Mastering CMake

chapters 1-2

• cmake-gui or ccmake (curses lib version) can be run to update configurations

chapter 3

generators

• global per project generator
• every folder has a local generator for creating Makefiles
• each in turn will create content based on CMakeLists

targets

• stored in cmMakefile; e.g. add_library, add_executable
• add_library (foo STATIC foo.c): foo can be used in the CML later
• can keep track of general properties w/ set_target_properties and get_target_property

commands

• generic set|get_property commands
• all variables defined have visibility in the following scope and well as in children of the current scope
  • we can explicitly set variables with PARENT_SCOPE if required: set (foo 1 PARENT_SCOPE)
• user selections and options are cached
  • we can explicitly define vars in the cache, but their type need to be specified: set (USE_JPEG ON CACHE BOOL "include jpeg?")

chapter 4

• project: if CXX enabled, C is included as well
• set / remove / separate_arguments - input a string containing multiple space separated values, outputs a list
• if can either have the condition specified everywhere - strings must remain the same - or all others can have just empty conditions
• possible operations in the check: NOT, AND, OR, DEFINED, MATCHES, EQUAL, LESS, STREQUAL, …, VERSION_GREATER

if (FOO)   
    # do something
else (FOO)     # or else ()
# elseif (BAR) is also supported
    # something else
endif (FOO)    # or endif ()

• foreach and while

  foreach (afile one two three)
    add_test(${afile}-test .... -D -V -A ...)
  endforeach (afile)
  

• macros are called similarly to functions, but its arguments are replaced prior to executing it
  • they can have also variable number of parameters
• we can specify minimum required version for cmake cmake_minimum_required (VERSION 2.8)
• cmake modules are components which can be reused - they are located in the Modules subfolder
  • include (moduleName) the full path to the module can as well be provided instead
• a policy (version dependent) can be set or queried, useful on cmake version upgrades
  • policies can be silenced w/ cmake_policy (SET CMPXXXX OLD) or enabled w/ ... NEW)
• system libraries can be targeted w/ the following snippet

  find_library (M_LIB m)
  target_link_libraries (my_executable ${M_LIB})
  

• shared libraries
  • entire unit is the atomic unit, this can cause issues when converting from static to shared library
  • the linking order needs to be taken into account, as linker do a single pass to search for symbols (pg 64)
  • ldd command to see which libraries are used by a binary
  • the linked libraries for different “.so” versions can be set by set_target_properties
• installing files
  • couple of signatures defined TARGETS, FILES, PROGRAMS, DIRECTORY, SCRIPT and CODE
  • a target is coming from add_executable or add_library; e.g. shared lib in /lib and static lib in project directory, same as binary
    • install (TARGETS myStaticLib DESTINATION lib/myproject)
  • general purpose files to be installed, such as header files, can be installed using the FILES signature
  • file permissions can be set using the FILE|DIRECTORY_PERMISSIONS directrives
• prerequisite shared libraries
  • GetPrerequisites.cmake module provides get_prerequisites function to analyze and classify the dependent libraries - it will produce a list of the shared libraries required
• imported and exported targets

chapter 5 - system inspection

• most used are find_path and find_library

  find_library (SOME_LIBRARY  NAMES somelib somelib2  PATHS /usr/local/lib /usr/lib)
  find_path    (SOME_INCLUDES       some.h                  /usr/local/include /usr/include)
  include_directories (${SOME_INCLUDES})
  add_executable ([...])
  target_link_libraries (myapp ${SOME_LIBRARY})
  

• all find commands will look in the $PATH variable; windows registry can be used as well
  • if cmake doesn’t find the files the value will be set to VAR-NOTFOUND, the value will evaluate as false in if statements
  • order is important, if you prefer somelib2 over somelib, you need to re-order them
  • you shouldn’t code against platform-specific but against feature-specific (ifdefs)
  • try_compile and try_run can be used to validate presence and implementation of specific libraries