How to create a file only if it doesn't exist?

Question

I wrote a UNIX daemon (targeting Debian, but it shouldn\'t matter) and I wanted to provide some way of creating a \".pid\" file, (a file which contains the process identifie

Answer 1

One way to approach this problem is to open the file for appending. If the function succeeds and the position is at 0 then you can be fairly certain this is a new file. Could still be an empty file but that scenario may not be important.

FILE* pFile = fopen(theFilePath, "a+");
if (pFile && gfetpos(pFile) == 0) { 
  // Either file didn't previously exist or it did and was empty

} else if (pFile) { 
  fclose(pFile);
}