C++ Shared and Static Libraries

Often, we have a file like main.cpp calling functions from other files, which are called libraries. There are two types:

• Static libraries (.a)
• Shared libraries (.so)

A static library will generate a copy each time it’s called, the shared library only has one copy, which saves space.

In CMake:

// Static library
add_library( hello libHelloSLAM.cpp )
 
// Shared library
add_library( hello_shared SHARED libHelloSLAM.cpp)
 
// Link files
target_link_libraries( helloExecutable hello )

This add_library is needed whenever we are including .h files and these interface files have implementation files (.cpp). For existing libraries like Eigen Basics, add_library isn’t needed because it doesn’t have .cpp files, only .h.

Common CMake commands:

• cmake_minimum_required
• project
• include_directories
• add_library
• add_executable
• target_link_libraries

Using OpenCV with CMake:

cmake_minimum_required(VERSION 2.8)
project( DisplayImage )
find_package( OpenCV REQUIRED )
include_directories( ${OpenCV_INCLUDE_DIRS} )
add_executable( DisplayImage DisplayImage.cpp )
target_link_libraries( DisplayImage ${OpenCV_LIBS} )