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Old 05-01-2004, 06:45 PM   #1
Registered: Oct 2002
Location: Ohio, USA
Distribution: OS X 10.4.8, Ubuntu 6.10
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sockaddr_in and sockaddr

Ok, I'm writing a simple client server program to do a CRC check on a file the client is going to send. Just one transfer and it's done.. So I set out and wrote them both almost at the same time (since they are similar with the exception of a few functions) and I get an error when I compiler the server in two places where I send a data type sockaddr_in to a function and then try to bind or accept (happens in both functions). Here is my program:

#include <iostream.h>
#include <sys/types.h>
#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <string.h>
#include <unistd.h>
#include <fstream.h>
#include <sys/param.h>
#include <stdlib.h>

#define PACKETSIZE 20
#define PORTNUM 39992

typedef enum {data, ack} servicetype;

typedef struct
	servicetype service;
	int sequence;
	int datasize;
	int last;
	char data[PACKETSIZE];
	int checksum;

struct sockaddr_in getHost()
	struct sockaddr_in sa;
	struct hostent * ph;
	char myname[MAXHOSTNAMELEN + 1];
	gethostname(myname, MAXHOSTNAMELEN);
	if((ph = gethostbyname(myname)) == NULL)
		cout << "gethosbyname has failed! Exiting..." << endl;
	memset(&sa, 0, sizeof(struct sockaddr_in));
	sa.sin_family = ph->h_addrtype;
	sa.sin_port = htons(PORTNUM);
	return sa;

int openSocket()
	int sock;
	if((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0)
		cout << "Error getting socket! Exiting..." << endl;
	return sock;

void bindAndListen(int sock, struct sockaddr_in sa)
	if(bind(sock, &sa, sizeof(sa)) < 0)  //Happens Here
		cout << "Bind failed! Exiting..." << endl;
	listen(sock, 5);

int acceptConnection(int sock)
	int sd;
	struct sockaddr_in sa;
	unsigned int saSize;
	saSize = sizeof(sa);
	if((sd = accept(sock, &sa, &saSize)) < 0)  //Add here!!
		cout << "Accept failed! Exiting..." << endl;
	cout << "Connection established with: " << sa.sin_addr.s_addr << endl;
	return sd;

void getFile(FILE * file, int sock)
	PACKET * packet;
	int x;
	packet = (PACKET *) malloc (sizeof(*packet));
		if(recv(sock, packet, sizeof(*packet), 0) <= 0)
			cout << "Error receiving file! Exiting..." << endl;
		cout << "Recieved Packet: " << packet->sequence << " " << packet->data << endl;
		for(x = 0; x < packet->datasize; x++)
			putc(packet->data[x], file);
		//if(packet->sequence % 5 == 4)
		// ACK
	} while(!packet->last);

typedef unsigned int Uint; //non negative int
typedef unsigned char Uchar;

//CRC table found online
Uint crc_table[] =
	0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
	0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440,
	0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40,
	0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841,
	0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40,
	0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41,
	0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641,
	0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040,
	0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,
	0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441,
	0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,
	0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840,
	0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41,
	0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40,
	0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640,
	0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041,
	0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240,
	0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,
	0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41,
	0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840,
	0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41,
	0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40,
	0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640,
	0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041,
	0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241,
	0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481, 0x5440,
	0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40,
	0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841,
	0x8801, 0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40,
	0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41,
	0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,
	0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040,

int main (int argc, char * const argv[])
	int sock, sockfd;
	struct sockaddr_in myAddr;
	FILE * file;
	int ch; 
	long crcIn = 0;
	Uint acc0 = 0xFFFF;
	myAddr = getHost();
	sock = openSocket();
	bindAndListen(sock, myAddr);
	sockfd = acceptConnection(sock);
	getFile(file, sock);
	//CRC stuff here
	//need to recieve CRC
	while((ch = getc(file)) != EOF)
		acc0 = crc_table[(Uchar) ch ^ (Uchar) acc0] ^ (Uchar) (acc0 >> 8); //calculate CRC
	cout << "CRC checksum is: " << std::hex << acc0 << "." << endl; //Print CRC
	cout << "Checking CRC for equality..." << endl;
	if (crcIn == (int)acc0)
		cout << "CRC check validated!" << endl;
	else if (crcIn != (int)acc0)
		cout << "CRC check Failed!" << endl;
	return 0;
here are the errors I recieve:

server.cpp: In function `void bindAndListen(int, sockaddr_in)':
server.cpp:66: type `const sockaddr' is not a base type for type `sockaddr_in'
server.cpp: In function `int acceptConnection(int)':
server.cpp:82: type `sockaddr' is not a base type for type `sockaddr_in'

Any help or explanation as to why this is happening would be awesome. I'm new to client/server programs but I'm trying Thanks!!

Old 05-01-2004, 07:25 PM   #2
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Location: Zurich, Switzerland
Distribution: Debian/unstable
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According to the man page (accept(2)), the struct is named as 'sockaddr', not 'sockaddr_in'.
Old 05-01-2004, 08:00 PM   #3
Registered: Mar 2004
Location: bursa
Posts: 110

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ToniT is right; you should be casting your sockaddr_in's to sockaddr's (that's just how it's done I believe; ie. bind and some other such functions take a struct sockaddr ).
Old 05-02-2004, 08:28 AM   #4
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Registered: Mar 2004
Location: germany
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Exactly correct.
And casting is a legal way here because all sockaddr_xxx structs are of identical size.

This is from sys/socket.h and shows the point where all the types go into one union.
/* This is the type we use for generic socket address arguments.

   With GCC 2.7 and later, the funky union causes redeclarations or
   uses with any of the listed types to be allowed without complaint.
   G++ 2.7 does not support transparent unions so there we want the
   old-style declaration, too.  */
#if defined __cplusplus || !__GNUC_PREREQ (2, 7) || !defined __USE_GNU
# define __SOCKADDR_ARG		struct sockaddr *__restrict
# define __CONST_SOCKADDR_ARG	__const struct sockaddr *
/* Add more `struct sockaddr_AF' types here as necessary.
   These are all the ones I found on NetBSD and Linux.  */
  __SOCKADDR_ONETYPE (sockaddr) \
  __SOCKADDR_ONETYPE (sockaddr_at) \
  __SOCKADDR_ONETYPE (sockaddr_ax25) \
  __SOCKADDR_ONETYPE (sockaddr_dl) \
  __SOCKADDR_ONETYPE (sockaddr_eon) \
  __SOCKADDR_ONETYPE (sockaddr_in) \
  __SOCKADDR_ONETYPE (sockaddr_in6) \
  __SOCKADDR_ONETYPE (sockaddr_inarp) \
  __SOCKADDR_ONETYPE (sockaddr_ipx) \
  __SOCKADDR_ONETYPE (sockaddr_iso) \
  __SOCKADDR_ONETYPE (sockaddr_ns) \
  __SOCKADDR_ONETYPE (sockaddr_un) \
  __SOCKADDR_ONETYPE (sockaddr_x25)

# define __SOCKADDR_ONETYPE(type) struct type *__restrict __##type##__;
typedef union { __SOCKADDR_ALLTYPES
	      } __SOCKADDR_ARG __attribute__ ((__transparent_union__));
# define __SOCKADDR_ONETYPE(type) __const struct type *__restrict __##type##__;
typedef union { __SOCKADDR_ALLTYPES
	      } __CONST_SOCKADDR_ARG __attribute__ ((__transparent_union__));

Old 05-02-2004, 03:52 PM   #5
Registered: Oct 2002
Location: Ohio, USA
Distribution: OS X 10.4.8, Ubuntu 6.10
Posts: 146

Original Poster
Rep: Reputation: 15
got it working. thanks a lot you guys! as always, you rock! :-)


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