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Diffstat (limited to 'Tests/Tutorial/Step9/directions.txt')
| -rw-r--r-- | Tests/Tutorial/Step9/directions.txt | 166 |
1 files changed, 0 insertions, 166 deletions
diff --git a/Tests/Tutorial/Step9/directions.txt b/Tests/Tutorial/Step9/directions.txt deleted file mode 100644 index 8771637..0000000 --- a/Tests/Tutorial/Step9/directions.txt +++ /dev/null @@ -1,166 +0,0 @@ -# Mixing Static and Shared # - -In this section we will show how by using the BUILD_SHARED_LIBS variable we can -control the default behavior of add_library, and allow control over how -libraries without an explicit type ( STATIC/SHARED/MODULE/OBJECT ) are built. - -To accomplish this we need to add BUILD_SHARED_LIBS to the top level -CMakeLists.txt. We use the option command as it allows users to optionally -select if the value should be On or Off. - -Next we are going to refactor MathFunctions to become a real library that -encapsulates using mysqrt or sqrt, instead of requiring the calling code -to do this logic. This will also mean that USE_MYMATH will not control building -MathFuctions, but instead will control the behavior of this library. - -The first step is to update the starting section of the top level CMakeLists.txt -to look like: - - cmake_minimum_required(VERSION 3.3) - project(Tutorial) - - # 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_CXX_STANDARD 11) - set(CMAKE_CXX_STANDARD_REQUIRED True) - - option(BUILD_SHARED_LIBS "Build using shared libraries" ON) - - # the version number. - set(Tutorial_VERSION_MAJOR 1) - set(Tutorial_VERSION_MINOR 0) - - # configure a header file to pass the version number only - configure_file( - "${PROJECT_SOURCE_DIR}/TutorialConfig.h.in" - "${PROJECT_BINARY_DIR}/TutorialConfig.h" - ) - - # add the MathFunctions library - add_subdirectory(MathFunctions) - - # add the executable - add_executable(Tutorial tutorial.cxx) - target_link_libraries(Tutorial PUBLIC MathFunctions) - -Now that we have made MathFunctions always be used, we will need to update -the logic of that library. So, in MathFunctions/CMakeLists.txt we need to -create a SqrtLibrary that will conditionally be built when USE_MYMATH is -enabled. Now, since this is a tutorial, we are going to explicitly require -that SqrtLibrary is built statically. - -The end result is that MathFunctions/CMakeLists.txt should look like: - - # 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(MathFunctions - INTERFACE ${CMAKE_CURRENT_SOURCE_DIR} - ) - - # should we use our own math functions - option(USE_MYMATH "Use tutorial provided math implementation" ON) - if(USE_MYMATH) - - # does this system provide the log and exp functions? - include(CheckSymbolExists) - set(CMAKE_REQUIRED_LIBRARIES "m") - check_symbol_exists(log "math.h" HAVE_LOG) - check_symbol_exists(exp "math.h" HAVE_EXP) - - # first we add the executable that generates the table - add_executable(MakeTable MakeTable.cxx) - - # add the command to generate the source code - add_custom_command( - OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/Table.h - COMMAND MakeTable ${CMAKE_CURRENT_BINARY_DIR}/Table.h - DEPENDS MakeTable - ) - - # library that just does sqrt - add_library(SqrtLibrary STATIC - mysqrt.cxx - ${CMAKE_CURRENT_BINARY_DIR}/Table.h - ) - - # state that we depend on our binary dir to find Table.h - target_include_directories(SqrtLibrary PRIVATE - ${CMAKE_CURRENT_BINARY_DIR} - ) - - target_compile_definitions(MathFunctions PRIVATE "USE_MYMATH") - if(HAVE_LOG AND HAVE_EXP) - target_compile_definitions(SqrtLibrary - PRIVATE "HAVE_LOG" "HAVE_EXP") - endif() - - 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(TARGETS MathFunctions DESTINATION lib) - install(FILES MathFunctions.h DESTINATION include) - -Next, update MathFunctions/mysqrt.cxx to use the mathfunctions and detail namespaces: - - #include <iostream> - #include "MathFunctions.h" - - // include the generated table - #include "Table.h" - - #include <cmath> - - namespace mathfunctions { - namespace detail { - // a hack square root calculation using simple operations - double mysqrt(double x) - { - ... - - return result; - } - } - } - -We also need to make some changes in tutorial.cxx, so that it no longer uses USE_MYMATH: -1. Always include MathFunctions.h -2. Always use mathfunctions::sqrt - -Finally, update 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 - #endif - - namespace mathfunctions - { - double DECLSPEC sqrt(double x); - } - -At this point, if you build everything, you will notice that linking fails -as we are combining a static library without position enabled code with a -library that has position enabled code. This solution to this is to explicitly -set the POSITION_INDEPENDENT_CODE target property of SqrtLibrary to be True no -matter the build type. - -Exercise: We modified MathFunctions.h to use dll export defines. Using CMake -documentation can you find a helper module to simplify this? - -Exercise: Determine what command is enabling PIC for SqrtLibrary. -What happens if we remove said command? |