---
title: CMake项目添加预编译头
date: 2017-12-28 11:46:13 +08:00
tags: [cmake, visual studio]
images: ["apple-touch-icon.png"]
categories: cmake
---

本文主要记录为CMake项目添加预编译头支持，以及过程中遇到的坑，比如`set_target_properties`连续调用两次失效的问题。

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各个编译器支持预编译头指令不同，这里仅以Visual Studio为例进行说明。

## 操作步骤

- 创建cmake宏文件`PrecompiledHeader.cmake`

```cmake PrecompiledHeader.cmake
#-------------------------------------------------------
# Support macro to use a precompiled header
# Usage:
#   use_precompiled_header(TARGET HEADER_FILE SRC_FILE)
#-------------------------------------------------------

macro(use_precompiled_header TARGET HEADER_FILE SRC_FILE)
  get_filename_component(HEADER ${HEADER_FILE} NAME)

  # Use MSVC_IDE to exclude NMake from using PCHs
  if (MSVC AND NOT NMAKE AND NOT OGRE_UNITY_BUILD)

    set_property(TARGET ${TARGET} APPEND_STRING PROPERTY
      COMPILE_FLAGS " /Yu\"${HEADER}\"")
    set_property(TARGET ${TARGET} APPEND_STRING PROPERTY
      COMPILE_FLAGS " /FI\"${HEADER}\"")
    set_source_files_properties(${SRC_FILE}
      PPROPERTIES COMPILE_FLAGS /Yc"${HEADER}")
  elseif (CMAKE_COMPILER_IS_GNUCXX OR CMAKE_COMPILER_IS_CLANGXX)
  endif ()
endmacro(use_precompiled_header)
```

- 在主工程的`CMakeLists.txt`中添加依赖

```cmake
list(APPEND CMAKE_MODULE_PATH ${CMAKE_SOURCE_DIR}/Tools/CMake)
include(PrecompiledHeader)
```

- 在需要使用预编译头的项目中调用`use_precompiled_header`宏函数

```cmake
use_precompiled_header(${PROJECT_NAME}
    "${CMAKE_CURRENT_SOURCE_DIR}/stdafx.h"
    "${CMAKE_CURRENT_SOURCE_DIR}/stdafx.cpp")
```

## 踩坑记录

- set_target_properties连续调用两次，导致前一次调用无效

在`PrecompiledHeader.cmake`文件中，最开始使用了如下的代码

{% note danger %}

{% codeblock lang:cmake %}
if (MSVC AND NOT NMAKE AND NOT OGRE_UNITY_BUILD)
    set_target_properties(${TARGET} PROPERTIES COMPILE_FLAGS /Yu"${HEADER}")
    set_target_properties(${TARGET} PROPERTIES COMPILE_FLAGS /FI"${HEADER}")
    set_source_files_properties(${SRC_FILE}
      PPROPERTIES COMPILE_FLAGS /Yc"${HEADER}"
    )
{% endcodeblock %}

{% endnote %}

可是发现永远只有/FI生效，后来查找了大量资料，替换为了`set_property APPEND`的形式，才最终解决。