Is there any API call to get IP Address of a machine? I know there is function which returns name of the machine, gethostname(). But I need the IP.

Thanks & Regards,
Ahsan

See gethostbyname()

Hey, could you all be a bit more specific on this one. I read the man page for gethostbyname and it seems to be returning a generic internal address format. That needs to be converted into a dot notation IP address, and I don't know how to do it.

Also, to extend this a bit, is it possible to obtain the information starting from a file descriptor that is a socket. I.E. if the only piece of information I have about the connection is the file descriptor, can I get the sockaddr_in structure from that to pass to gethostbyname to then convert into an IP?

Thanks!

The best solution to stuff like this is to browse some source code. There is a ton of source code on the internet. And there are several programs that format ip addresses. But I'm trapped at the office waiting for a tech, and I don't have anything better to do, so...

#ifdef __STDC__
#define PROTOTYPICAL
#endif
#ifdef __cplusplus
#define PROTOTYPICAL
#endif

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <netdb.h>
#include <arpa/inet.h>


#ifdef PROTOTYPICAL
int main(int argc, char *argv[])
#else
main(argc,argv)
char *argv[];
#endif
{
	char *mess;
	struct hostent *hp;
	int dumpall;

	dumpall=0;
	while(*++argv) {
		if(!strcmp(*argv,(char *)"-d")) {
			dumpall=!dumpall;
			continue;
		}
		/*
		 *  Call gethostbyname for current argument
		 */
		if(! (hp = gethostbyname(*argv))) {
			switch(h_errno){
					case HOST_NOT_FOUND:  
						mess=(char *)"Not Found";
						break;
					case TRY_AGAIN:  
						mess=(char *)"Time Out";
						break;
					case NO_RECOVERY:  
						mess=(char *)"No Recovery";
						break;
					case NO_ADDRESS:  
						mess=(char *)"No Address";
						break;
					default: 
						mess=(char *)"unknown error";
						break;
			}
			printf("%s  %s\n", *argv, mess);

		} else {
			printf("%s  %s  %s \n", *argv, hp->h_name,
				inet_ntoa(*(struct in_addr *)(hp->h_addr)));
			if(dumpall) {
				printf("  addresses:\n");
				while(*(hp->h_addr_list)){
					printf("      %s \n", 
						inet_ntoa(*(struct in_addr *)*(hp->h_addr_list)++));
				}
				printf("  aliases:\n");
				while(*(hp->h_aliases)){
					printf("      %s \n",*(hp->h_aliases)++);
				} 
			}
		}
	}
	exit(0);
}

Originally posted by DreamWarrior Also, to extend this a bit, is it possible to obtain the information starting from a file descriptor that is a socket. I.E. if the only piece of information I have about the connection is the file descriptor, can I get the sockaddr_in structure from that to pass to gethostbyname to then convert into an IP? Thanks!

Damn, the inet_ntoa won't work. I want to at least be able to get the IP after a call to accept on the socket.... I'll go searching, unless you all are bored and can help me out. If I find anything, I'll post it up...too bad no one around here as a good TCP for Unix book.

BTW, just out of curiosity, you're in Rockville and using HP-UX machines, any chance you're on an FAA contract?

Why won't inet_ntoa work? It seems to work whenever I try it. Post your code, maybe I or someone else will see something. And there are dozens of servers with source code available for you to find on the Internet. Most are able to log client ip addresses.

The best network programming book is UNIX Network Programming by Rich Stevens.

I will ignore your quest for additional clues to my identity.

it's so hard to read your source code.hehe.
What should I do for my first step of learning C network programming?
maybe it's not easy to answer.