openGL - issue when getting data via socket in glutTimerFunc - c++

Question

I am using UDP socket to send data to my openGL application. the openGL app should listent to the UDP socket in the glutTimerFunc callback and update the view according to the received data.
my main function:
int main(int argc, char* argv[])
{
glutInit(&argc, argv);
glutInitWindowSize(600, 600);
glutInitDisplayMode(GLUT_RGBA | GLUT_DEPTH | GLUT_DOUBLE);
glutCreateWindow("test");
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutTimerFunc(1000, listenToUDP, 0); // here!
glClearColor(0,0,0,1);
glutMainLoop();
return 0;
}
my glutTimerFunc callback, which listens to the UDP socket:
void listenToUDP(int = 0)
{
int sockfd,n;
struct sockaddr_in servaddr,cliaddr;
socklen_t len;
char mesg[1000];
sockfd=socket(AF_INET,SOCK_DGRAM,0);
bzero(&servaddr,sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr=htonl(INADDR_ANY);
servaddr.sin_port=htons(32000);
bind(sockfd,(struct sockaddr *)&servaddr,sizeof(servaddr));
len = sizeof(cliaddr);
printf("1");
// here is the problem !!
n = recvfrom(sockfd,mesg,1000,0,(struct sockaddr *)&cliaddr,&len);
printf("2");
sendto(sockfd,mesg,n,0,(struct sockaddr *)&cliaddr,sizeof(cliaddr));
printf("-------------------------------------------------------\n");
mesg[n] = 0;
printf("Received the following:\n");
printf("%s",mesg);
printf("-------------------------------------------------------\n");
map<string, float> info = parseInfo(mesg);
scaleX += info.find("x") -> second;
printf("%f", scaleX);
glutPostRedisplay();
glutTimerFunc(1000, listenToUDP, 0);
}
when the first time I sent data to the application, it worked great. it waited for the data on the line I marked, and it printed everything and updated the view accordingly after I sent data to it.
However, it didn't work since the second time I sent data to it. it would print "1" but never print "2", which means it suspended on the line I marked. of course it would not update the view, either.
I am sure the UDP listener works well if it's independent(run it with an infinite loop), so I guess it's a problem related to the glutTimerFun. However, I totally have no idea.
my question is:
1) what's the reason for this behavior?
2) how can I fix it?

Answer 1

Please use & operator to get the address of function.
glutTimerFunc(1000, &listenToUDP, 0);
Please also remember to close the socket after using it every time:
close(sockfd);