CMake Lesson 1 - Targets, Install Directories, and Aliases

Important Variables

CMAKE_CURRENT_SOURCE_DIR

Directory containing the current CMakeLists.txt.

Example:

${CMAKE_CURRENT_SOURCE_DIR}/include

If the project is

calcpack/
├── CMakeLists.txt
├── include/
└── src/

then

${CMAKE_CURRENT_SOURCE_DIR}
/path/to/calcpack

Unlike CMAKE_SOURCE_DIR, this changes when entering subdirectories with add_subdirectory().

---

GNUInstallDirs

include(GNUInstallDirs)

Provides standard installation directories in a portable way.

Variable	Typical Value	Purpose
CMAKE_INSTALL_BINDIR	bin	Executables
CMAKE_INSTALL_INCLUDEDIR	include	Header files
CMAKE_INSTALL_LIBDIR	lib (sometimes lib64)	Libraries

Example:

install(
    TARGETS calcapp
    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
)

becomes

install/
└── bin/
    └── calcapp

Why use these variables?

Instead of

DESTINATION lib

use

DESTINATION ${CMAKE_INSTALL_LIBDIR}

Benefits:

• Portable across Linux, macOS, and Windows
• Supports distributions using lib64 or custom library paths
• Modern CMake best practice

---

Library Target

add_library(calcpack src/calc.cpp)

Creates a target named:

calcpack

Link it with:

target_link_libraries(app PRIVATE calcpack)

---

Target Alias

add_library(calcpack::calcpack ALIAS calcpack)

Creates a second name for the same target.

Both are equivalent:

target_link_libraries(app PRIVATE calcpack)

target_link_libraries(app PRIVATE calcpack::calcpack)

The :: is a convention indicating a namespaced CMake target.

Examples:

fmt::fmt
Qt6::Core
Boost::filesystem
OpenSSL::SSL
calcpack::calcpack

Benefits:

• Clearer code
• Matches imported libraries from find_package()
• Consistent names before and after installation

---

Key Takeaways

• CMAKE_CURRENT_SOURCE_DIR → current source directory.
• CMAKE_INSTALL_*DIR → standard installation locations.
• GNUInstallDirs works on Linux, macOS, and Windows.
• add_library(... ALIAS ...) creates another name for the same target.
• Prefer namespaced targets (project::library) in modern CMake.