（5）CMake入門筆記--CMake官網教程

五．添加生成的文件和生成器

在本節中，我們將展示如何將生成的源文件添加到應用程序的構建過程中。 對於此示例，我們將創建一個預先計算的平方根表，作爲構建過程的一部分，然後將該表編譯到我們的應用程序中。 爲此，我們首先需要一個生成表的程序。 在MathFunctions子目錄中，一個名爲MakeTable.cxx的新源文件就是這樣做的。

// A simple program that builds a sqrt table
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main (int argc, char *argv[])
{
  int i;
  double result;

  // make sure we have enough arguments
  if (argc < 2)
  {
    return 1;
  }

  // open the output file
  FILE *fout = fopen(argv[1],"w");
  if (!fout)
  {
    return 1;
  }

  // create a source file with a table of square roots
  fprintf(fout,"double sqrtTable[] = {\n");
  for (i = 0; i < 10; ++i)
  {
    result = sqrt(static_cast<double>(i));
    fprintf(fout,"%g,\n",result);
  }

  // close the table with a zero
  fprintf(fout,"0};\n");
  fclose(fout);
  return 0;
}

請注意，該表是作爲有效的C ++代碼生成的，並且將輸出的文件的名稱作爲參數傳入。 下一步是將適當的命令添加到MathFunctions的CMakeLists.txt文件以構建MakeTable可執行文件，然後在構建過程中運行它。 完成此操作需要一些命令，如下所示。

# 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
  )

# add the binary tree directory to the search path for
# include files
include_directories( ${CMAKE_CURRENT_BINARY_DIR} )

# add the main library
add_library(MathFunctions mysqrt.cxx ${CMAKE_CURRENT_BINARY_DIR}/Table.h  )

首先添加MakeTable的可執行文件。 然後我們添加一個自定義命令，指定如何通過運行MakeTable來生成Table.h。 接下來我們要讓CMake知道mysqrt.cxx依賴於生成的文件Table.h。 這是通過將生成的Table.h添加到庫MathFunctions的源列表中完成的。 我們還必須將當前二進制目錄添加到包含目錄列表中，以便可以在mysqrt.cxx中找到幷包含Table.h。 構建此項目時，它將首先構建MakeTable可執行文件（DEPENDS MakeTable的作用，如果可執行已有則可以沒有這句話）。 然後它將運行MakeTable以生成Table.h。 最後，它將編譯包含Table.h的mysqrt.cxx以生成MathFunctions庫。 此時，頂級CMakeLists.txt文件包含我們添加的所有功能，如下所示：

cmake_minimum_required (VERSION 2.6)
project (Tutorial)
include(CTest)

# The version number.
set (Tutorial_VERSION_MAJOR 1)
set (Tutorial_VERSION_MINOR 0)

# does this system provide the log and exp functions?
include (${CMAKE_ROOT}/Modules/CheckFunctionExists.cmake)

check_function_exists (log HAVE_LOG)
check_function_exists (exp HAVE_EXP)

# should we use our own math functions
option(USE_MYMATH
  "Use tutorial provided math implementation" ON)

# configure a header file to pass some of the CMake settings
# to the source code
configure_file (
  "${PROJECT_SOURCE_DIR}/TutorialConfig.h.in"
  "${PROJECT_BINARY_DIR}/TutorialConfig.h"
  )

# add the binary tree to the search path for include files
# so that we will find TutorialConfig.h
include_directories ("${PROJECT_BINARY_DIR}")

# add the MathFunctions library?
if (USE_MYMATH)
  include_directories ("${PROJECT_SOURCE_DIR}/MathFunctions")
  add_subdirectory (MathFunctions)
  set (EXTRA_LIBS ${EXTRA_LIBS} MathFunctions)
endif (USE_MYMATH)

# add the executable
add_executable (Tutorial tutorial.cxx)
target_link_libraries (Tutorial  ${EXTRA_LIBS})

# add the install targets
install (TARGETS Tutorial DESTINATION bin)
install (FILES "${PROJECT_BINARY_DIR}/TutorialConfig.h"       
         DESTINATION include)

# does the application run
add_test (TutorialRuns Tutorial 25)

# does the usage message work?
add_test (TutorialUsage Tutorial)
set_tests_properties (TutorialUsage
  PROPERTIES
  PASS_REGULAR_EXPRESSION "Usage:.*number"
  )

#define a macro to simplify adding tests
macro (do_test arg result)
  add_test (TutorialComp${arg} Tutorial ${arg})
  set_tests_properties (TutorialComp${arg}
    PROPERTIES PASS_REGULAR_EXPRESSION ${result}
    )
endmacro (do_test)

# do a bunch of result based tests
do_test (4 "4 is 2")
do_test (9 "9 is 3")
do_test (5 "5 is 2.236")
do_test (7 "7 is 2.645")
do_test (25 "25 is 5")
do_test (-25 "-25 is 0")
do_test (0.0001 "0.0001 is 0.01")
TutorialConfig.h.in如下：
// the configured options and settings for Tutorial
#define Tutorial_VERSION_MAJOR @Tutorial_VERSION_MAJOR@
#define Tutorial_VERSION_MINOR @Tutorial_VERSION_MINOR@
#cmakedefine USE_MYMATH

// does the platform provide exp and log functions?
#cmakedefine HAVE_LOG
#cmakedefine HAVE_EXP

MathFunctions的CMakeLists.txt文件如下所示：

# 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
  DEPENDS MakeTable
  COMMAND MakeTable ${CMAKE_CURRENT_BINARY_DIR}/Table.h
  )
# add the binary tree directory to the search path
# for include files
include_directories( ${CMAKE_CURRENT_BINARY_DIR} )

# add the main library
add_library(MathFunctions mysqrt.cxx ${CMAKE_CURRENT_BINARY_DIR}/Table.h)

install (TARGETS MathFunctions DESTINATION bin)
install (FILES MathFunctions.h DESTINATION include)