CS253: Software Development with C++

Spring 2018

Compiled Header Files

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CS253 Compiled Header Files

Simple Example

Consider this simple program. It gets π from a header file:

    % cat main.cc
    #include "pi.h"
    #include <iostream>
    int main() {
        std::cout << pi << '\n';
        return 0;
    % cat pi.h
    constexpr auto pi = 3.14;
    % g++ -Wall main.cc
    % ./a.out
    % ls
    a.out  main.cc  pi.h

Note that pi.h is not mentioned in the compile command.

What if we try to compile pi.h?

    % g++ -Wall main.cc pi.h
    % ls
    a.out  main.cc  pi.h  pi.h.gch
    % ./a.out
Let’s improve the value of π:
    % echo "constexpr auto pi = 3.14159;" >pi.h
    % g++ -Wall main.cc 
    % ./a.out
Hey, why didn’t it work?
    % rm pi.h.gch 
    % g++ -Wall main.cc 
    % ./a.out

Moral of the story

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Modified: 2018-04-24T16:51

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