Using the open() system call

Question

I'm writing a program that writes output to a file. If this file doesn't exist, I want to create it.

Currently, I'm using the following flags when calling open: O_WRONLY | O_CREATE

However, when this creates the file, it doesn't give me any permissions to write to it...

How can I use open so that it creates a file if it doesn't exist, but will create it with necessary permissions when needed?

Thanks!

Answer 1

You probably need the third argument. For example:

open('path',O_WRONLY|O_CREAT,0640);

Answer 2

Just use the optional third argument to open:

int open(const char* pathname, int flags, mode_t mode);

so like this:

open("blahblah", O_CREAT | O_WRONLY, S_IRUSR | S_IWUSER | S_IRGRP | S_IROTH);

See man open(2).