c - recvfrom() is stuck and I don't know why -


i have project school. goal create ping program use echo service (c programming). echo service runs on udp port 7 , have activated simple tcp/ip. echo supposed reply message if gets one. here code made:

// ping.cpp : entry point  #include "ping.h" #pragma comment(lib,"ws2_32") //library   int main(int argc, char *argv[]) {      //variable     char ipadress[] = "127.0.0.1";     word versionprotocolesocket;     socket pingsocket;     struct sockaddr_in destination;     char packet[max_packet_size], reply[max_packet_size];     int err, msglength;      //initialisation of windows socket     printf("initialising wsa 2.2...\n");     versionprotocolesocket = makeword(2, 2);     err = initialisesocket(versionprotocolesocket);     if (err != 0) {         errsocket(err);         printf("the program stop\n");         _getch();         return exit_failure;     }     else         printf("initialisation success\n\n");      //socket creation     printf("socket creation...\n");     if ((pingsocket = socket(af_inet, sock_dgram, ipproto_udp)) == socket_error) {         printf("can't create socket\nthe program going stop\n");         _getch();         return exit_failure;     }     else         printf("creation sucess\n\n");      //préparation des variables pour l'utilisation de la fonction sendto()     destination.sin_family = af_inet;     destination.sin_port = htons(7);     destination.sin_addr.s_addr = inet_addr(adresseip);     msglength = sizeof(message);     int addrsize = sizeof(destination);      //beginning of ping     (int = 0; < 5; i++)     {         //sending         if (sendto(pingsocket, message, messagelength, 0, (struct sockaddr *)&destination, addrsize) == socket_error)             printf("can't send message : %d\n", wsagetlasterror());         else             printf("message %d sent\n", i);         //reception         if (recvfrom(pingsocket, reply, max_packet_size, 0, null, null) == socket_error)             printf("error : %d\n", wsagetlasterror());         else             printf("message %d received\n", i);     }       _getch();     return exit_success; }  int initialisersocket(word version) {     wsadata wsadata;     int err = wsastartup(version, &wsadata);     return err; }  void errsocket(int err) {     switch (err) {     case wsasysnotready:         printf("system not ready\n");         break;     case wsavernotsupported:         printf("unsuported protocol version\n");         break;     case wsaeinprogress:         printf("a version running\n");         break;     case wsaeproclim:         printf("max task reached\n");         break;     case wsaefault:         printf("pointer lpwsadata not valid\n");         break;     default:         printf("unknown error\n");         break;     } }

now ping.h code :

#pragma once #include "stdio.h" #include "winsock2.h" #include "conio.h" #include "stdint.h"  int initialisesocket(word version); void errsocket(int err);  #define max_packet_size 10*1024

the problem program stuck on recvfrom function , have no idea why. can explain?

you have no socket listening packets. need bind receiving socket address , port want use.

also note udp not guarantee delivery. if nothing listening packet, thrown away. need listening before send packet. obviously, presents problem in single thread. typically, have 2 separate processes (either different programs or created forking). 1 process create socket , listen on port , other create socket , send data.


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