Notes on cmake compilation tool

cmake

cmake On

What is? CMAKE

• CMake It's a cross platform compilation tool .
• First write CMakeLists.txt file , And then through cmake The order will CMakeLists.txt Files are converted into executable files of the corresponding platform make file , Last use make Command compile source code to generate executable program or library file , So as to avoid different platforms Makefile The problem of format .

C/C++ Compilation process

• The compilation process is actually a language （ It's usually a high-level language ） Translate into another language （ It's usually a low-level language ）. C/C++ The main process of program compilation ： Source code → The preprocessor → compiler → Assembler → The linker → Executable program .

• Preprocessing ： C/C++ in , Before the compiler compiles the source file , First, it should be pretreated .

  • The preprocessor provides a set of precompiled processing instructions and preprocessing operators , Formally # start , Actually, it doesn't belong to C/C++ The statement in , Cannot be translated by compiler , You need to do a preprocessing before the real compilation , Last output one “.i” file .

• compile ： Compiling is to put C/C++ Convert code to assembly code .

  • The compiler needs to pass lexical analysis and syntax analysis , After confirming that all instructions conform to the syntax rules and there are no syntax errors , Convert code into assembly language , Generate assembly code .

• assembly ： Assembly is the process of translating the assembly code output in the previous step into the target machine instructions , The generated object file is a machine language equivalent to the source program .

• link ： The link is the object file generated by the assembly 、 The target file of the system library 、 Linking library files , Generate executable programs that can run on a specific platform .

CMake Common variables

• CMAKE_BINARY_DIR、 PROJECT_BINARY_DIR、<projectname>_BINARY_DIR
  • These three variables refer to the same content , If it is in source compile , Refers to the project top-level directory ,
  • If it is out-of-source compile , It refers to the directory where project compilation occurs .
  • PROJECT_BINARY_DIR Slightly different from other instructions , Now? , You can understand that they are consistent .
• CMAKE_SOURCE_DIR、PROJECT_SOURCE_DIR、 <projectname>_SOURCE_DIR
  • These three variables refer to the same content , No matter how you compile it , It's all the top-level catalogue of the project .
  • stay in source Compile time , He followed CMAKE_BINARY_DIR And so on .
• CMAKE_CURRENT_SOURCE_DIR
  • Refers to the current processing of CMakeLists.txt Path , For example, we mentioned above src subdirectories .
• CMAKE_CURRRENT_BINARY_DIR
  • If it is in-source compile , It goes with CMAKE_CURRENT_SOURCE_DIR Agreement , If it is out-of-source compile , He means target Compile Directory .
  • Use the ADD_SUBDIRECTORY(src bin) You can change the value of this variable .
  • Use SET(EXECUTABLE_OUTPUT_PATH < New path >) It doesn't affect this variable , It only changes the path where the final target file is stored .
• CMAKE_MODULE_PATH
  • This variable is used to define its own cmake The path of the module .
  • Eg：SET(CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR}/cmake), And then you can go through INCLUDE Command to call your own module .
• EXECUTABLE_OUTPUT_PATH and LIBRARY_OUTPUT_PATH
  • They are used to redefine the storage directory of the final results , We mentioned these two variables earlier .

How to write cmake

• cmake_minimum_required(VERSION 3.16)： Is used to specify the cmake Minimum version requirements ;
  project(projectName) ： Used to specify the project name ;
  include_directories() ： Used to import header file search path ;
  aux_source_directory(src dir_srcs)： Used to include the source file directory ;
  set(TEST_MATH) ： Used to set environment variables , All the source files used for compilation should be put here ;
  add_executable(${PROJECT_NAME} ${TEST_MATH})： Used to add executable files to compile ;
  target_link_libraries(${PROJECT_NAME} m)： It is used to add the library required by the executable ;
  

• New variable , Store source files ：

  • set (SRC_LIST ./main.c ./func.c ./func1.c)

• Multiple source files in different directories

  • Add the search path of the specified header file
    • include_directories (func1 func2)
  • Search all source files in the specified path , And save it in the variable
    • aux_source_directory (func1 SRC_LIST1)

• Add a subdirectory to the current project where the source files are stored

  • add_subdirectory (src)

• Store the generated executable file in bin Under the table of contents

  • set (EXECUTABLE_OUTPUT_PATH ${PROJECT_SOURCE_DIR}/bin)

• Links to Libraries

  • Save the specified library file in the specified directory to the variable FUNC_LIB in
    • find_library(FUNC_LIB func HINTS ${PROJECT_SOURCE_DIR}/func/lib)
    • find_library: Find the specified library in the specified directory , And store the absolute path of the library in the variable , Parameter 1 is the variable name , The second parameter is the library name , The third parameter is HINTS, Parameter 4 is path .
    • Use find_library The advantage is to perform cmake .. Will find out whether the library exists , In this way, errors can be found in advance , Don't wait for the link .

Add compile options ：

• Sometimes you want to add some compilation options when compiling a program , Such as -Wall,-std=c++11 etc. , You can use add_compile_options To operate .
  • add_compile_options(-std=c++11 -Wall)
    • add to C++ 11 Standard support , And let the compiler warn the code as much as possible

Add control options

option command ： Parameters 1 by option Name , Parameters 2 For the string , describe option The function of , Parameters 3 by option Value ,ON or OFF, You can also leave it blank. The default is OFF.

First of all ：CMakeList Conditional compilation

• option(MYDEBUG "enable debug compilation" OFF)

  • if (MYDEBUG)
        add_executable(main2 main2.c)
    else()
        message(STATUS "Currently is not in debug mode")    
    endif()
    

• cmake .. -DMYDEBUG=ON command control

second ： Conditional compilation in code

• CMakeList Add

  • option(WWW1 "print one message" OFF)
    #  here `OFF、False`  `ON、True`  Fine 
    if (WWW1)
    	add_compile_options(-DWWW1)
    endif()
    

  • cmake China and Canada this , The purpose is to use this variable in the code

• *.h or *.cpp in Case study ：

  • #ifdef WWW1
        printf("--- define WWW1\n");
    #else
    	printf("---- not define WWW1\n");
    #endif
    

Cmake Advanced

//TODO