CMake
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# Cmake

# Adding Libraries

Often times, it is needed to use libraries to make the program happen.

Cmake offers easy functions to use libraries.

In this example, we will use a common library: **SQLite3**. This project will be called **TestSQL** and will be a totally useless code except for demonstrating how to link libraries with cmake. This tutorial assumes you know how to install your desired libraries.

## Structure

Same directories structure as before. We will have our project folder called **testSQL** with 2 other folders inside named **sources** and **includes**.

In the terminal:
```
mkdir ./TestSQL/sources ./TestSQL/includes
cd ./TestSQL
```
## The Source

We need to create and edit a file, inside the TestSQL/sources folder, named **main.cpp** like this: 

```
//main.cpp
#include < iostream >
#include < sqlite3.h >

using namespace std;

int main(){
    sqlite3 *db;
    int status=sqlite3_open("test.db",&db);
    if(status){
        cout << "Could not connect "
                "to database" << endl;
    }else{
        cout << "Connected to database"
             << endl;
    }
    return 0;
}
```

## CMakeLists

We need to create and edit a file, inside the TestSQL folder, named **CMakeLists.txt** like this: 

```
cmake_minimum_required(VERSION 3.0)

project(TestSQL)

find_package(SQLite3 REQUIRED)

include_directories(${SQLite3_INCLUDE_DIRS})
link_directories(${SQLite3_LIBRARY_DIR})
link_libraries(${SQLite3_LIBRARIES})

add_executable(testSQL ./sources/main.cpp )
```

Here we introduced few more functions:

- find_package: will find location of the library.
- link_directories: specify paths needed at link time.
- link_libraries: specify libraries needed at link time.

In the unfortunate event where find_package doesnt find the library, we could also manually insert the path values in the other functions (include_directories, link_directories, link_libraries).

## Run Cmake, Makefile, Build, Execute

In the terminal:

```
cmake -S . -B builds -G "Unix Makefiles"
cmake --build builds
./builds/testSQL
```

The output should be:

```
Connected to database
```

And that concludes our TestSQL tutorial example.

## Library Components

Some libraries are divided into many different components, like ***Boost*** or ***SFML***.

We can specify which components are needed into our code, like this:

```
find_package(SFML 
             COMPONENTS 
             graphics 
             window 
             system 
             audio 
             network 
             REQUIRED)
find_package(Boost COMPONENTS asio REQUIRED)
```

This piece of code above will find Boost asio component and all 5 SFML components: graphics, window, system, audio and network.

© Paul Caron, aka ChillPill
Cmake tutorial - linking libraries
