Print out all accessible variables

get_cmake_property(_variableNames VARIABLES)
list (SORT _variableNames)
foreach (_variableName ${_variableNames})
    message(STATUS "${_variableName}=${${_variableName}}")
endforeach()

execute shell in CMAKE and get the output of it

execute_process(COMMAND sdl2-config --cflags OUTPUT_VARIABLE CFLAGS_OF_SDL)   

The output of 'sdl2-config --cflags' is stored in the variable CFLAGS_OF_SDL.

Get the external project's file in the cmake

FetchContent_Declare(imgui                                           
   URL https://github.com/ocornut/imgui/archive/refs/tags/v1.89.3.zip
   DOWNLOAD_DIR ${CMAKE_CURRENT_SOURCE_DIR}/imgui                    
)                                                                    
FetchContent_Populate(imgui)                                         

Get the external project without build in the cmake

# Get imgui v1.89.3                                                 
ExternalProject_Add(imgui                                           
  URL https://github.com/ocornut/imgui/archive/refs/tags/v1.89.3.zip
  TIMEOUT 600                                                       
  SOURCE_DIR ${IMGUI_DIR}                                           
      CONFIGURE_COMMAND ""                                          
    BUILD_COMMAND ""                                                
    INSTALL_COMMAND ""                                              
                                                                    
)                                                                   

The file v1.89.3.zip is extracted in the SOURCE_DIR. But the project is not build. This tip is used in using a imgui, sqlite project that is provided only source/header files.

Print out timestamp & calculate elapse time

string(TIMESTAMP TODAY "%Y%m%d %I %M %S") 
MESSAGE("Time stamp [${TODAY}]")

string(TIMESTAMP START_P "%s")
...
... do something
...
string(TIMESTAMP END_P "%s")
MATH(EXPR ELAPSE "${END_P} - ${START_P}")
MESSAGE ( "CHK [${ELAPSE}]")