actionlib client question

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Hi all, I want to use actionlib to send gripping control cmd to gripper_controller(arbotix package), but after compiling I ran my node, and get strange info: "terminate called after throwing an instance of 'ros::InvalidNameException' what(): Using ~ names with NodeHandle methods is not allowed. If you want to use private names with the NodeHandle interface, construct a NodeHandle using a private name as its namespace. e.g. ros::NodeHandle nh("~"); nh.getParam("my_private_name"); (name = [~gripper_action]) Aborted (core dumped)"

I cannot change my code as the note's "nh.getParam("my_private_name")" because I need sentence like "GripperMoveClient ac("~gripper_action",true);" to define my client.

Pls help me, thanks! Below is my actionlib client code.

#include ros/ros.h>  //in order to show for you I //deliberately lose "<"

#include actionlib/client/simple_action_client.h>

#include control_msgs/GripperCommandAction.h>

typedef actionlib::SimpleActionClient<control_msgs::GripperCommandAction> GripperMoveClient;

int main(int argc, char** argv){

ros::init(argc, argv, "grasping_points_node");

GripperMoveClient ac("~gripper_action",true);

 while(!ac.waitForServer(ros::Duration(5.0))){

  ROS_INFO("Waiting...");}

  control_msgs::GripperCommandGoal goal;

  goal.command.position=0.01;

  ac.sendGoal(goal);

}