cmake教程step 2

step 2  向项目中添加库

　　在这一步中，我们实现自己到sqrt函数，并用CMakeLists.txt添加到我们到项目中. 

首先，我们在项目目录中增加一个子目录 : MathFunctions，用来放置我们的sqrt的实现.  我们在MathFunctions目录下创建两个文件： mysqrt.c 和 mysqrt.h

内容分别为

mysqrt.h:

float mysqrt(float) ;

mysqrt.c:

#include "mysqrt.h"
float mysqrt(float x)     {
    return x*x;
}

然后向在MathFunctions目录下创建 CMakeLists.txt 并 添加如下内容：

add_library(MathFunctions mysqrt.c)

最后的顶层目录下到CMakeLists.txt文件如下：

cmake_minimum_required (VERSION 2.6)
project (Tutorial)
# 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}")

19 
include_directories ("${PROJECT_SOURCE_DIR}/MathFunctions")
add_subdirectory (MathFunctions) 
 
# add the executable
add_executable(Tutorial hello.c)
target_link_libraries (Tutorial MathFunctions)

现在我们考虑将MathFunctions库变成可配置的，可在项目顶层目录中的CMakeLists.txt中添加下面到代码可以实现：

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

# 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.c)
target_link_libraries (Tutorial  ${EXTRA_LIBS})