cmake的"add_custom_command"预处理头文件? [英] cmake 'add_custom_command' to pre-process header files?

问题描述

我正在从事需要cmake的项目.我想在我的makefile文件中添加一些自定义规则，但不能完全理解该怎么做.

i'm working on a project requiring cmake. i'd like to add some custom rules to my makefile, but can't quite get my head around how to do it.

c源文件和头文件都在同一目录中.在同一目录中也有许多 .def 文件，它们是编译过程中源文件中#include的某些头文件的源文件.

both c source files and header files are in the same directory. also in this same directory are a number of .def files, which are the sources for some of the header files #included in the source during compilation.

如果我要在Makefile中执行此操作，我会使用一条简单的规则，例如

if i were to do this in a makefile, i'd use a simple rule like

.SUFFIXES: .def

.def.h:
    $(PREPROC) $< > $@

我该如何用cmake做到这一点?

how can i do this with cmake ??

我尝试了以下各种排列，无论是否包含cmake工作目录规范:

i've tried various permutations of the following, both with and without cmake working directory specifications :

add_custom_command(
    OUTPUT vvr_const.h
    PRE_BUILD
    COMMAND preproc vvr_const.def > vvr_const.h
    DEPENDS vvr_const.def
)

add_custom_target(vvr_const.h DEPENDS vvr_const.def)

但是在编译c源文件时尚未生成头文件，因此编译失败.我还尝试了一种变体，其中我将上面的最后一行替换为

but the header file isn't generated by the time the c source file is compiled, so the compile fails. i've also tried a variation where i replace the last line above with

set_property(SOURCE main.c APPEND PROPERTY OBJECT_DEPENDS vvr_const.h)

在这种情况下，头文件是事先正确生成的，但是 make 无法找到它，并抱怨没有规则来创建目标 .h

in this case, the header file is correctly generated in advance, but make can't find it, and complains that there's no rule to make the target .h.

理想情况下，这将是一条通用规则，就像上面的 make 规则一样，但是如果出现以下情况，我不反对为每个 .def 文件制定单独的规则就是这样.

ideally this would be a general rule, like the make rule above, but i'm not opposed to making a separate rule for each of the .def files if that's what it takes.

欢呼.

推荐答案

您提出的 add_custom_command 方法有两个问题:

There are 2 problems with the add_custom_command approach you present:

1. 您未指定工作目录；默认情况下，该命令在构建目录中运行，而不在源目录中运行.
2. 您在这里依靠外壳程序功能(重定向到文件).即使这可能仍然有效.您应该采用不依赖于Shell的方法.

要解决问题1和2，我建议创建一个单独的cmake脚本文件，以接收输入和输出文件的绝对路径，并在custom命令中使用它们.这样，您就可以使用 execute_process 来指定要写入的文件，而无需依赖平台.

To solve issues 1 and 2 I recommend creating a seperate cmake script file receiving the absolute paths to input and output files and using those in the custom command. This allows you to use execute_process to specify the file to write without relying on the platform.

preprocess_def.cmake

# preprocess def file
# parameters INPUT_FILE and OUTPUT_FILE denote the file to use as source
# and the file to write the results to respectively

# use preproc tool to get data to write to the output file
execute_process(COMMAND preproc "${INPUT_FILE}"
                RESULT_VARIABLE _EXIT_CODE
                OUTPUT_FILE "${OUTPUT_FILE}")

if (_EXIT_CODE)
    message(FATAL_ERROR "An error occured when preprocessing the file ${INPUT_FILE}")
endif()

CMakeLists.txt

set(_INPUT_FILE "${CMAKE_CURRENT_SOURCE_DIR}/vvr_const.def")
set(_OUTPUT_FILE "${CMAKE_CURRENT_SOURCE_DIR}/vvr_const.h")

# not necessary to use build event here, if we mark the output file as generated
add_custom_command(OUTPUT "${_OUTPUT_FILE}"
    COMMAND "${CMAKE_BUILD_TOOL}" -D "OUPUT_FILE=${_OUTPUT_FILE}" -D "INPUT_FILE=${_INPUT_FILE}" -P "${CMAKE_CURRENT_SOURCE_DIR}/preprocess_def.cmake"
    DEPENDS "${_INPUT_FILE}")

add_executable(my_target vvr_const.h ...)
set_source_files_properties(vvr_const.h PROPERTIES GENERATED 1)

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