Cmake selecting compilers and setting compiler options

One 、 Set the compiler version

Multiple versions of the compiler may be installed in the actual project platform , At the same time, different compilation parameters may need to be set for different functions , You can set the compiler version as follows

1、 Specify... Directly on the command line

cmake .. -DCMAKE_CXX_COMPILER=/usr/local/gcc/bin/g++

2、 Specified in the configuration file

set (CMAKE_C_COMPILER "/usr/local/gcc/bin/gcc")
set (CMAKE_CXX_COMPILER "/usr/local/gcc/bin/g++")

Modify global variables directly CMAKE_C_COMPILER and CMAKE_CXX_COMPILER Compiler path specified for . notes ： These two commands should be placed at the beginning of the file （cmake_minimum_required Under command , Above other commands ）, Otherwise it may not work .

CMAKE_C_COMPILER
It was originally to save environment variables "CC" Variable of value , and CC Is compiled C The preferred compiler for languages , But in the new CMP0054 If set in the policy CMAKE_C_COMPILER Will ignore CC Value .

CMAKE_CXX_COMPILER
And CMAKE_C_COMPILER similar , However, the environment variable corresponding to this variable is CXX, Is compiled C++ Compiler of language
Generated results

Two 、 Set compilation parameters

Suppose I use g++ compiler , add to "-std=c++11", “-Wall" and ”-Werror" Etc .

2.1 Use add_compile_options command

By means of CMakeLists.txt Add... To the file add_compile_options The command can be used to add parameters , Such as ：

add_compile_options(-std=c++11 -Wall -Werror)

But this command is for all types of compilers , In other words, the options added here will be used in all compilers , such as -std=c++11 Is aimed at C++ Compiler parameters for , It will also be used in C In the language compiler , Although it may not be wrong, it is not a good experience after all . And the parameters added by this command are recursive , That is, in a multi-layer directory structure , After setting options under the root file , All subdirectories will be compiled using .

2.2 By setting CMAKE_CXX_FLAGS To configure the

CMAKE_CXX_FLAGS Is aimed at C++ Compiler parameter options , Save environment variables by default CXX_FLAGS The content of , But if you modify the parameter value directly , Then the system will ignore the original CXX_FLAGS The content of . The setting method is as follows ：

set(CMAKE_CXX_FLAGS
    -std=c++11
    -Wall
    -Werror
)

This variable is only valid in the current file , If there are multiple modules in the project , Multiple compiled files , Then it needs to be in every CMakeLists.txt Add corresponding commands and parameters to the file .

The two ways are compared

Sum up , For some compilation options that are common throughout the project, you can use add_compile_options Command to add more convenient , For the individual options in each module, use CMAKE_CXX_FLAGS Better variables .

3、 ... and 、CMAKE__FLAGS Variable

What we use here CMAKE_CXX_FLAGS Variables are only for C++ Compiler options , For other programming languages , Just replace the part , At present cmake edition (3.17.2) The following languages are supported in ：

    CMAKE_C_FLAGS：C Language compiler options , Corresponds to the environment variable CFLAGS
    CMAKE_CXX_FLAGS：C++ Language compiler options , Corresponds to the environment variable CXXFLAGS
    CMAKE_CUDA_FLAGS：CUDA Language compiler options , Corresponds to the environment variable CUDAFLAGS
    CMAKE_Fortran_FLAGS：Fortran Language compiler options , Corresponds to the environment variable FFLAGS
 

Four 、 example

if (MSVC)
    # warning level 4 and all warnings as errors
    add_compile_options(/W4 /WX)
else()
    # lots of warnings and all warnings as errors
    add_compile_options(-Wall -Wextra -pedantic -Werror)
endif()

#  Determine compiler type , If it is gcc compiler , Add... To the compilation options c++11 Support 
if(CMAKE_COMPILER_IS_GNUCXX)
    set(CMAKE_CXX_FLAGS "-std=c++11 ${CMAKE_CXX_FLAGS}")
    message(STATUS "optional:-std=c++11")   
endif(CMAKE_COMPILER_IS_GNUCXX)

  Reference resources ：

CMake Advanced （ One ） Set compilation options _qinbo1234567890 The blog of -CSDN Blog _cmake Set compilation order

cmake(5)： Select compiler and set compiler options _ Xiangdi blog -CSDN Blog _cmake Set up compiler