= Static Library
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# Introduction

Shows a hello world example which first creates and links a static library

The files in this tutorial are below:

```
$ tree
.
├── CMakeLists.txt
├── inc
│   └── Hello.h
└── src
    ├── Hello.cpp
    └── main.cpp
```

  * CMakeLists.txt - Contains the CMake commands you wish to run
  * inc/Hello.h - The header file to include
  * src/Hello.cpp - A source file to compile
  * src/main.cpp - The source file with main


# Concepts

## Adding a Static Library

The +add_library()+ function is used to create a library from some source files.
This is called as follows:

[source,cmake]
----
set(library_SOURCES
    src/Hello.cpp
)

add_library(hello_library STATIC ${library_SOURCES})
----

This will be used to create a static library with the name libhello_library.a with
the sources from the +library_SOURCES+ variable.

## Linking a Library

When creating an executable that will use your library you must tell the compiler
about the library. This can be done using the +target_link_library()+ function.

[source,cmake]
----
add_executable(hello_binary ${binary_SOURCES})

target_link_libraries( hello_binary
    hello_library
)
----

This tells CMake to link the hello_library against the hello_binary executable
during link time.

An example of this being called by the compiler is

```
/usr/bin/c++ CMakeFiles/hello_binary.dir/src/main.cpp.o -o hello_binary -rdynamic libhello_library.a
```


# Building the Example

[source,bash]
----
$ mkdir build

$ cd build

$ cmake ..
-- The C compiler identification is GNU 4.8.4
-- The CXX compiler identification is GNU 4.8.4
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Configuring done
-- Generating done
-- Build files have been written to: /home/matrim/workspace/cmake-examples/01-basic/C-static-library/build

$ make
Scanning dependencies of target hello_library
[ 50%] Building CXX object CMakeFiles/hello_library.dir/src/Hello.cpp.o
Linking CXX static library libhello_library.a
[ 50%] Built target hello_library
Scanning dependencies of target hello_binary
[100%] Building CXX object CMakeFiles/hello_binary.dir/src/main.cpp.o
Linking CXX executable hello_binary
[100%] Built target hello_binary

$ ls
CMakeCache.txt  CMakeFiles  cmake_install.cmake  hello_binary  libhello_library.a  Makefile

$ ./hello_binary
Hello Static Library!
----
