1.首先在功能包创建一个srv文件夹

如上图所示，vehicle_control是我的功能包，创建一个srv文件夹

2.使用touch指令创建服务文件

touch Ranging.srv

3.在文件内输入服务数据

横线代表分割符，上面的是客户端发送的数据，下面是服务器返回的数据

具体使用什么类型参考自己的项目，以及ros支持类型

4.注册ROS

修改package.xml
在package.xml中添加如下代码，注意添加的位置，放在之前。（上一步自定义msg时已完成）

  <build_depend>message_generation</build_depend>
  <exec_depend>message_runtime</exec_depend>

修改CMakeLists.txt
在find_package中添加message_generation（已完成）

find_package(catkin REQUIRED COMPONENTS
   roscpp
   rospy
   std_msgs
   message_generation
)

取消add_service_files的注释，并把刚刚定义的消息文件添加进去

add_service_files(
  FILES
  AddTwoInts_alone.srv
  IsOpenyuntai.srv
  Ranging.srv
  )

在catkin_package中添加CATKIN_DEPENDS message_runtime

catkin_package(
#  INCLUDE_DIRS include
#  LIBRARIES beginner_tutorials
    CATKIN_DEPENDS roscpp rospy std_msgs message_runtime
#  DEPENDS system_lib
)

完成以上工作后，编译整个工作空间

cd ~/car
catkin_make

显示已经做好的服务
rossrv show vehicle_control/Ranging.srv

完成
5.服务的使用
客户端

import rospy

# imports the AddTwoInts service 
from rospy_tutorials.srv import *

## add two numbers using the add_two_ints service
## @param x int: first number to add
## @param y int: second number to add
def add_two_ints_client(x, y):

    # NOTE: you don't have to call rospy.init_node() to make calls against
    # a service. This is because service clients do not have to be
    # nodes.

    # block until the add_two_ints service is available
    # you can optionally specify a timeout
    rospy.wait_for_service('add_two_ints')
    
    try:
        # create a handle to the add_two_ints service
        add_two_ints = rospy.ServiceProxy('add_two_ints', AddTwoInts)
        
        print "Requesting %s+%s"%(x, y)
        
        # simplified style
        resp1 = add_two_ints(x, y)

        # formal style
        resp2 = add_two_ints.call(AddTwoIntsRequest(x, y))

        if not resp1.sum == (x + y):
            raise Exception("test failure, returned sum was %s"%resp1.sum)
        if not resp2.sum == (x + y):
            raise Exception("test failure, returned sum was %s"%resp2.sum)
        return resp1.sum
    except rospy.ServiceException, e:
        print "Service call failed: %s"%e

def usage():
    return "%s [x y]"%sys.argv[0]

if __name__ == "__main__":
    
    argv = rospy.myargv()
    if len(argv) == 1:
        import random
        x = random.randint(-50000, 50000)
        y = random.randint(-50000, 50000)
    elif len(argv) == 3:
        try:
            x = int(argv[1])
            y = int(argv[2])
        except:
            print usage()
            sys.exit(1)
    else:
        print usage()
        sys.exit(1)
    print "%s + %s = %s"%(x, y, add_two_ints_client(x, y))

服务端

#!/usr/bin/env python

NAME = 'add_two_ints_server'

# import the AddTwoInts service
from beginner_tutorials.srv import *
import rospy 

def add_two_ints(req):
    print("Returning [%s + %s = %s]" % (req.a, req.b, (req.a + req.b)))
    sum = req.a + req.b
    return AddTwoIntsResponse(sum)

def add_two_ints_server():
    rospy.init_node(NAME)
    s = rospy.Service('add_two_ints', AddTwoInts, add_two_ints)
    print "Ready to add Two Ints"
    # spin() keeps Python from exiting until node is shutdown
    rospy.spin()

if __name__ == "__main__":
    add_two_ints_server()