[PDF] fopen exclusive mode

What does fopen do?

The fopen () function opens the file whose name is the string pointed to by pathname and associates a stream with it. The argument mode points to a string beginning with one of the following sequences (possibly followed by additional characters, as described below): r Open text file for reading.

Is fopen preferred over open?

Based on Stack Overflow question C fopen vs open, fopen is preferred over open. How can I implement my own file lock (if possible) by creating and deleting lock files? I would strongly disagree with the claim that fopen is prefered over open.

What is append file access mode?

On the append file access modes, data is written to the end of the file regardless of the current position of the file position indicator. File access mode flag "x" can optionally be appended to "w" or "w+" specifiers. This flag forces the function to fail if the file exists, instead of overwriting it. (C++17)

Is it safe to use fopen if a file is writable?

It's impossible to use fopen safely when writing a file in a directory that's writable by other users due to symlink vulnerabilities/race conditions, since there is no O_EXCL option. If you need to use stdio on POSIX systems, it's best to use open and fdopen rather than calling fopen directly. Now, as for locking it depends on what you want to do.