c - How to check whether two file names point to the same physical file

Question

I have a program that accepts two file names as arguments: it reads the first file in order to create the second file. How can I ensure that the program won't overwrite the first file?

Restrictions:

• The method must keep working when the file system supports (soft or hard) links
• File permissions are fixed and it is only required that the first file is readable and the second file writeable
• It should preferably be platform-neutral (although Linux is the primary target)

Answer 1

On linux, open both files, and use fstat to check if st_ino (edit:) and st_dev are the same. open will follow symbolic links. Don't use stat directly, to prevent race conditions.