cmake的toolchain自定义变量失效问题

在编译我们库的时候，cmake执行到toolchain.cmake的时候，一些自定义变量是空的，但是看参数我是已经传递进去了

简介

toolchain

toolchain的用途官网解释的很清楚[1]，主要是为了交叉编译

• Cross-compiling

Cross-compiling a piece of software means that the software is built on one system, but is intended to run on a different system.

分析

测试用例

官网代码拿过来整一个简单的测试用例[2]

MESSAGE("------------------------------------------1" ${
   
   ANDROID_NDK})
if( NOT ANDROID_NDK )
  MESSAGE("111")
else()
  MESSAGE("222")
endif()
# the name of the target operating system
set(CMAKE_SYSTEM_NAME Linux)

# which C and C++ compiler to use
set(CMAKE_C_COMPILER /home/alex/eldk-mips/usr/bin/mips_4KC-gcc)
set(CMAKE_CXX_COMPILER
    /home/alex/eldk-mips/usr/bin/mips_4KC-g++)

# location of the target environment
set(CMAKE_FIND_ROOT_PATH /home/alex/eldk-mips/mips_4KC
                          /home/alex/eldk-mips-extra-install )

# adjust the default behavior of the FIND_XXX() commands:
# search for headers and libraries in the target environment,
# search for programs in the host environment
set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
MESSAGE("------------------------------------------2")

执行cmake命令，把自定义变量ANDROID_NDK传递过去

cmake -DANDROID_NDK=externals/android-ndk-r10e -DCMAKE_TOOLCHAIN_FILE=..\linux.toolchain.cmake ..

输出结果：

F:\study\compile\cmake\cmake_toolchain\build>cmake -DANDROID_NDK=externals/android-ndk-r10e -DCMAKE_TOOLCHAIN_FILE=..\linux.toolchain.cmake ..
-- Building for: Visual Studio 17 2022</