Determine the size of a pipe without calling read()

Question

I need a function called SizeOfPipe() which should return the size of a pipe - I only want to know how much data is in the pipe and not actually read data off t

Answer 1

It's almost never necessary to know how many bytes are in the pipe: perhaps you just want to do a non-blocking read() on the pipe, ie. to check if there are any bytes ready, and if so, read them, but never stop and wait for the pipe to be ready.

You can do that in two steps. First, use the select() system call to find out whether data is available or not. An example is here: http://www.developerweb.net/forum/showthread.php?t=2933

Second, if select tells you data is available, call read() once, and only once, with a large block size. It will read only as many bytes are available, or up to the size of your block, whichever is smaller. If select() returns true, read() will always return right away.