CMake syntax - Environment Variable
1. Define environment variables
set(ENV{<variable>} [<value>])
- ENV: environment variable token prefix
- Variable: variable name
- Value: variable value
2. Application environment variables
2.1 code structure
- learn_cmake: is the root directory
- build: configure the output directory for CMake (in this case, where the sln solution is generated)
- cmake_config.bat: script to execute CMake configuration process (double click to run directly)
- CMakeLists.txt: CMake script
2.2 example code
-
Sample code (content of CMakeLists.txt file)
cmake_minimum_required(VERSION 3.18) # Set project name set(PROJECT_NAME KAIZEN) # Set project version number set(PROJECT_VERSION "1.0.0.10" CACHE STRING "Default version number") # Engineering definition project(${PROJECT_NAME} LANGUAGES CXX C VERSION ${PROJECT_VERSION} ) # Print start log message(STATUS "\n########## BEGIN_TEST_ENV_VARIABLE") # Judge Java_ Is the home variable defined if(DEFINED ENV{JAVA_HOME}) message("JAVA_HOME: $ENV{JAVA_HOME}") else() message("NOT DEFINED JAVA_HOME VARIABLES") endif() # Define environment variables set(ENV{CMAKE_PATH} "F:/cmake") # Judge cmake_ Is the path environment variable defined if(DEFINED ENV{CMAKE_PATH}) message("CMAKE_PATH_1: $ENV{CMAKE_PATH}") else() message("NOT DEFINED CMAKE_PATH VARIABLES") endif() # Define the test function and newly define the environment variable in the function function(test_env_variable) # Accessing the environment variable CMAKE_PATH message("CMAKE_PATH_2: $ENV{CMAKE_PATH}") # Define environment variables within functions set(ENV{CMAKE_FUNC} "F:/cmake/dir") # Judge cmake_ Is the func environment variable defined if(DEFINED ENV{CMAKE_FUNC}) message("CMAKE_FUNC_1: $ENV{CMAKE_FUNC}") else() message("NOT DEFINED CMAKE_FUNC_1 VARIABLES") endif() endfunction() # Call function test_env_variable() # Judge cmake_ Is the func environment variable defined if(DEFINED ENV{CMAKE_FUNC}) message("CMAKE_FUNC_2: $ENV{CMAKE_FUNC}") else() message("NOT DEFINED CMAKE_FUNC_2 VARIABLES") endif() # If there is no parameter value set(ENV{CMAKE_FUNC}) # Judge cmake_ Is the func environment variable defined if(DEFINED ENV{CMAKE_FUNC}) message("CMAKE_FUNC_3: $ENV{CMAKE_FUNC}") else() message("NOT DEFINED CMAKE_FUNC_3 VARIABLES") endif() # Define the test macro and newly define the environment variable in the function macro(test_env_var) # Accessing the environment variable CMAKE_PATH message("CMAKE_PATH_3: $ENV{CMAKE_PATH}") # Defining environment variables within macros set(ENV{CMAKE_MACRO} "F:/cmake/macro") # Judge cmake_ Is macro environment variable defined if(DEFINED ENV{CMAKE_MACRO}) message("CMAKE_MACRO_1: $ENV{CMAKE_MACRO}") else() message("NOT DEFINED CMAKE_MACRO_1 VARIABLES") endif() endmacro() # Call macro test_env_var() # Judge cmake_ Is macro environment variable defined if(DEFINED ENV{CMAKE_MACRO}) message("CMAKE_MACRO_2: $ENV{CMAKE_MACRO}") else() message("NOT DEFINED CMAKE_MACRO_2 VARIABLES") endif() # If more than one parameter value set(ENV{CMAKE_FILE} "F:/cmake/cmake1.txt" "F:/cmake/cmake2.txt") # Judge cmake_ Is the file environment variable defined if(DEFINED ENV{CMAKE_FILE}) message("CMAKE_FILE: $ENV{CMAKE_FILE}") else() message("NOT DEFINED CMAKE_FILE VARIABLES") endif() # Print end log message(STATUS "########## END_TEST_ENV_VARIABLE\n") -
cmake_config.bat
@echo off set currentDir=%~dp0 set buildDir=%currentDir% set cmakeOutputDir=%currentDir%\build cmake -S %buildDir% -B %cmakeOutputDir% -G"Visual Studio 16 2019" -T v140 -A x64 pause
2.3 operation results
-
Local environment
Local installation VS version: Visual Studio 2019 (2015 toolset)
CMake version: 3.18.2
F:\learn_cmake λ cmake --version cmake version 3.18.2 CMake suite maintained and supported by Kitware (kitware.com/cmake).
-
Output results
-- Selecting Windows SDK version 10.0.18362.0 to target Windows 10.0.17763. -- The CXX compiler identification is MSVC 19.0.24245.0 -- The C compiler identification is MSVC 19.0.24245.0 -- Detecting CXX compiler ABI info -- Detecting CXX compiler ABI info - done -- Check for working CXX compiler: C:/Program Files (x86)/Microsoft Visual Studio 14.0/VC/bin/amd64/cl.exe - skipped -- Detecting CXX compile features -- Detecting CXX compile features - done -- Detecting C compiler ABI info -- Detecting C compiler ABI info - done -- Check for working C compiler: C:/Program Files (x86)/Microsoft Visual Studio 14.0/VC/bin/amd64/cl.exe - skipped -- Detecting C compile features -- Detecting C compile features - done -- ########## BEGIN_TEST_ENV_VARIABLE JAVA_HOME: C:\Program Files\Java\jdk1.8.0_201 CMAKE_PATH_1: F:/cmake CMAKE_PATH_2: F:/cmake CMAKE_FUNC_1: F:/cmake/dir CMAKE_FUNC_2: F:/cmake/dir NOT DEFINED CMAKE_FUNC_3 VARIABLES CMAKE_PATH_3: F:/cmake CMAKE_MACRO_1: F:/cmake/macro CMAKE_MACRO_2: F:/cmake/macro CMake Warning (dev) at CMakeLists.txt:98 (set): Only the first value argument is used when setting an environment variable. Argument 'F:/cmake/cmake2.txt' and later are unused. This warning is for project developers. Use -Wno-dev to suppress it. CMAKE_FILE: F:/cmake/cmake1.txt -- ########## END_TEST_ENV_VARIABLE -- Configuring done -- Generating done -- Build files have been written to: F:/learn_cmake/build Please press any key to continue. . .
3 Summary
-
When setting or reading environment variables, environment variables are accessed through ENV prefix.
-
When reading the value of environment variable, add the $sign before ENV; However, if does not need to add the $symbol when judging whether it is defined or not.
-
Set the environment variable. This command only affects the current CMake process, does not affect the process calling CMake, and does not affect the entire system environment.
-
When setting the environment variable, no value is assigned to the variable:
If there is an environment variable with the same name, this command will clear the existing environment variable with the same name;
If there is no environment variable with the same name, this command will be regarded as invalid code.
As in line 62 of the sample program, the existing environment variable cmake will be cleared_ Func, which results in line 21 of the output result: NOT DEFINED CMAKE_FUNC_3 VARIABLES
-
When setting environment variables, there is only one variable value. Redundant values are ignored and a warning message is prompted.
As shown in line 98 of the example program, the variable value is 2, the second value of the result is ignored, and CMake Warning will be printed into the output result.
-
Environment variable, there is no scope distinction. That is, functions, macros, subdirectories and included modules are the same, which will only affect the current CMake process.
For example, in lines 52 and 88 of the example program, after the test of calling functions and macros, the external environment variables can be accessed internally; Environment variables defined internally can also be used externally.
Subdirectories and functions belong to the same category (with scope distinction), and macros and containing modules belong to the same category (without scope distinction). Therefore, only two tests can explain the problem here.