Create folder if it doesn't exist, do nothing if it does

Question

I want to create a folder named sessionname. If a folder with this name already exists it is fine, and I don't want to do anything.

Right now I do this:

finalpath = "/home/Documents"    
finalpath.append(path + "/" + sessionname);
    if (mkdir(finalpath.c_str(), S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH) == -1)
    {
        //INVALID PATH
        std::cout << "path is invalid, cannot create sessionnamefolder" << std::endl;
        throw std::exception();
    }

This code errors, if the folder /home/Documents/sessionname exists because the folder couldn't be created.

How can I check if mkdir fails because the string was invalid or because the string was vaild but the folder already exists ?

Read http://pubs.opengroup.org/onlinepubs/009695399/functions/mkdir.html — , Mar 11 '16 at 14:19
http://stackoverflow.com/questions/7430248/creating-a-new-directory-in-c — Julien Lopez, Mar 11 '16 at 14:19
Have you read [the `mkdir` manual page](http://man7.org/linux/man-pages/man2/mkdir.2.html)? Have you checked what errors you can get from it? — Some programmer dude, Mar 11 '16 at 14:20

Slava · Accepted Answer · 2020-09-11T13:17:40.900

5

How can I check if mkdir fails because the string was invalid or because the string was vaild but the folder already existed?

Return code from mkdir() shows if function is successful or not. In case of failure you should check special variable errno, details can be found on man page

if (mkdir(finalpath.c_str(), S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH) == -1)
{
    if( errno == EEXIST ) {
       // alredy exists
    } else {
       // something else
        std::cout << "cannot create sessionnamefolder error:" << strerror(errno) << std::endl;
        throw std::runtime_error( strerror(errno) );
    }
}

Note: this is common method for Linux/Unix (and other POSIX systems) library functions to report details of error condition.

edited Sep 11 '20 at 13:17

answered Mar 11 '16 at 14:43

Slava

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you need to include for S_IRWXU, S_IRWXG . – VHanded Jul 22 '19 at 03:48
Did you mean `std::runtime_error` instead of `std::runtime_exception`? – Gavriil Pascalau Sep 11 '20 at 08:46
I cannot find any documentation that goes over a directory already existing, but exists with different permissions than your call to mkdir. – JoeManiaci May 24 '21 at 21:03
Downvote because OP said not to throw an error only if folder exists with the same name. But this code will not throw an error if a file exists with the same name. – C. Lang Oct 27 '22 at 17:17

score 1 · Answer 2 · edited May 23 '17 at 12:22

1

As commented, it's mentioned on the mkdir - make a directory - manual page, one of the errors mkdir can get you is if [EEXIST] -> The named file exists. So it fails. See here for the mkdir main page. And here is a possible duplicate on stackoverflow.

edited May 23 '17 at 12:22

Community

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answered Mar 11 '16 at 14:28

Khalil Khalaf

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Probably OP does not know where to get that error code from. – Slava Mar 11 '16 at 14:37

Create folder if it doesn't exist, do nothing if it does

2 Answers2