Hi everybody!

This blog is about speeding up C/C++ compilers with precompiled headers.

Including lots of headers or big headers like bits/stdc++.h will increase compilation time. This can be annoying even with high speed processors. We can solve this using precompiled headers.

What are precompiled headers?

You can compile a header like stdc++.h to stdc++.h.gch and compiler will use it instead of compiling the header every time you are compiling your code. Less processing => Less time.

How to use precompiled headers?

1. Find your g++ default include directory

   • Ubuntu: /usr/include/x86_64-linux-gnu/c++/{version}
   • Windows: C:\MinGW\lib\gcc\mingw32\{version}\include\c++

2. Compile headers you need (I recommend using bits/stdc++.h instead of including lots of headers).

   g++ {header name} {flags you use when compiling a normal code}

3. Put .gch files in the right place. You have 2 Options:

   • Put them in the directory you find the headers & use #include <header name>
   • Put them in your code directory & use #include "header name"

   I recommend first options because the second one will work only when .gch files are in the code directory and it takes a little extra time to search in code.

Compile a code and feel the difference!

Comment your issues or suggestions.

Be good and code fast ;)