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Diffstat (limited to 'Help/guide/tutorial/Step5/directions.txt')
| -rw-r--r-- | Help/guide/tutorial/Step5/directions.txt | 69 |
1 files changed, 0 insertions, 69 deletions
diff --git a/Help/guide/tutorial/Step5/directions.txt b/Help/guide/tutorial/Step5/directions.txt deleted file mode 100644 index e6f5197..0000000 --- a/Help/guide/tutorial/Step5/directions.txt +++ /dev/null @@ -1,69 +0,0 @@ -# Adding System Introspection # - -Let us consider adding some code to our project that depends on features the -target platform may not have. For this example, we will add some code that -depends on whether or not the target platform has the log and exp functions. Of -course almost every platform has these functions but for this tutorial assume -that they are not common. - -If the platform has log and exp then we will use them to compute the square -root in the mysqrt function. We first test for the availability of these -functions using the CheckSymbolExists.cmake macro in the top-level CMakeLists -file as follows: - - # 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) - -Now let's add these defines to TutorialConfig.h.in so that we can use them -from mysqrt.cxx: - - // does the platform provide exp and log functions? - #cmakedefine HAVE_LOG - #cmakedefine HAVE_EXP - -Modify mysqrt.cxx to include math.h. Next, in the mysqrt function we can -provide an alternate implementation based on log and exp if they are available -on the system using the following code: - - // if we have both log and exp then use them - #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" << std::endl; - #else - ... - -Run cmake or cmake-gui to configure the project and then build it with your -chosen build tool. - -You will notice that even though HAVE_LOG and HAVE_EXP are both defined mysqrt -isn't using them. We should realize quickly that we have forgotten to include -TutorialConfig.h in mysqrt.cxx. We will also need to update -MathFunctions/CMakeLists.txt with where it is located. - -So let's go ahead and update MathFunctions/CMakeLists.txt to look like: - - add_library(MathFunctions mysqrt.cxx) - - target_include_directories(MathFunctions - INTERFACE ${CMAKE_CURRENT_SOURCE_DIR} - PRIVATE ${Tutorial_BINARY_DIR} - ) - - install(TARGETS MathFunctions DESTINATION lib) - install(FILES MathFunctions.h DESTINATION include) - -Now all we need to do is include TutorialConfig.h in mysqrt.cxx - -At this point you should go ahead and build the project again. - -Run the built Tutorial executable. Which function gives better results now, -Step1’s sqrt or Step5’s mysqrt? - -Exercise: Why is it important that we configure TutorialConfig.h.in after the -checks for HAVE_LOG and HAVE_EXP? What would happen if we inverted the two? - -Exercise: Is there a better place for us to save the HAVE_LOG and HAVE_EXP -values other than in TutorialConfig.h? |