CreateFile CREATE_NEW equivalent on linux

Question

I wrote a method which tries to create a file. However I set the flag CREATE_NEW so it can only create it when it doesnt exist. It looks like this:

for (;;)
  {
    handle_ = CreateFileA(filePath.c_str(), 0, 0, NULL, CREATE_NEW, FILE_ATTRIBUTE_HIDDEN | FILE_FLAG_DELETE_ON_CLOSE, NULL);
    if (handle_ != INVALID_HANDLE_VALUE)
      break;

    boost::this_thread::sleep(boost::posix_time::millisec(10));
  }

This works as it should. Now I want to port it to linux and and of course the CreateFile function are only for windows. So I am looking for something equivalent to this but on linux. I already looked at open() but I cant seem to find a flag that works like CREATE_NEW. Does anyone know a solution for this?

Answer 1

Take a look at the open() manpage, the combination of O_CREAT and O_EXCL is what you are looking for.

Example:

mode_t perms = S_IRWXU; // Pick appropriate permissions for the new file.
int fd = open("file", O_CREAT|O_EXCL, perms);
if (fd >= 0) {
    // File successfully created.
} else {
    // Error occurred. Examine errno to find the reason.
}

Answer 2

fd = open("path/to/file", O_CREAT | O_EXCL | O_RDWR | O_CLOEXEC);

O_CREAT: Creates file if it does not exist. If the file exists, this flag has no effect.
O_EXCL: If O_CREAT and O_EXCL are set, open() will fail if the file exists.
O_RDWR: Open for reading and writing.

Also, creat() is equivalent to open() with flags equal to O_CREAT|O_WRONLY|O_TRUNC.

Check this: http://linux.die.net/man/2/open

Answer 3

This is the correct and working answer:

#include <fcntl2.h> // open
#include <unistd.h> // pwrite

//O_CREAT: Creates file if it does not exist.If the file exists, this flag has no effect.
//O_EXCL : If O_CREAT and O_EXCL are set, open() will fail if the file exists.
//O_RDWR : Open for reading and writing.

int file = open("myfile.txt", O_CREAT | O_EXCL | O_RDWR | O_CLOEXEC);

if (file >= 0) {
    // File successfully created.
    ssize_t rc = pwrite(file, "your data", sizeof("myfile.txt"), 0);
} else {
    // Error occurred. Examine errno to find the reason.
}

I posted this code for another person, inside a comment because his question is closed... but this code is tested by me on Ubuntu and it's working exactly as CreateFileA and WriteFile.

It will create a new file as you are seeking.