Building a Static 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

build-lib.sh

This will output lib/lib.lib.

#!/usr/bin/env bash

mkdir -p build
pushd build

clang++ \
    -c \
    -Wall \
    -o lib.o \
    -I ../include \
    ../src/lib.cpp && \

llvm-ar \
    rc ../lib/lib.a \
    lib.o

popd

build.sh

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

#!/usr/bin/env bash

mkdir -p build
pushd build

clang++ \
    -Wall \
    -o main \
    -I ../include \
    ../src/main.cpp \
    ../lib/lib.a

popd

Running

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

$ build\main
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.

/tmp/main-05a698.o: In function `main':
../src/main.cpp:(.text+0x10): undefined reference to `mynamespace::helloWorld()'
clang: error: linker command failed with exit code 1 (use -v to see invocation)