Step5:系統檢測機制

如果系統有log和exp，我們在mysqrt方法中使用它們。在MathFunctions/CMakeLists.txt中，首先檢測它們是否存在，使用的語法是CheckSymbolExits。如果log和exp沒有被發現，需要m庫。

include(CheckSymbolExists) check_symbol_exists(log "math.h" HAVE_LOG) check_symbol_exists(exp "math.h" HAVE_EXP) if(NOT (HAVE_LOG AND HAVE_EXP))unset(HAVE_LOG CACHE)unset(HAVE_EXP CACHE)set(CMAKE_REQUIRED_LIBRARIES "m")check_symbol_exists(log "math.h" HAVE_LOG)check_symbol_exists(exp "math.h" HAVE_EXP)if(HAVE_LOG AND HAVE_EXP)target_link_libraries(MathFunctions PRIVATE m)endif() endif()

如果存在，使用?target_compile_definitions()?來指定?HAVE_LOG?and?HAVE_EXP?as?PRIVATE?的編譯定義.

if(HAVE_LOG AND HAVE_EXP)target_compile_definitions(MathFunctionsPRIVATE "HAVE_LOG" "HAVE_EXP") endif()

命令解釋：

target_compile_definitions(<target><INTERFACE|PUBLIC|PRIVATE> [items1...][<INTERFACE|PUBLIC|PRIVATE> [items2...] ...])

The?INTERFACE,?PUBLIC?and?PRIVATE?的關鍵字指定了下面參數的作用域。PRIVATE?and?PUBLIC?items will populate the?COMPILE_DEFINITIONS?property of?<target>.?PUBLIC?and?INTERFACE?items will populate the?INTERFACE_COMPILE_DEFINITIONS?property of?<target>. The following arguments specify compile definitions. Repeated calls for the same?<target>?append items in the order called.

COMPLIE_DEFINITIONS:編譯定義

?

在mysqrt方法中，可以使用：

#if defined(HAVE_LOG) && defined(HAVE_EXP)double result = exp(log(x) * 0.5);std::cout << "Computing sqrt of " << x << " to be " << result<< " using log and exp" << std::endl; #elsedouble result = x;

修改mysqrt.cxx?來包含?cmath.

#include <cmath>

Step 6：增加一個客制化的命令和產生的文件

在MathFunctions的目錄中，一個新的源文件MakeTable.cxx,被用來產生已經計算出來的值。接下來在Math/CMakeLists.txt中，增加恰當的命令來編譯可執行的MakeTable和運行它。

MathFunctions/CMakeLists.txt的頭部增加：

add_executable(MakeTable MakeTable.cxx)

然后，我們增加一個客制化的命令，運行MakeTable,來產生Table.h.

Then we add a custom command that specifies how to produce?Table.h?by running MakeTable.

add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/Table.hCOMMAND MakeTable ${CMAKE_CURRENT_BINARY_DIR}/Table.hDEPENDS MakeTable)

接下來，必須讓CMake直到mysqrt.cxxx依賴于這個Table.h.This is done by adding the generated?Table.h?to the list of sources for the library MathFunctions.

add_library(MathFunctionsmysqrt.cxx${CMAKE_CURRENT_BINARY_DIR}/Table.h)

我們也必須增加Table.h到目前的二進制目錄中，以便于它可以被找到。

target_include_directories(MathFunctionsINTERFACE ${CMAKE_CURRENT_SOURCE_DIR}PRIVATE ${CMAKE_CURRENT_BINARY_DIR})

修改mysqrt.cxx來包含Table.h,接下來就可以重寫mysqrt方法來使用這個表。

step 7: 編譯和安裝

如果我們想發布我們程序給其他人使用。使用CPacke來創建平臺指定的安裝器，來編譯不同平臺的二進制安裝包等。需要在上一級的CMakeLists.txt中增加：

include(InstallRequiredSystemLibraries) set(CPACK_RESOURCE_FILE_LICENSE "${CMAKE_CURRENT_SOURCE_DIR}/License.txt") set(CPACK_PACKAGE_VERSION_MAJOR "${Tutorial_VERSION_MAJOR}") set(CPACK_PACKAGE_VERSION_MINOR "${Tutorial_VERSION_MINOR}") include(CPack)

這個module將會包含當前平臺項目所需要的任何運行時庫。

cpack -G ZIP -C Debug cpack --config CPackSourceConfig.cmake

step 8：Adding Support for a Dashboard

為了支持輸出dashboards，在頂級的CMakeLists.txt中，做修改如下：

?

Replace:

# enable testing enable_testing()

With:

# enable dashboard scripting include(CTest)

在頂級目錄，我們需要創建一個CTestConfig.cmake的文件，可以指定項目的名稱和要提供的dashboard。

set(CTEST_PROJECT_NAME "CMakeTutorial") set(CTEST_NIGHTLY_START_TIME "00:00:00 EST")set(CTEST_DROP_METHOD "http") set(CTEST_DROP_SITE "my.cdash.org") set(CTEST_DROP_LOCATION "/submit.php?project=CMakeTutorial") set(CTEST_DROP_SITE_CDASH TRUE) ctest [-VV] -C Debug -D Experimental

Step 9：混合靜態和共享

使用option來定義一個開關，增加一個BUILD_SHARED_LIBS到頂級CMakeLists.txt中。

cmake_minimum_required(VERSION 3.10)# set the project name and version project(Tutorial VERSION 1.0)# specify the C++ standard set(CMAKE_CXX_STANDARD 11) set(CMAKE_CXX_STANDARD_REQUIRED True)# control where the static and shared libraries are built so that on windows # we don't need to tinker with the path to run the executable set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY "${PROJECT_BINARY_DIR}") set(CMAKE_LIBRARY_OUTPUT_DIRECTORY "${PROJECT_BINARY_DIR}") set(CMAKE_RUNTIME_OUTPUT_DIRECTORY "${PROJECT_BINARY_DIR}")option(BUILD_SHARED_LIBS "Build using shared libraries" ON)# configure a header file to pass the version number only configure_file(TutorialConfig.h.in TutorialConfig.h)# add the MathFunctions library add_subdirectory(MathFunctions)# add the executable add_executable(Tutorial tutorial.cxx) target_link_libraries(Tutorial PUBLIC MathFunctions)

在MathFunctions/CMakeLists.txt中，我們需要根據USE_MyMATH是否打開，來創建一個SqrtLibrary。

# add the library that runs add_library(MathFunctions MathFunctions.cxx)# state that anybody linking to us needs to include the current source dir # to find MathFunctions.h, while we don't. target_include_directories(MathFunctionsINTERFACE ${CMAKE_CURRENT_SOURCE_DIR})# should we use our own math functions option(USE_MYMATH "Use tutorial provided math implementation" ON) if(USE_MYMATH)target_compile_definitions(MathFunctions PRIVATE "USE_MYMATH")# first we add the executable that generates the tableadd_executable(MakeTable MakeTable.cxx)# add the command to generate the source codeadd_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/Table.hCOMMAND MakeTable ${CMAKE_CURRENT_BINARY_DIR}/Table.hDEPENDS MakeTable)# library that just does sqrtadd_library(SqrtLibrary STATICmysqrt.cxx${CMAKE_CURRENT_BINARY_DIR}/Table.h)# state that we depend on our binary dir to find Table.htarget_include_directories(SqrtLibrary PRIVATE${CMAKE_CURRENT_BINARY_DIR})target_link_libraries(MathFunctions PRIVATE SqrtLibrary) endif()# define the symbol stating we are using the declspec(dllexport) when # building on windows target_compile_definitions(MathFunctions PRIVATE "EXPORTING_MYMATH")# install rules set(installable_libs MathFunctions) if(TARGET SqrtLibrary)list(APPEND installable_libs SqrtLibrary) endif() install(TARGETS ${installable_libs} DESTINATION lib) install(FILES MathFunctions.h DESTINATION include)

最后更新?MathFunctions/MathFunctions.h?to use dll export defines:

#if defined(_WIN32) # if defined(EXPORTING_MYMATH) # define DECLSPEC __declspec(dllexport) # else # define DECLSPEC __declspec(dllimport) # endif #else // non windows # define DECLSPEC #endifnamespace mathfunctions { double DECLSPEC sqrt(double x); } # state that SqrtLibrary need PIC when the default is shared librariesset_target_properties(SqrtLibrary PROPERTIESPOSITION_INDEPENDENT_CODE ${BUILD_SHARED_LIBS})target_link_libraries(MathFunctions PRIVATE SqrtLibrary)

Step 10：增加Generator 表達式

Generator?expressions：

在生成生成系統期間進行評估，以生成特定于每個生成配置的信息；

允許在許多目標屬性的上下文中使用，例如鏈接\庫、包含\目錄、編譯\定義等。在使用命令填充這些屬性時，也可以使用它們，例如target\u link\u libraries（）、target\u include\u directories（）、target\u compile\u definitions（）和其他命令。

可用于啟用條件鏈接、編譯時使用的條件定義、條件包含目錄等。條件可能基于構建配置、目標屬性、平臺信息或任何其他可查詢信息

包括邏輯，信息和輸出表達式。

?A?$<0:...>?results in the empty string, and?<1:...>?results in the content of "...". They can also be nested.

下面的代碼：

# specify the C++ standard set(CMAKE_CXX_STANDARD 11) set(CMAKE_CXX_STANDARD_REQUIRED True)

可以被替換為：

add_library(tutorial_compiler_flags INTERFACE) target_compile_features(tutorial_compiler_flags INTERFACE cxx_std_11) set(gcc_like_cxx "$<COMPILE_LANG_AND_ID:CXX,ARMClang,AppleClang,Clang,GNU>") set(msvc_cxx "$<COMPILE_LANG_AND_ID:CXX,MSVC>") target_compile_options(tutorial_compiler_flags INTERFACE"$<${gcc_like_cxx}:$<BUILD_INTERFACE:-Wall;-Wextra;-Wshadow;-Wformat=2;-Wunused>>""$<${msvc_cxx}:$<BUILD_INTERFACE:-W3>>" )

Step 11. 增加導出配置

第一步，更新我們的install(TARGETS）命令不僅僅指定一個DESTINATION，而且指定EXPORT。這EXPORT關鍵字產生和安裝一個CMake 文件包含代碼來的導入被列在和安裝安裝命令在安裝樹。在MathFunctions/CMakeLists.txt，我們可以明確使用EXPORT，來導出MathFunctions庫，通過更新安裝命令。

set(installable_libs MathFunctions tutorial_compiler_flags) if(TARGET SqrtLibrary)list(APPEND installable_libs SqrtLibrary) endif() install(TARGETS ${installable_libs}DESTINATION libEXPORT MathFunctionsTargets) install(FILES MathFunctions.h DESTINATION include)

現在我們已經導出了MathFunctions，我們也需要明確安裝產生的MathFunctionsTargets.cmake文件。通過增加下面到頂層的CMakeLists.txt:

install(EXPORT MathFunctionsTargetsFILE MathFunctionsTargets.cmakeDESTINATION lib/cmake/MathFunctions )

它將導出一個路徑和當前的機器綁定。這個解決方法是更新? MathFunctions?target_include_directories()?來理解，它需要不同的INTERFACE位置，當在編譯目錄和來自一個install/packate。?This means converting the?target_include_directories()?call for MathFunctions to look like:

target_include_directories(MathFunctionsINTERFACE$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>$<INSTALL_INTERFACE:include>)

?

這時，CMake已經恰當的打包了目標信息，但是我們仍然需要產生一個MathFunctionsConfig.cmake,以至于CMake可以通過find_package命令來找到我們的項目。增加一個新文件Config.cmake.in,內容如下：

@PACKAGE_INIT@include ( "${CMAKE_CURRENT_LIST_DIR}/MathFunctionsTargets.cmake" )

為了恰當的配置和安裝這個文件，增加下面的內容到頂層的CMakeLists.txt:

install(EXPORT MathFunctionsTargetsFILE MathFunctionsTargets.cmakeDESTINATION lib/cmake/MathFunctions )include(CMakePackageConfigHelpers) # generate the config file that is includes the exports configure_package_config_file(${CMAKE_CURRENT_SOURCE_DIR}/Config.cmake.in"${CMAKE_CURRENT_BINARY_DIR}/MathFunctionsConfig.cmake"INSTALL_DESTINATION "lib/cmake/example"NO_SET_AND_CHECK_MACRONO_CHECK_REQUIRED_COMPONENTS_MACRO) # generate the version file for the config file write_basic_package_version_file("${CMAKE_CURRENT_BINARY_DIR}/MathFunctionsConfigVersion.cmake"VERSION "${Tutorial_VERSION_MAJOR}.${Tutorial_VERSION_MINOR}"COMPATIBILITY AnyNewerVersion )# install the configuration file install(FILES${CMAKE_CURRENT_BINARY_DIR}/MathFunctionsConfig.cmakeDESTINATION lib/cmake/MathFunctions)

此時，我們已經產生了一個可以用于已經安裝或者打包的項目的relocatable的CMake配置文件。如果我們想我們的項目，從編譯的目錄可以被使用。我們在頂層的CMakeLists.txt的底部增加：

export(EXPORT MathFunctionsTargetsFILE "${CMAKE_CURRENT_BINARY_DIR}/MathFunctionsTargets.cmake" )

Step 12：Debug和release

Set?CMAKE_DEBUG_POSTFIX?near the beginning of the top-level?CMakeLists.txt?file:

set(CMAKE_DEBUG_POSTFIX d)add_library(tutorial_compiler_flags INTERFACE)

And the?DEBUG_POSTFIX?property on the tutorial executable:

add_executable(Tutorial tutorial.cxx) set_target_properties(Tutorial PROPERTIES DEBUG_POSTFIX ${CMAKE_DEBUG_POSTFIX})target_link_libraries(Tutorial PUBLIC MathFunctions)

Let's also add version numbering to the MathFunctions library. In?MathFunctions/CMakeLists.txt, set the?VERSION?and?SOVERSION?properties:

set_property(TARGET MathFunctions PROPERTY VERSION "1.0.0") set_property(TARGET MathFunctions PROPERTY SOVERSION "1")

From the?Step12?directory, create?debug?and?release?subbdirectories. The layout will look like:

- Step12- debug- release

Now we need to setup debug and release builds. We can use?CMAKE_BUILD_TYPE?to set the configuration type:

cd debug cmake -DCMAKE_BUILD_TYPE=Debug .. cmake --build . cd ../release cmake -DCMAKE_BUILD_TYPE=Release .. cmake --build .

Now that both the debug and release builds are complete, we can use a custom configuration file to package both builds into a single release. In the?Step12?directory, create a file called?MultiCPackConfig.cmake. In this file, first include the default configuration file that was created by the?cmake?executable.

Next, use the?CPACK_INSTALL_CMAKE_PROJECTS?variable to specify which projects to install. In this case, we want to install both debug and release.

include("release/CPackConfig.cmake")set(CPACK_INSTALL_CMAKE_PROJECTS"debug;Tutorial;ALL;/""release;Tutorial;ALL;/")

From the?Step12?directory, run?cpack?specifying our custom configuration file with the?config?option:

cpack --config MultiCPackConfig.cmake

?

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