3.4. creat Function

A new file can also be created by calling the creat function.

#include <fcntl.h> int creat(const char *pathname, mode_t mode);
Returns: file descriptor opened for write-only if OK, 1 on error

Note that this function is equivalent to

    open (pathname, O_WRONLY | O_CREAT | O_TRUNC, mode);

Historically, in early versions of the UNIX System, the second argument to open could be only 0, 1, or 2. There was no way to open a file that didn't already exist. Therefore, a separate system call, creat, was needed to create new files. With the O_CREAT and O_TRUNC options now provided by open, a separate creat function is no longer needed.

We'll show how to specify mode in Section 4.5 when we describe a file's access permissions in detail.

One deficiency with creat is that the file is opened only for writing. Before the new version of open was provided, if we were creating a temporary file that we wanted to write and then read back, we had to call creat, close, and then open. A better way is to use the open function, as in

    open (pathname, O_RDWR | O_CREAT | O_TRUNC, mode);