Thread: Socket Programming Help

Hi im trying to write client code for UDP Socket Programming and havin trouble trying to receive a msg and get it back into a struct. the Errors i'm getting are:

UDPclient.c:171: error: request for member ‘err’ in something not a structure or union
UDPclient.c:175: error: request for member ‘errStr’ in something not a structure or union
UDPclient.c:178: error: request for member ‘x’ in something not a structure or union
UDPclient.c:179: error: request for member ‘y’ in something not a structure or union
UDPclient.c:180: error: request for member ‘temp’ in something not a structure or union
UDPclient.c:181: error: request for member ‘tLeft’ in something not a structure or union
UDPclient.c:182: error: request for member ‘mLeft’ in something not a structure or union
UDPclient.c:202: error: request for member ‘mLeft’ in something not a structure or union
UDPclient.c:203: error: request for member ‘tLeft’ in something not a structure or union

these are towards the bottom of the code in the receiving response section of the code

Code:

#include <stdio.h>      
#include <sys/socket.h> /* for socket(), connect(), sendto(), and recvfrom() */
#include <arpa/inet.h>  /* for sockaddr_in and inet_addr() */
#include <stdlib.h>     /* for atoi() and exit() */
#include <string.h>     /* for memset() */
#include <unistd.h>     /* for close() */
#include <strings.h>
#include <time.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <math.h>
#include <errno.h>
#include <assert.h>

#define ECHOMAX 255     /* Longest string to echo */

#define SERV_PORT    31180      /* server UDP port */
#define SERV_IP		 "149.171.37.233" /* server IP Address */
#define GRID_SIZE    100        /* 100 x 100 grid */
#define PASSWD       "thunt10"  /* password in each packet */

#define MAX_MSG_LEN  64        /* max size of any msg */
#define MAX_TIME     120       /* time (seconds) limit for a game */
#define MAX_MOVES    100       /* mximum number of moves allowed */

#define MSG_REGISTER    1
#define MSG_MOVE        2

typedef struct {
  char passwd[8];              /* password */
  unsigned long mType;         /* message type = MSG_REGISTER */
  unsigned long id;            /* student id */
  unsigned short x, y;         /* x and y co-ordinates of starting point */
} RegMsg_t;

typedef struct {
  char passwd[8];              /* password */
  unsigned long mType;         /* message type = MSG_MOVE */
  unsigned long id;            /* student id */
  char dir;                    /* direction: N, S, E, or W */
  char pad[3];                 /* padding for word-alignment */
} MoveMsg_t;

typedef struct {
  unsigned long err;           /* error code: 0 if all ok */
  unsigned short x, y;         /* x and y co-ordinates of current location */
  long temp;                   /* temperature */
  unsigned long tLeft;         /* time left */
  unsigned long mLeft;         /* moves left */
  char errStr[108];            /* error string */
} RespMsg_t;

int main(int argc, char *argv[]) {
	int sock;                        /* Socket descriptor */
	int e;
	long err;
	int inMsgLen;
	//int outMsgLen;

	char passwd[8];
	long temp, tleft, mleft;
	unsigned short x, y;
	unsigned long mType, id;

	//long ttaken, mtaken;

	//char dir;
	//char pad[3];

	char inMsg[MAX_MSG_LEN];
	//char outMsg[MAX_MSG_LEN];

    struct sockaddr_in servAddr;	 /* Echo server address */
    struct sockaddr_in fromAddr;     /* Source address of echo */

	RegMsg_t regmsg;			 	 /* Registration Message */
	RespMsg_t *respmsg;				 /* Response Message from the Server */
	//MoveMsg_t movmsg;				 /* Move Message */

    //unsigned short echoServPort;     /* Echo server port */
 
    unsigned int fromSize;           /* In-out of address size for recvfrom() */

	unsigned short servPort = 31180; /* Server UDP port number */

    char *servIP = "149.171.37.233"; /* IP address of server */

    //char *echoString;                /* String to send to echo server */
    //char echoBuffer[ECHOMAX+1];      /* Buffer for receiving echoed string */

	int regmsgLen;					 /* Length of Registration message */

    //int echoStringLen;               /* Length of string to echo */

    //int respStringLen;               /* Length of received response */



	/* GETTING REGISTER-MESSAGE PACKAGED & SENT */
    if ((argc < 5) || (argc > 6)) {	  /* Test for correct number of arguments */
    	printf("Please enter <password> <message-type> <student-id> <x-location> <y-location>\n");

        exit(1);
    }

	/* Scanning data from user input */
	strcpy(passwd, argv[1]);    /* First arg: password "thunt10" */
	mType = atoi(argv[2]);		/* Second arg: message-type */
	id = atoi(argv[3]);			/* Third arg: student-id */
	x = atoi(argv[4]);			/* Fourth arg: x-coordinate */
	y = atoi(argv[5]);			/* Fifth arg: y-coordinate */

    //servIP = argv[1];
    //echoString = argv[2];

	regmsgLen = sizeof(regmsg);

    //if ((echoStringLen = strlen(echoString)) > ECHOMAX)  /* Check input length */
        //printf("Echo word too long");

    //if (argc == 4)
        //echoServPort = atoi(argv[3]);  /* Use given port, if any */
    //else
        //echoServPort = 7;  /* 7 is the well-known port for the echo service */
	
    /* Create a datagram/UDP socket */
    if ((sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0) {
        printf("socket() failed");
	}

    /* Construct the server address structure */
    memset(&servAddr, 0, sizeof(servAddr));    		/* Zero out structure */
    servAddr.sin_family = AF_INET;                 	/* Internet addr family */
    servAddr.sin_addr.s_addr = inet_addr(servIP);   /* Server IP address */
    servAddr.sin_port   = htons(servPort);     		/* Server port */

	memset(&regmsg, 0, regmsgLen);
	strcpy(regmsg.passwd, passwd);
	regmsg.mType = htonl(mType);
	regmsg.id = htonl(mType);
	regmsg.x = htons(x);
	regmsg.y = htons(y); 

    /* Send the string to the server */
    if ((e = sendto(sock, (char *)&regmsg, regmsgLen, 0, (struct sockaddr *)&servAddr, sizeof(servAddr))) != regmsgLen) {
        printf("sendto() sent a different number of bytes than expected");
	}
  	else if (e < 0) {
		printf("Error with sending\n");
		exit(1);
	}


    /* RECEIVING A RESPONSE MESSAGE AFTER REGISTRATION */
    fromSize = sizeof(fromAddr);
    inMsgLen = recvfrom(sock, inMsg, MAX_MSG_LEN, 0, (struct sockaddr *)&fromAddr, &fromSize);

    if (servAddr.sin_addr.s_addr != fromAddr.sin_addr.s_addr) {
        fprintf(stderr,"Error: received a packet from unknown source.\n");
        exit(1);
    }

	respmsg = (RespMsg_t *)inMsg;
	err = ntohl(respmsg.err);

	if (err != 0) {
        printf("Registration failed.\n");
		printf("%s\n", respmsg.errStr);
	}
	else {
		x = ntohs(respmsg.x);
		y = ntohs(respmsg.y);
		temp = ntohl(respmsg.temp);
		tleft = ntohl(respmsg.tLeft);
		mleft = ntohl(respmsg.mLeft);

		printf("SERVER RESPONSE:\n");
		printf("x-location = %d\ty-location = %d\n", x, y);
		printf("temperature = %ld\n", temp);
		printf("time-left = %ld\n", tleft);
		printf("moves-left = %ld\n", mleft);
	}

You are using DOT thats causing you problem. Since you created "respmsg" dynamically. So you'd need "->" to use its members.

thanks buddy

so whats the general rule for '->' or '.'

sorry not really sure what u mean by dynamic

Well I would suggest to read your book.
For pointers (*) they are allocated at run time i.e. dynamically. We use "->" for it.