你或许听过好几种 Make 工具，例如 GNU Make ，QT 的 qmake ，微软的 MS nmake，BSD Make（pmake），Makepp，等等。这些 Make 工具遵循着不同的规范和标准，所执行的 Makefile 格式也千差万别。这样就带来了一个严峻的问题：如果软件想跨平台，必须要保证能够在不同平台编译。而如果使用上面的 Make 工具，就得为每一种标准写一次 Makefile ，这将是一件让人抓狂的工作。
CMake 就是针对上面问题所设计的工具：它首先允许开发者编写一种平台无关的 CMakeLists.txt 文件来定制整个编译流程，然后再根据目标用户的平台进一步生成所需的本地化 Makefile 和工程文件，如 Unix 的 Makefile 或 Windows 的 Visual Studio 工程。从而做到“Write once, run everywhere”。显然，CMake 是一个比上述几种 make 更高级的编译配置工具。一些使用 CMake 作为项目架构系统的知名开源项目有 VTK、ITK、KDE、OpenCV、OSG 等 [1]。
// A simple program that computes the square root of a number
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int main (int argc, char *argv[])
{
if (argc < 2)
{
fprintf(stdout,"Usage: %s number\n",argv[0]);
return 1;
}
double inputValue = atof(argv[1]);
double outputValue = sqrt(inputValue);
fprintf(stdout,"The square root of %g is %g\n",
inputValue, outputValue);
return 0;
}
添加版本号，配置头文件 CMakeLists.txt
# Basic two lines.(cmake version & project name)
cmake_minimum_required (VERSION 2.6)
project (Tutorial)
# Add the version number.
set (Tutorial_VERSION_MAJOR 1)
set (Tutorial_VERSION_MINOR 0)
# 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 executable
add_executable(Tutorial tutorial.cxx)
// Define the configured options and settings for Tutorial
#define Tutorial_VERSION_MAJOR @Tutorial_VERSION_MAJOR@
#define Tutorial_VERSION_MINOR @Tutorial_VERSION_MINOR@
// A simple program that computes the square root of a number
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "TutorialConfig.h"
int main (int argc, char *argv[])
{
// Print the version info stored in configuration file.
if (argc < 2)
{
fprintf(stdout,"%s Version %d.%d\n",
argv[0],
Tutorial_VERSION_MAJOR,
Tutorial_VERSION_MINOR);
fprintf(stdout,"Usage: %s number\n",argv[0]);
return 1;
}
double inputValue = atof(argv[1]);
double outputValue = sqrt(inputValue);
fprintf(stdout,"The square root of %g is %g\n",
inputValue, outputValue);
return 0;
}
#include "MathFunctions.h"
#include <stdio.h>
// a hack square root calculation using simple operations
double mysqrt(double x)
{
if (x <= 0)
{
return 0;
}
double result;
double delta;
result = x;
// do ten iterations
int i;
for (i = 0; i < 10; ++i)
{
if (result <= 0)
{
result = 0.1;
}
delta = x - (result * result);
result = result + 0.5 * delta / result;
fprintf(stdout, "Computing sqrt of %g to be %g\n", x, result);
}
return result;
}
以上就是安装的全部步骤。现在你应该可以编译本教程了。输入 make install（或在 IDE 中编译 install 项目），对应的头文件、库文件和可执行文件就会被安装。CMake 的 CMAKE_INSTALL_PREFIX 参数可以指定安装文件的根目录（之前还可以加上 -D 参数，具体意义可以参考 what does the parameter "-D" mean）。添加测试过程同样简单明了。在顶层 CMakeLists.txt 文件的最后我们可以添加一个基础测试数据来验证该应用程序是否正常运行。
include(CTest)
# does the application run
add_test (TutorialRuns Tutorial 25)
# does it sqrt of 25
add_test (TutorialComp25 Tutorial 25)
set_tests_properties (TutorialComp25 PROPERTIES PASS_REGULAR_EXPRESSION "25 is 5")
# does it handle negative numbers
add_test (TutorialNegative Tutorial -25)
set_tests_properties (TutorialNegative PROPERTIES PASS_REGULAR_EXPRESSION "-25 is 0")
# does it handle small numbers
add_test (TutorialSmall Tutorial 0.0001)
set_tests_properties (TutorialSmall PROPERTIES PASS_REGULAR_EXPRESSION "0.0001 is 0.01")
# 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, then use it
macro (do_test arg result)
add_test (TutorialComp${arg} Tutorial ${arg})
set_tests_properties (TutorialComp${arg}
PROPERTIES PASS_REGULAR_EXPRESSION ${result})
endmacro (do_test)
# do a bunch of result based tests
do_test (25 "25 is 5")
do_test (-25 "-25 is 0")
# does this system provide the log and exp functions?
include (${CMAKE_ROOT}/Modules/CheckFunctionExists.cmake)
check_function_exists (log HAVE_LOG)
check_function_exists (exp HAVE_EXP)
// if we have both log and exp then use them
#if defined (HAVE_LOG) && defined (HAVE_EXP)
result = exp(log(x)*0.5);
#else // otherwise use an iterative approach
. . .
// 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;
}
注意到这张表使用 C++ 代码生成且文件的名字通过输入参数指定。下一步通过在 MathFunctions 的 CMakeLists.txt 中添加合适的代码来构建 MakeTable 可执行文件，并将它作为构建的一部分运行。只需要一点代码就能实现这个功能：
# 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 ${CMAKE_CURRENT_BINARY_DIR}/Table.h )
cmake_minimum_required (VERSION 2.6)
project (Tutorial)
include(CTest)
# The version number.
set (Tutorial_VERSION_MAJOR 1)
set (Tutorial_VERSION_MINOR 0)
# does this system provide the log and exp functions?
include (${CMAKE_ROOT}/Modules/CheckFunctionExists.cmake)
# check the function exists? return bool value named HAVE_LOG/HAVE_EXP
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 文件如下：
// 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
最后 MathFunctions 的 CMakeLists.txt 文件如下：
# 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 ${CMAKE_CURRENT_BINARY_DIR}/Table.h)
install (TARGETS MathFunctions DESTINATION bin)
install (FILES MathFunctions.h DESTINATION include)
Step 6. 构造一个 Installer
接下来假设我们想将我们的项目发布给其他人以便供他们使用。我们想提供在不同平台上的二进制文件和源码的发布版本。这一点和我们在之前安装和测试章节（步骤3）略有不同，步骤三安装的二进制文件是我们从源码构建的。这里我们将构建一个支持二进制文件安装的安装包和可以在 cygwin,debian,RPMs 等中被找到的安装管理特性。为了实现这一点我们将使用 CPack 来创建在 Packaging with CPack 章节中介绍过的平台特定安装器（platform specific installers）。我们需要在顶层 CMakeLists.txt 文件添加以下几行内容：
# build a CPack driven installer package
include (InstallRequiredSystemLibraries)
set (CPACK_RESOURCE_FILE_LICENSE
"${CMAKE_CURRENT_SOURCE_DIR}/License.txt")
set (CPACK_PACKAGE_VERSION_MAJOR "${Tutorial_VERSION_MAJOR}")
set (CPACK_PACKAGE_VERSION_MINOR "${Tutorial_VERSION_MINOR}")
include (CPack)
本指南深入介绍了CMake的使用方法，包括构建工具的背景、基本配置、高级功能，如版本控制、条件编译、测试、安装及仪表盘支持。通过实践示例，详细讲解了如何利用CMakeLists.txt文件来定制编译流程。
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