Package vs Library

Imagine you want to use zlib in your project, you need to find the header file zlib.h, and the library libz.so (on Linux). You can use the low-level cmake commands find_path and find_library to find them, or you can use find_package(ZLIB). The later command will try to find out all what is necessary to use zlib. It can be extra macro definitions, or dependencies.

Update, more detail about find_package: when the CMake command find_package(SomeThing) is called, as in the documentation, there are two possible modes that cmake can run:

• the module mode (that searches for a file FindSomeThing.cmake)
• or the config mode (that searches for a file named SomeThingConfig.cmake)

For ZLIB, there is a module named FindZLIB, shipped with CMake itself (on my Linux machine that is the file /usr/share/cmake/Modules/FindZLIB.cmake). That module is a CMake script that uses the CMake API to search for ZLIB files in default locations, or ask the user for the location if it cannot be found automatically.