If you want to get pedantic, the actual writes to the filesystem (in memory at least) are atomic in either case. However if you have not set append (or, reading some C documentation, if you're unlucky enough to be using NTFS) it is the case that one process could write to a location in the file that another process has already overwritten, thereby overwriting what the other process wrote.

So technically the writes are atomic, but the end result could still disappoint. :-)

In reply to Re^5: Append to text file not working by tilly
in thread Append to text file not working by greymoose

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