（1）引用自定义头文件

自定义一个头文件：add_count.h，预定义 INIT_COUNT = 89 ;函数 add_num()

#ifndef _add_count_
#define _add_count_


#define INIT_COUNT 89

int add_num(int a , int b);


#endif

创建package_h_learn包，
修改CMakeLists.txt： 指定头文件位置，在include文件夹，将.h文件放入include文件夹

## Specify additional locations of header files
## Your package locations should be listed before other locations
include_directories(
 include
  ${catkin_INCLUDE_DIRS}
)
....
....
....
add_executable(h_learn src/h_learn.cpp)
target_link_libraries(h_learn ${catkin_LIBRARIES})

h_learn.cpp代码：

#include "ros/ros.h"
#include "std_msgs/String.h"
#include <sstream>

#include "package_h_learn/add_count.h" //引用自定义的头文件

int add_num(int a , int b)	//头文件函数声明的实现
{
	int sum;
	sum = a + b;
	return sum;
}

int main(int argc, char **argv)
{
    ros::init(argc,argv,"h_learn");
    ros::NodeHandle n;
    ros::Publisher pub = n.advertise<std_msgs::String>("listener",1000);
    ros::Rate loop_rate(10);
    
    int count =INIT_COUNT;	//头文件宏定义初始化INIT_COUNT
    int num;
    num = add_num(count,5);

    while(ros::ok())
    {
        std_msgs::String msg;
        std::stringstream ss;

        ss<<"Hello world  "<<num;

        msg.data = ss.str();
        ROS_INFO(msg.data.c_str());
        pub.publish(msg);
        ros::spinOnce();
        loop_rate.sleep();
    }

    return 0;
}

（2）引用同一工作空间的头文件

创建test_package包,在CMakeList.txt修改：

add_executable(h_learn src/h_learn.cpp)
target_link_libraries(h_learn ${catkin_LIBRARIES})

需要引用的头文件在另一个包package_h_learn的include中，所以需要将package_h_learn中的CMakeList.txt做一些修改：将 include文件夹的头文件 发布出去

###################################
## catkin specific configuration ##
###################################
## The catkin_package macro generates cmake config files for your package
## Declare things to be passed to dependent projects
## INCLUDE_DIRS: uncomment this if your package contains header files
## LIBRARIES: libraries you create in this project that dependent projects also need
## CATKIN_DEPENDS: catkin_packages dependent projects also need
## DEPENDS: system dependencies of this project that dependent projects also need
catkin_package(
  INCLUDE_DIRS include
#  LIBRARIES package_h_learn
#  CATKIN_DEPENDS roscpp rospy std_msgs
#  DEPENDS system_lib
)

tesk_pkg.cpp代码如下：

#include "ros/ros.h"
#include "std_msgs/String.h"
#include <sstream>

#include "package_h_learn/add_count.h"  //引用其它包（package_h_learn）的头文件

int add_num(int a , int b)	//头文件函数声明的实现
{
	int sum;
	sum = a + b;
	return sum;
}

int main(int argc, char **argv)
{
    ros::init(argc,argv,"h_learn");
    ros::NodeHandle n;
    ros::Publisher pub = n.advertise<std_msgs::String>("listener",1000);
    ros::Rate loop_rate(10);
    
    int count =INIT_COUNT;	//头文件宏定义初始化INIT_COUNT
    int num;
    num = add_num(count,15);

    while(ros::ok())
    {
        std_msgs::String msg;
        std::stringstream ss;

        ss<<"Hello world  "<<num;

        msg.data = ss.str();
        ROS_INFO(msg.data.c_str());
        pub.publish(msg);
        ros::spinOnce();
        loop_rate.sleep();
    }

    return 0;
}

（3）引用动态链接库

首先自己创建一个简单的动态链接库用于测试：首先创建multiply.cpp和multiply.h
multiply.cpp

#include "multiply.h"

int multiply(int a, int b)
{
	return a*b;
}

multiply.h

#ifndef _MULTIPLY_H_
#define _MULTIPLY_H_

#ifndef __cpluscplus
extern "C"
{
#endif

	int multiply(int a, int b);

#ifndef __cpluscplus
}
#endif

#endif

接下来生成动态链接库*.so文件，注意-share 和 -fPIC 参数很重要
-share:告诉gcc要生成的是动态链接库
-fPIC:告诉gcc生成的代码是非位置依赖的，方便用于动态链接

g++ multiply.cpp -fPIC -shared -o libmultiply.so

在ros工作空间创建一个包test_package，multiply.h放在include目录下，libmultiply.so放在lib目录下。

CMakeLists.txt需要做如下修改：

1. include_directories ：需要包含头文件
2. link_directories ：用于添加第三方库路径，catkin_LIB_DIRS表示创建环境变量，${catkin_LIB_DIRS}为取该环境变量的值,lib是相对于当前软件包所在路径的相对路径
3. target_link_libraries ：引用动态链接库，这里去掉lib前缀，去掉.so，直接写multiply

## Specify additional locations of header files
## Your package locations should be listed before other locations
include_directories(
 include
  ${catkin_INCLUDE_DIRS}
)
link_directories(
 lib
  ${catkin_LIB_DIRS}
)

...
...
...
add_executable(test_pkg src/test_pkg.cpp)

#add_dependencies(h_learn test1_generate_message_cpp)

target_link_libraries(test_pkg 
	${catkin_LIBRARIES}
	multiply
)

src/test_pkg.cpp代码如下：

#include "ros/ros.h"
#include "std_msgs/String.h"
#include <sstream>

#include "test_package/multiply.h"


int main(int argc, char **argv)
{
    ros::init(argc,argv,"h_learn");
    ros::NodeHandle n;
    ros::Publisher pub = n.advertise<std_msgs::String>("listener",1000);
    ros::Rate loop_rate(10);

	//.so
	int num = multiply(5,5);
    while(ros::ok())
    {
        std_msgs::String msg;
        std::stringstream ss;

        ss<<"Hello world  "<<num;

        msg.data = ss.str();
        ROS_INFO(msg.data.c_str());
        pub.publish(msg);
        ros::spinOnce();
        loop_rate.sleep();
    }

    return 0;
}

结果：