Thread: Network Programming C / C++ question..

Hey guys, I'm really new to network programming and cant seem to get this program to work.

#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define DEST_IP "10.12.110.57"
#define DEST_PORT 23

main()
{
int sockfd;
struct sockaddr_in dest_addr; // will hold the destination addr

sockfd = socket(PF_INET, SOCK_STREAM, 0); // do some error checking!

dest_addr.sin_family = AF_INET; // host byte order
dest_addr.sin_port = htons(DEST_PORT); // short, network byte order
dest_addr.sin_addr.s_addr = inet_addr(DEST_IP);
memset(&(dest_addr.sin_zero), '\0', 8); // zero the rest of the struct

// don't forget to error check the connect()!
connect(sockfd, (struct sockaddr *)&dest_addr, sizeof(struct sockaddr));
}

I tried writing this into pico, on a UNIX server at school and used a gcc compiler. I get the following error:


Undefined First referenced
symbol in file
__xnet_connect /var/tmp//ccC0mTbw.o
__xnet_socket /var/tmp//ccC0mTbw.o
__gxxpersonality_v0 /var/tmp//ccC0mTbw.o
inet_addr /var/tmp//ccC0mTbw.o
id: fatal: Symbol referencing errors. No output written to a.out
collect2: ld returned 1 exit status



I'm really not sure what I'm doing wrong here. btw, this is directly writen from http://beej.us/guide/bgnet/output/html/syscalls.html ... I'm not taking credit for this persons work, just my way of learning is retyping it myself while explaining it to myself. Any help on why this isn't working would be great.

Love forums!

am I not already linked to the correct header files?

... could you please elaborate? I'm still confused.

thanks

thanks salem,

I compiled it through

g++ -o server ntwk.cpp -lnsl -lsocket -lresolv

and it seems to have worked.

But, being a rather large newbie to this I am confused on if it really worked or not. There is a new file in my directory called "server" which I assume is the program in an executable form of some type?

If I type "server" and press enter, nothing happens. I added a simple printf command to let me know the program is running, and even still, when I type in server.. nothing happens. I must have done something wrong?

btw.. I think the school server is linux ;\

ahh Salem, thankyou very much. I have gotten the program to work and although it doesn't connect to my computer I know its compiled! You are indeed God of the C :P

Hi.

It sounds like you ran into a path issue. Under Linux (and other UN*X's) the current directory (named '.') is not explicitly in your path unless you set your $PATH environment variable to include '.'.

As a result, when you ran 'server' it was loading and running another application that happened to also be called 'server'. By using './server' you are specifically loading the app in your current directory.

Steve

Hi.

I'm curious (though not challenging) why that in itself would be a security risk. Is the concern that you could 'replace' a system command that gets called through a script somewhere with a malicios one?

Steve