目录
添加一个option!
添加一个option!
option，正如其意，就是选项的意思。我们这里需要演示一下option的做法。
option对于大型的工程必然是非常常见的：一些模块会被要求编译，另一些客户不准备需要这些模块。option就是将这种需求组织起来，让脚本构建者有了清晰的逻辑组成的抓手。
举个最最简单的例子。我们打算写一个模块，这个模块其实就是根据用户静态的选择打印不同的话：
impl.c
void implA();
void implB();
void impl()
{
#ifdef USE_SPECIAL_IMPL
implB();
#else
implA();
#endif
}
impl(A/B).c
// implA.c
#include <stdio.h>
void implA()
{
printf("The Implement function is using Implements A");
}
// implB.c
#include <stdio.h>
void implB()
{
printf("The Implement function is using Implements B");
printf("\n which is surprised :)");
}
他们都在optional_implements文件夹中：
➜ tree -L 2 . ├── build | ├─ ... # Ommited ├── CMakeLists.txt ├── Config.h.in ├── main.c ├── MathLibs │ ├── CMakeLists.txt │ ├── mathLibs.c │ └── mathLibs.h └── optional_implements ├── implA.c ├── implB.c └── impl.c
下面就是在cmake中体现出来了,我们使用的就是option这个命令：
option(USE_SPECIAL_IMPL "the special implements of impl function" ON)
option这个命令的格式非常简单：就是目标控制变量 + 描述 + 默认定义。这里的ON表达是开启的意思。OFF就是关闭:
cmake .. -DUSE_SPECIAL_IMPL=OFF
cmake当中就是就是采用D + 控制变量名称=ON/OFF来决定的。
更好的办法是使用cmake-gui来进行可视化的构建：
我们继续实现这个根据option来决定编译行为不一致的实现。很简单，我们只需要控制：
if (USE_SPECIAL_IMPL)
set(CharliesDemoSrc ${CharliesDemoSrc} optional_implements/implB.c)
else()
set(CharliesDemoSrc ${CharliesDemoSrc} optional_implements/implA.c)
endif()
add_executable(CharliesDemo ${CharliesDemoSrc})
if (USE_SPECIAL_IMPL)
target_compile_definitions(CharliesDemo PRIVATE "USE_SPECIAL_IMPL")
endif()
下面给出现在CMakeLists.txt脚本的全貌：
cmake_minimum_required(VERSION 3.30)
project(CharliesDemo
VERSION 1.0)
set(CharlieConstVar 1)
set(CharlieConstDouble 1.1)
configure_file(Config.h.in Config.h)
add_subdirectory(MathLibs)
set(CharliesDemoSrc main.c optional_implements/impl.c)
option(USE_SPECIAL_IMPL "the special implements of impl function" ON)
if (USE_SPECIAL_IMPL)
set(CharliesDemoSrc ${CharliesDemoSrc} optional_implements/implB.c)
else()
set(CharliesDemoSrc ${CharliesDemoSrc} optional_implements/implA.c)
endif()
add_executable(CharliesDemo ${CharliesDemoSrc})
if (USE_SPECIAL_IMPL)
target_compile_definitions(CharliesDemo PRIVATE "USE_SPECIAL_IMPL")
endif()
target_include_directories( CharliesDemo PUBLIC
"${PROJECT_BINARY_DIR}"
"${PROJECT_SOURCE_DIR}/MathLibs")
target_link_libraries(CharliesDemo PUBLIC MathLib)
看官自行尝试cmake的使用
➜ cd build && cmake .. -DUSE_SPECIAL_IMPL=OFF && make -- Configuring done (0.0s) -- Generating done (0.0s) -- Build files have been written to: /home/Charliechen/Works/cmake_learning/build [ 16%] Building C object MathLibs/CMakeFiles/MathLib.dir/mathLibs.c.o [ 33%] Linking C static library libMathLib.a [ 33%] Built target MathLib [ 50%] Building C object CMakeFiles/CharliesDemo.dir/main.c.o [ 66%] Building C object CMakeFiles/CharliesDemo.dir/optional_implements/impl.c.o [ 83%] Building C object CMakeFiles/CharliesDemo.dir/optional_implements/implA.c.o [100%] Linking C executable CharliesDemo [100%] Built target CharliesDemo
➜ ./CharliesDemo VERISON_MAJOR: 11 + 2 = 3The Implement function is using Implements A⏎
➜ cd build && cmake .. -DUSE_SPECIAL_IMPL=ON && make -- Configuring done (0.0s) -- Generating done (0.0s) -- Build files have been written to: /home/Charliechen/Works/cmake_learning/build [ 33%] Built target MathLib [ 50%] Building C object CMakeFiles/CharliesDemo.dir/main.c.o [ 66%] Building C object CMakeFiles/CharliesDemo.dir/optional_implements/impl.c.o [ 83%] Building C object CMakeFiles/CharliesDemo.dir/optional_implements/implB.c.o [100%] Linking C executable CharliesDemo [100%] Built target CharliesDemo
VERISON_MAJOR: 11 + 2 = 3The Implement function is using Implements B which is surprised :)⏎
