CMake 简明教程（5）---编译中使用间接生成的文件

时间：2022-08-31 19:22:33

原文网址：http://cmake.org/cmake/help/cmake_tutorial.html
教程中所有的代码都可以在这里找到：http://public.kitware.com/cgi-bin/viewcvs.cgi/CMake/Tests/Tutorial/




在这一节中，我们会展示如何在项目的编译过程中使用一个间接生成的文件。例如我们建立一个保存事先计算好的平方根的表做为编译的一部分，之后将这个表编译到我们的应用中。要完成这一功能，我们首先需要一个程序生成这个表。我们用在MathFunctions子目录下新建的MakeTable.cxx来完成这一工作：


// 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;
}

注意，这个表是使用C++代码生成的，并且输出文件名也通过参数传了过去。接下来就是在CMakeLists.txt中添加合适的命令来编译MakeTable 可执行文件，然后在编译过程中运行这个可执行文件。要实现这一功能，需要添加一些代码，如下：

# 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   #输出文件
  COMMAND MakeTable ${CMAKE_CURRENT_BINARY_DIR}/Table.h  # MakeTable是第二行编译出的可执行文件，接下来是输出文件名
  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，编译MakeTable可执行文件的过程如往常一样。然后，我们添加一个通过运行MakeTable生成Table.h的自定义命令。之后，我们让cmake知道mysqrt.cxx依赖于生成的Table.h。这是通过将生成的Table.h添加到MathFunctions所需的代码文件实现的。我们也需要include生成的Table.h的目录，让编译器找得到Table.h。

当编译项目时，MakeTable会被首先编译出来。之后MakeTable会被运行来生成Table.h。最后，include了Table.h的mysqt.cxx文件会被编译来生成MathFunctions库。

现在，完整的顶层的CMakeLists.txt如下所示：


cmake_minimum_required (VERSION 2.6)
project (Tutorial)
 
# 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内容如下：

// 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子目录的CMakeLists.txt内容如下：

# 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)





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