c++ - 带有未知输出文件的 CMake ADD_CUSTOM_COMMAND

Question

我有一个工具可以生成一些 cpp 和头文件，并想用 ADD_CUSTOM_COMMAND 添加它在构建期间自动执行它并将文件添加到项目中。问题是(大部分)输出文件的名称事先不知道。我如何添加这些文件？

Answer 1

简介
我假设您的目标不是使用 ADD_CUSTOM_COMMAND ，而是:

cmake 识别您生成的文件依赖于生成脚本 .这意味着:当你的生成脚本发生变化时，当你执行 cmake --build 时，文件会自动重新生成不同的文件名。下一次。

cmake 识别出您的可执行文件/库依赖于生成的文件，一旦这些文件重新生成，其文件名就会更改 .这意味着:由于 cmake --build 的相同调用，您的可执行文件/库被重建并使用重新生成的文件。

主要问题是文件名必须在 configuration time 处知道。 ，以便在 build time 处知道依赖关系.这意味着您需要将文件的生成移动到 configuration时间。
您要么需要获取文件名作为生成脚本的输出，要么使用文件通配符。通常我这样做 不推荐 的用法文件通配 ，因为它在适当的依赖关系方面有一些缺点。在您的情况下，通配符增加了实际值(value)，但必须弥补劣势。
下面我编译了一个完整的示例项目，它展示了它是如何工作的。我不是说这是标准的做法，但我认为它很好地满足了要求。
示例设置
我创建了一个最小设置，使所有这些工作:

myProject
|- CMakeLists.txt
|- main.cpp
|- myClass.h
|- generate.sh

myClass.h

#ifndef MY_CLASS_H
#define MY_CLASS_H
int do_something_a();
int do_something_b();
#endif // MY_CLASS_H

main.cpp

#include "myClass.h"
#include <iostream>

int main(const int argc, const char **argv)
{
  int a = do_something_a();
  int b = do_something_b();
    
  std::cout << "A:" << a << ", B:" << b << std::endl;

  return 0;
}

generate.sh
只需创建 2 个 cpp 文件来实现 do_something_a()和 do_something_b() .生成的文件名包含一个随机数，也由 do_something_*() 返回。功能。文件被放入子目录 generated .

#!/usr/bin/env bash

# just creating a new subfolder; remove its contents if already existing
dir1="generated"
if [ ! -d ${dir1} ]; then mkdir ${dir1}; fi
rm -rf ${dir1}/*

# just create a cpp file with random name and implement do_something_a()    
var1=`date +%N`
file1=${dir1}/myClass.${var1}.cpp
echo '#include "myClass.h"' > ${file1}
echo 'int do_something_a() { return '${var1}'; }' >> ${file1}

# just create a cpp file with random name and implement do_something_b()
var2=`date +%N`
file2=${dir1}/myClass.${var2}.cpp
echo '#include "myClass.h"' > ${file2}
echo 'int do_something_b() { return '${var2}'; }' >> ${file2}

CMakeLists.txt

cmake_minimum_required (VERSION 3.10.2)

project(useGenerateSourcesAtBuildStepProj
  VERSION 0.0.0.1
  DESCRIPTION "Minimum Example: Use Generated Files as dependency"
  LANGUAGES CXX
)

# just needed to force re-configuration, if generate.sh has changed.
# that's the tweak to overcome glob disadvantage
configure_file(
  ${CMAKE_CURRENT_SOURCE_DIR}/generate.sh
  ${CMAKE_CURRENT_BINARY_DIR}/generate.sh
)

# regeneration command executed at configuration time
# note: cannot call ${CMAKE_CURRENT_BINARY_DIR}/generate.sh, because not yet existing
execute_process(
  COMMAND bash ${CMAKE_CURRENT_SOURCE_DIR}/generate.sh
  WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
)

# globbing all generated files in sub directory `generated` at configuration time after execute_process
FILE(GLOB GENERATED_SRC_FILES ${CMAKE_CURRENT_BINARY_DIR}/generated/*)

# use generated files to build your executable
add_executable(useGenerateSourcesAtBuildStep main.cpp ${GENERATED_SRC_FILES})
target_include_directories(useGenerateSourcesAtBuildStep PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})

build
配置:

../bin/Release$ cmake -G"Unix Makefiles" ../..

输出:

-- The CXX compiler identification is GNU 7.5.0
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done    
-- Configuring done
-- Generating done
-- Build files have been written to: <dir>/bin/Release

内部版本:

../bin/Release$ make

输出:

Scanning dependencies of target useGenerateSourcesAtBuildStep
[ 25%] Building CXX object CMakeFiles/useGenerateSourcesAtBuildStep.dir/main.cpp.o
[ 50%] Building CXX object CMakeFiles/useGenerateSourcesAtBuildStep.dir/generated/myClass.488106246.cpp.o
[ 75%] Building CXX object CMakeFiles/useGenerateSourcesAtBuildStep.dir/generated/myClass.490335510.cpp.o
[100%] Linking CXX executable useGenerateSourcesAtBuildStep
[100%] Built target useGenerateSourcesAtBuildStep

生成的文件:

|- bin
    |- Release
        |- src
            |- generate.sh (due to configure_file)
            |- generated (directory containing all generated files)
            |   |- myClass.488106246.cpp
            |   |- myClass.490335510.cpp
            |- useGenerateSourcesAtBuildStep (your exectuable)

更改 generate.sh 并使用 make 重建:

../bin/Release$ make

输出:
您可以看到配置步骤再次完成并且生成的文件更改了它们的名称，但在将它们全部链接到您的可执行文件之前重建:

-- Configuring done
-- Generating done
-- Build files have been written to: /home/tangoal/Documents/data/300_Projects/_software/CPP/lib/test/bin/Release
Scanning dependencies of target useGenerateSourcesAtBuildStep
[ 25%] Building CXX object CMakeFiles/useGenerateSourcesAtBuildStep.dir/generated/myClass.565834060.cpp.o
[ 50%] Building CXX object CMakeFiles/useGenerateSourcesAtBuildStep.dir/generated/myClass.567160574.cpp.o

[ 75%] Linking CXX executable useGenerateSourcesAtBuildStep
[100%] Built target useGenerateSourcesAtBuildStep

执行程序:

../Release/src$ ./useGenerateSourcesAtBuildStep

输出:

A:565834060, B:567160574