在Ubuntu18.0里用Rosrun运行下列代码时，总是报错“行四未预期的符号'('附近有语法错误，请问这是为什么？
```c++
#include "ros/ros.h"
#include "chapter2/chapter2_srv1.h" //包含我们创建的srv文件
bool add(chapter2::chapter2_srv1::Request &req, chapter2::chapter2_srv1::Response &res) //服务变量
{
res.sum = req.A + req.B + req.C;
ROS_INFO("request: A=%d, B=%d C=%d", (int)req.A, (int)req.B, (int)req.C);//请求输入
ROS_INFO("sending back response: [%d]", (int)res.sum); //输出
return true;
}
//这个函数会对3个变量求和，并将计算结果发送给其他节点
int main(int argc, char **argv)
{
ros::init(argc, argv, "add_3_ints_server");
ros::NodeHandle n;
ros::ServiceServer service = n.advertiseService("add_3_ints", add); //创建服务并发布广播
ROS_INFO("Ready to add 3 ints.");
ros::spin();
return 0;
}
```
