让CMake声明目标虚假

问题描述

我想生成一些 compile 时间常数.对另一个问题的第一个答案使我非常接近.从我的CMakeLists.txt中:

I want to generate some compile time constants. The first answer to another question gets me quite close. From my CMakeLists.txt:

add_library(${PROJECT_NAME} STATIC ${CXX_SRCS} compile_time.hpp)
add_custom_command(OUTPUT compile_time.hpp
    COMMAND ${CMAKE_COMMAND} -P ${CMAKE_CURRENT_SOURCE_DIR}/compile_time.cmake)

从某种意义上来说，这是有效的，因为我第一次运行 make 时，它会生成 compile_time.hpp ，以便在我运行 make ，而不是 cmake .但是，当我重新运行 make 甚至是 cmake 重做makefile时， compile_time.hpp 并没有被重新制作.

This works in the sense that the first time I run make, it generates compile_time.hpp, so that the values of the variables are defined when I run make and not cmake. But compile_time.hpp is not remade when I rerun make or even cmake to redo the makefiles.

如何将目标 compile_time.cpp 标记为 phony ，以便始终重制目标?我尝试过

How can I make the target compile_time.cpp be marked as phony so that it is always remade? I tried

add_custom_target(compile_time.hpp)

无效.

推荐答案

add_custom_target 创建一个伪"目标:它没有输出，并且始终被构建.要使某些目标依赖于假"对象，请使用 add_dependencies()调用:

add_custom_target creates a "phony" target: It has no output and is always built. For make some target depended from the "phony" one, use add_dependencies() call:

add_custom_target(compile_time
    COMMAND ${CMAKE_COMMAND} -P ${CMAKE_CURRENT_SOURCE_DIR}/compile_time.cmake
)
# Because we use *target-level* dependency, there is no needs in specifying
# header file for 'add_library()' call.
add_library(${PROJECT_NAME} STATIC ${CXX_SRCS})
add_dependencies(${PROJECT_NAME} compile_time)

头文件扫描将自动检测到

头文件 compile_time.h 中库的依赖性.因为脚本 compile_time.cmake 无条件更新此标头，所以每次都将重建该库.

Library's dependency from the header compile_time.h will be detected automatically by headers scanning. Because script compile_time.cmake updates this header unconditionally, the library will be rebuilt every time.

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