Why use precompiled headers (C/C++)?

Question

Why use precompiled headers?

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Reading the responses, I suspect what I\'ve been doing with them is kind of stupid:

#pragma once

// Defines used         


        

Answer 1

In C/C++, the #include mechanism is a textual copy of the file specified into the current file. Headers include other headers (which include yet other headers), so when you do a #include, it could be adding tens of thousands of lines of C++ into each cpp file (or cxx, c, whatever), all of which need to be compiled each time. This can be a sever bottleneck for large projects.

Precompiled headers speed this up by compiling each header once, then including that compiled state into the cpp they are included in.