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CMake 基本使用方法--寫CMakeList.txt
https://techbase.kde.org/Development/Tutorials/CMake_(zh_CN)https://www.cmake.org/Wiki/CMake
這一章將從軟件開發者的角度來描述如何實用CMake。也就是說，如果你的目標是用CMake來管理你的生成過程，請閱讀這一章。
CMake的輸入
COMMAND(args)
這裏的 COMMAND 是命令行的名稱，args是用空格分割的參數列表。典型的，對與每一個項目的目錄存在一個CMakeLists.txt。 下麵我們將從一個簡單的Hello world例子開始介紹, 它的源代碼樹形文件包含這些文件：
Hello.c CMakeLists.txt
CMakeLists.txt將包含下麵兩行：
PROJECT（Hello)
ADD_EXECUTABLE(Hello Hello.c）
為了生成Hello的可執行程序，你隻需依照上麵CMake運行的過程描述來生成makefiles文件。 PROJECT 命令表明了產生的工作空間的名稱。 ADD_EXECUTABLE命令添加可執行的目標到生成程序。這個簡單的程序就隻需要這些設置。如歌你的項目需要一些文件才能編譯也很容易，隻想修改ADD_EXECUTABLE命令行如下：
ADD_EXECUTABLE（Hello Hello.c File2.c File3.c File4.c)
ADD_EXECUTABLE隻是很多CMake命令中的一種。比如更複雜的如下：
PROJECT(HELLO)
SET(HELLO_SRCS Hell.c File2.c File3.c)
IF(WIN32)
SET(HELLO_SRCS ${HELLO_SRCS} WinSupport.c)
ELSE (WIN32)
SET(HELLO_SRCS ${HELLO_SRCS} UnixSupport.c)
ENDIF (WIN32)
ADD_EXECUTABLE (Hello ${HELLO_SRCS})
#look for the Tcl library
FIND_LIBRARY(TCL_LIBRARY NAMES tcl tc184 tc183 tc 182 tc 180
PATHS /usr/lib /usr/local/lib)
IF (TCL_LIBRARY)
TARGET_ADD_LIBRARY (Hello TCL_LIBRARY)
ENDIF(TCL_LIBRARY)
在這個例子中 SET 命令用於將源文件組成一個列表。 IF 命令用於增加WinSupport.c或者UnixSupport.c到列表中。 最後 ADD_EXECUTABLE 命令用於 采用源文件列表HELLO_SRCS中列出的文件 生成可執行文件。FIND_LIBRARY命令用於尋找在一些指定目錄下的特定的Tcl庫文件。如果找到了，就將他們添加到Hello可執行程序的鏈接命令。 #行為注釋行。
CMake 是會定義一些使用的變量在CMakeList文件中。 比如，WIN32總是會在windows係統中被定義，而UNIX
總是在UNIX係統中被定義。
生成目標：（Build Targets)
SET()
SUBDIRS()
ADD_LIBRARY()
這裏生成靜態鏈接文件，例如ADD_LIBRARY(Whole ${HELLO_SRC}),就會生成一個libWhole.a可供鏈接
ADD_EXECUTABLE()
AUX_SOURCE_DIRECTORY()
PROJECT()
CMake會循環的查找從當前目錄到SUBDIRS列出的任何子目錄的文件。SET命令用於設定一個變量。ADD_LIBRARY將添加一個庫到目標之中。 ADD_EXECUTABLE添加一個可執行程序到目標列表中。（Note:編譯器執行的順序是先編譯源文件，然後生成庫文件，最後生成可執行文件）。AUX_SOURCE_DIRECTORY表示一個不在當前目錄的包含源文件的目錄。這些源代碼將插入當前的庫（LIBRARY）中。所有在AUX_SOURCE_DIRECTORY的文件將被編譯（如，*.c,*.cxx,*.cpp等等）。PROJECT（ProjectName）是一個用在MSVC中的特殊變量，用於為編譯器生成項目。他也為CMAKE定義連個有用的變量:ProjectName_SOURCE_DIR和ProjectName_BINARY_DIR.
編譯的標示和選項。除了上麵列出的命令外，CMakeLists.txt還包含如下的命令：
INCLUDE_DIRECTORIES()
LINK_DIRECTORIES()
LINK_LIBRARIES()
TARGET_LINK_LIBRARIES()
這些命令定義了用於編譯源代碼和生成可執行程序的目錄和庫。上麵列出的目錄的一個很重要的特性是它們會被任何子目錄繼承。也就是說，CMake依照目錄的分層結構來承襲這些命令。在每次遇到對這些命令的描述的時候都會被展開一次。比如說，如果在頂層的CMakeLists文件中有定義INCLUDE_DIRECTORIES(/usr/include)和SUBDIRS（./subdir1),並且在./subdir1/CMakeLists.txt有INCLUDE_DIRECTORIES(/tmp/foobar),於是最後網狀的結果是
INCLUDE_DIRECTORIES(/usr/include /tmp/foobar)
CMake會定義許多的模塊來查找通常會用到的包，比如OpenGL或Java。 這些模塊為你節省了很多的時間來編寫這些查找包。這些模塊可以像這樣加到你的CMakeList文件中，如下：
INCLUDE(${CMAKE_ROOT}/Modules/FindTCL.cmake)
CMAKE_ROOT 總是定義在CMake中，用於指向CMake安裝的路徑。查看Modules子目錄下的一些文件可以給你提供一些很好的idea關於怎樣用這些CMake命令。
給項目文件添加一個新的目錄
一個通用的方法來擴展一個項目文件是給他添加一個新的文件夾。這將包含三個步驟：
1.創建一個新的目錄在你的源代碼的分層目錄中
2.將這個新的目錄添加到SUBDIRS命令中
3.在這個新創建的目錄中用適當的命令建立一個CMakeLists.txt文件
This section describes how to use CMake from the software developer's point of view. That is, if your aim is to use CMake to manage your build process, read this section first.
Input to CMake
COMMAND(args)
Where COMMAND is the name of the command, and args is a white-space separated list of arguments to the command. (Arguments with embedded white-space should be quoted.) Typically there will be a CMakeLists.txt file for each directory of the project. Let's start with a simple example. Consider building hello world. You would have a source tree with the following files:
Hello.c CMakeLists.txt
The CMakeLists.txt file would contain two lines:
PROJECT (Hello)
ADD_EXECUTABLE(Hello Hello.c)
To build the Hello executable you just follow the process described in Running CMake above to generate the makefiles or Microsoft project files. The PROJECT command indicates what the name of the resulting workspace should be and the ADD_EXECUTABLE command adds an executable target to the build process. That's all there is to it for this simple example. If your project requires a few files it is also quite easy, just modify the ADD_EXECUTABLE line as shown below.
ADD_EXECUTABLE(Hello Hello.c File2.c File3.c File4.c)
ADD_EXECUTABLE is just one of many commands available in CMake. Consider the more complicated example below.
PROJECT (HELLO)
SET(HELLO_SRCS Hello.c File2.c File3.c)
IF (WIN32)
SET(HELLO_SRCS ${HELLO_SRCS} WinSupport.c)
ELSE (WIN32)
SET(HELLO_SRCS ${HELLO_SRCS} UnixSupport.c)
ENDIF (WIN32)
ADD_EXECUTABLE (Hello ${HELLO_SRCS})
# look for the Tcl library
FIND_LIBRARY(TCL_LIBRARY NAMES tcl tcl84 tcl83 tcl82 tcl80
PATHS /usr/lib /usr/local/lib)
IF (TCL_LIBRARY)
TARGET_ADD_LIBRARY (Hello TCL_LIBRARY)
ENDIF (TCL_LIBRARY)
In this example the SET command is used to group together source files into a list. The IF command is used to add either WinSupport.c or UnixSupport.c to this list. And finally the ADD_EXECUTABLE command is used to build the executable with the files listed in the source list HELLO_SRCS. The FIND_LIBRARY command looks for the Tcl library under a few different names and in a few different paths, and if it is found adds it to the link line for the Hello executable target. Note the use of the # character to denote a comment line.
CMake always defines some variables for use within CMakeList files. For example, WIN32 is always defined on windows systems and UNIX is always defined for UNIX systems. CMake defines a number of commands. A brief summary of the most commonly used commands follows here. Later in the document an exhaustive list of all pre-defined commands is presented. (You may also add your own commands, see the Extension Guide for more information.)
Build Targets:
SET()
SUBDIRS()
ADD_LIBRARY()
這裏生成靜態鏈接文件，例如ADD_LIBRARY(Whole ${HELLO_SRC})，就會生成一個libWhole.a，可供鏈接。
ADD_EXECUTABLE()
AUX_SOURCE_DIRECTORY()
PROJECT()
CMake works recursively, descending from the current directory into any subdirectories listed in the SUBDIRS command. The command SET is used for setting a variable, in this case to a list of source files. (Note: currently only C and C++ code can be compiled.) ADD_LIBRARY adds a library to the list of targets this makefile will produce. ADD_EXECUTABLE adds an executable to the list of targets this makefile will produce. (Note: source code is compiled first, then libraries are built, and then executables are created.) The AUX_SOURCE_DIRECTORY is a directory where other source code, not in this directory, whose object code is to be inserted into the current LIBRARY. All source files in the AUX_SOURCE_DIRECTORY are compiled (e.g. *.c, *.cxx, *.cpp, etc.). PROJECT (PojectName) is a special variable used in the MSVC to create the project for the compiler, it also defines two useful variables for CMAKE: ProjectName_SOURCE_DIR and ProjectName_BINARY_DIR.
Build flags and options. In addition to the commands listed above, CMakeLists.txt often contain the following commands:
INCLUDE_DIRECTORIES()
LINK_DIRECTORIES()
LINK_LIBRARIES()
TARGET_LINK_LIBRARIES()
These commands define directories and libraries used to compile source code and build executables. An important feature of the commands listed above is that are inherited by any subdirectories. That is, as CMake descends through a directory hierarchy (defined by SUBDIRS()) these commands are expanded each time a definition for a command is encountered. For example, if in the top-level CMakeLists file has INCLUDE_DIRECTORIES(/usr/include), with SUBDIRS(./subdir1), and the file ./subdir1/CMakeLists.txt has INCLUDE_DIRECTORIES(/tmp/foobar), then the net result is
INCLUDE_DIRECTORIES(/usr/include /tmp/foobar)
CMake comes with a number of modules that look for commonly used packages such as OpenGL or Java. These modules save you from having to write all the CMake code to find these packages yourself. Modules can be used by including them into your CMakeList file as shown below.
INCLUDE (${CMAKE_ROOT}/Modules/FindTCL.cmake)
CMAKE_ROOT is always defined in CMake and can be used to point to where CMake was installed. Looking through some of the files in the Modules subdirectory can provide good ideas on how to use some of the CMake commands.
Adding A New Directory to a project
A common way to extend a project is to add a new directory. This involves three steps:
Create the new directory somewhere in your source directory hierarchy.
Add the new directory to the SUBDIRS command in the parent directories CMakeLists.txt
Create a CMakeLists.txt in the new directory with the appropriate commands
最後更新：2017-04-03 08:26:21