecated and could be removed at any time from future versions of Windows.

bool CreateDirectoryTree(LPCTSTR szPathTree, LPSECURITY_ATTRIBUTES lpSecurityAttributes = NULL){
    bool bSuccess = false;
    const BOOL bCD = CreateDirectory(szPathTree, lpSecurityAttributes);
    DWORD dwLastError = 0;
    if(!bCD){
        dwLastError = GetLastError();
    }else{
        return true;
    }
    switch(dwLastError){
        case ERROR_ALREADY_EXISTS:
            bSuccess = true;
            break;
        case ERROR_PATH_NOT_FOUND:
            {
                TCHAR szPrev[MAX_PATH] = {0};
                LPCTSTR szLast = _tcsrchr(szPathTree,'\\');
                _tcsnccpy(szPrev,szPathTree,(int)(szLast-szPathTree));
                if(CreateDirectoryTree(szPrev,lpSecurityAttributes)){
                    bSuccess = CreateDirectory(szPathTree,lpSecurityAttributes)!=0;
                    if(!bSuccess){
                        bSuccess = (GetLastError()==ERROR_ALREADY_EXISTS);
                    }
                }else{
                    bSuccess = false;
                }
            }
            break;
        default:
            bSuccess = false;
            break;
    }

    return bSuccess;
}

Answer 2

You said "C++" but everyone here seems to be thinking "Bash shell."

Check out the source code to gnu mkdir; then you can see how to implement the shell commands in C++.

Answer 3

mkdir -p /dir/to/the/file

touch /dir/to/the/file/thefile.ending

Answer 4

If dir does not exist, create it:

boost::filesystem::create_directories(boost::filesystem::path(output_file).parent_path().string().c_str()); 

Answer 5

system("mkdir -p /tmp/a/b/c")

is the shortest way I can think of (in terms of the length of code, not necessarily execution time).

It's not cross-platform but will work under Linux.

Answer 6

This is similar to the previous but works forward through the string instead of recursively backwards. Leaves errno with the right value for last failure. If there's a leading slash, there's an extra time through the loop which could have been avoided via one find_first_of() outside the loop or by detecting the leading / and setting pre to 1. The efficiency is the same whether we get set up by a first loop or a pre loop call, and the complexity would be (slightly) higher when using the pre-loop call.

#include <iostream>
#include <string>
#include <sys/stat.h>

int
mkpath(std::string s,mode_t mode)
{
    size_t pre=0,pos;
    std::string dir;
    int mdret;

    if(s[s.size()-1]!='/'){
        // force trailing / so we can handle everything in loop
        s+='/';
    }

    while((pos=s.find_first_of('/',pre))!=std::string::npos){
        dir=s.substr(0,pos++);
        pre=pos;
        if(dir.size()==0) continue; // if leading / first time is 0 length
        if((mdret=mkdir(dir.c_str(),mode)) && errno!=EEXIST){
            return mdret;
        }
    }
    return mdret;
}

int main()
{
    int mkdirretval;
    mkdirretval=mkpath("./foo/bar",0755);
    std::cout << mkdirretval << '\n';

}