Opposite of O_CREAT|O_EXCL

Question

Is there way in C on Linux to only write to a file if it already exists? In other words, the opposite of open(..., O_CREAT|O_EXCL) .

Note that I don't want the existence check decoupled from the actual opening of the file (like calling stat() beforehand) because that would be a race condition.

Answer 1

To do this I would try to open the file with O_WRONLY, if open() doesn't fail, the file exists. You can check errno to check the error.

I don't know any other way.

Answer 2

Check for ENOENT while trying to open the file without the O_CREAT flag.

ENOENT O_CREAT is not set and the named file does not exist; or O_CREAT is set and either the path prefix does not exist or the path argument points to an empty string.

Answer 3

If you can use fopen , then:

file=fopen(some_sime, "r+");
if (file) fd=fileno(file);