Building a library

Starting from the bottom up, we'll build a library and then use that library in the next example.

We will have 3 files in this layout.

| Layout              | Description
|---------------------|----------------------------------
| root/               |
|   include/          |
|     lib.h           | 1. Definition of a sample function
|   src/              |
|     lib.cpp         | 2. Declaration of function
|     main.cpp        | 3. Use of library
|   build/            |
|     ...             | Output goes here

Here is the content of each file.

lib.h

namespace mynamespace
{
    void helloWorld();
}

lib.cpp

#include <iostream>
#include "lib.h"

namespace mynamespace
{
    void helloWorld()
    {
        std::cout << "Hello World!" << std::endl;
    }
}

main.cpp

#include "lib.h"

int main(void)
{
    mynamespace::helloWorld();
    return(0);
}

Compile

Before compiling anything, you will need to setup your environment.

term.bat

set PATH=C:\Program Files (x86)\Microsoft Visual Studio 12.0\Common7\IDE;%PATH%
call "c:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\vcvarsall.bat" x86
cmd /K cls

Exchange 12.0 with 14.0 for Visual Studio 2015.

build-lib.bat

This will output build/lib.lib.

@echo off
pushd build

cl^
  -Zi^
  -EHsc^
  -I "..\include"^
  -c^
  ..\src\lib.cpp &&^
lib^
  lib.obj

popd

build.bat

This will use build/lib.lib to compile a console application.

Notice the similarities between compilation, and differing second command; from lib.exe to link.exe.

@echo off
pushd build

cl^
  -Zi^
  -EHsc^
  -I "..\include"^
  -c^
  ..\src\main.cpp &&^
link main.obj^
  lib.lib^
  /LIBPATH:"..\build"

popd

Running

Now that you are done, you can run your program.

> build\main.exe
Hello World!

This program is:

1. Calling a function defined in lib.h.
2. Which is defined in lib.cpp
3. And provided to our application via lib.lib

You will note that if you excluded lib.lib from your build.bat script, an error is thrown.

main.obj : error LNK2019: unresolved external symbol "void __cdecl mynamespace::hello
World(void)" (?helloWorld@mynamespace@@YAXXZ) referenced in function _main
main.exe : fatal error LNK1120: 1 unresolved externals