Read and write to a file while keeping lock

Question

I am making a simple page load counter by storing the current count in a file. This is how I want to do this:

1. Lock the file (flock)
2. Read the current c

Answer 1

Yes, you have to use rewind before ftruncate. Otherwise, the old content of the file is only refilled with zeros.

The working sequence is:

    fopen
    flock LOCK_EX
    fread filesize
    rewind
    ftruncate 0
    fwrite 
    flock LOCK_UN
    fclose