During the call to cmake it is possible to create files that use variables from the CMakeLists.txt and cmake cache. During CMake generation the file is copied to a new location and any cmake variables are replaced.
Configure Files Generation - 使用配置文件的代码生成
Table of Contents
Introduction - 简介
在CMake的调用过程中可能会使用CMakeList.txt和CMake缓存中的变量来创建文件；在CMake的生成过程中，该文件会被复制到新的位置，其中所有的变量将被使用他们的值替换。
本教程的目录结构如下所示：
The files in this tutorial are below:
$ tree
.
├── CMakeLists.txt
├── main.cpp
├── path.h.in
├── ver.h.in-
CMakeLists.txt - 描述你希望能够运行的CMake命令
-
CMakeLists.txt - Contains the CMake commands you wish to run
-
-
main.cpp - 包含主函数的源文件
-
main.cpp - The source file with main
-
-
path.h.in - 描述待构建目录的文件
-
path.h.in - File to contain a path to the build directory
-
-
ver.h.in - 描述工程版本信息的文件
-
ver.h.in - File to contain the version of the project
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Concepts - 概念
Configure Files - 配置文件
在CMake中，你可以在文件中使用 configure_file() 函数进行变量的替换，这一函数的必要参数是源文件和目标文件。
To do variable substitution in a file you can use the `configure_file()` function in CMake. This core arguments for this function are source file and destination file.
configure_file(ver.h.in ${PROJECT_BINARY_DIR}/ver.h)
configure_file(path.h.in ${PROJECT_BINARY_DIR}/path.h @ONLY)第一个例子，在ver.h.in文件中，CMake可以将使用 ${} 或 @@ 的语法来定义一个CMake变量。在执行代码生成之后，在 PROJECT_BINARY_DIR 目录下将会出现一个新的ver.h文件。
The first example above, allows the variable to be defined like a CMake variables using
the `${}` syntax or an `@@` in the ver.h.in file. After generation a new file ver.h will be available
in the `PROJECT_BINARY_DIR`.
const char* ver = "${cf_example_VERSION}";第二个例子，在path.h.in文件中，@ONLY 指定了它只能用 @@ 的语法来定义一个CMake变量。同样地，在执行代码生成之后，在 PROJECT_BINARY_DIR 目录下将会出现一个新的path.h文件。
The second example, only allows variables to be defined using the `@@` syntax in the path.h.in file. After generation a new file path.h will be available in the `PROJECT_BINARY_DIR`.
const char* path = "@CMAKE_SOURCE_DIR@";构建示例
$ mkdir build
$ cd build/
$ cmake ..
-- The C compiler identification is GNU 4.8.4
-- The CXX compiler identification is GNU 4.8.4
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- 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
-- Configuring done
-- Generating done
-- Build files have been written to: /home/matrim/workspace/cmake-examples/03-code-generation/configure-files/build
$ ls
CMakeCache.txt CMakeFiles cmake_install.cmake Makefile path.h ver.h
$ cat path.h
#ifndef __PATH_H__
#define __PATH_H__
// version variable that will be substituted by cmake
// This shows an example using the @ variable type
const char* path = "/home/matrim/workspace/cmake-examples/03-code-generation/configure-files";
#endif
$ cat ver.h
#ifndef __VER_H__
#define __VER_H__
// version variable that will be substituted by cmake
// This shows an example using the $ variable type
const char* ver = "0.2.1";
#endif
$ make
Scanning dependencies of target cf_example
[100%] Building CXX object CMakeFiles/cf_example.dir/main.cpp.o
Linking CXX executable cf_example
[100%] Built target cf_example
$ ./cf_example
Hello Version 0.2.1!
Path is /home/matrim/workspace/cmake-examples/03-code-generation/configure-files