Server Socket

I'm trying to write a simple C server program using sockets, that will interract with a Java client - I've never used BSD sockets before, so I'm a bit lost. I've written the program how, from what I've seen, I'm supposed to, but it won't compile. I've attached the code below:#include <stdio.h>#include <sys/types.h>#include <sys/socket.h>#include <unistd.h>#include <netinet/in.h>int main(){int sock = 0;struct sockaddr_in address;address.sin_family = AF_INET;address.sin_addr.s_addr = INADDR_ANY;address.sin_port = htons(9001);sock = socket(PF_INET, SOCK_STREAM, 0);if (sock == -1)printf("Error creating socket");else{if (bind(sock, (struct sockaddr *)& address, sizeof(address)))printf("error binding socket");else{printf("socket bound successfully");listen(sock,5);struct sockaddr_in address2;int addrlen = sizeof(struct sockaddr_in);int newSocket = accept(sock, (struct sockaddr *)&address2, &addrlen);if (newSocket < 0)printf("Error accepting incoming connection\n");else{char* msg = "Test message";printf("About to send the message");send(sock,msg,strlen(msg),0);printf("I think i just sent the message");}} }close(sock);return 0;}but when I attempt to compile I'm getting the errors below:$ gcc servtest.cUndefined first referencedsymbol in filebind /var/tmp//cc3taE90.osend /var/tmp//cc3taE90.oaccept /var/tmp//cc3taE90.olisten /var/tmp//cc3taE90.osocket /var/tmp//cc3taE90.old: fatal: Symbol referencing errors. No output written to a.outcollect2: ld returned 1 exit statusAny ideas anybody???

I had to move some of the variables out of your inner if/else statements to declare them at the beginning to get it to compile. It seems odd. The code seems correct (I've done server building before, so you've got all the headers, and all the function calls should work).Maybe instead of nesting the if/else just call function, test for error, exit(1) upon errors, otherwise continue.And you could always try using perror() to display error messages. I've always found it to be more useful than printing what I think has gone wrong. Anyway, tell us how you go.

This is the part where I had problems compiling:

 

struct sockaddr_in address2;int addrlen = sizeof(struct sockaddr_in);int newSocket = accept(sock, (struct sockaddr *)&address2, &addrlen);

For some reason, it didn't like the variables being declared at that point in the code.

 

Instead, I had

 

int main(){  ... // initial variable declarations at beginning  int addrlen = sizeof(struct sockaddr_in);  struct sockaddr_in address2;  int newSocket;  ... // some code...  accept(sock, (struct sockaddr *)&address2, &addrlen);  ... // some more code  return(0);}

Another thing you should always do (at least, it's recommended, anyway), is to zero out the rest of the sockaddr_in struct.

 

struct sockaddr_in address;address.sin_family = AF_INET;address.sin_addr.s_addr = INADDR_ANY;address.sin_port = htons(9001);memset(&(address.sin_zero), '\0', 8);

Last of all, if your server is shutdown, and you try to start it again, you'll often have problems binding again.

 

And lastly, remember to use the

 tags for your code.

Another thing. I must've been on drugs when I said don't nest the ifs. If it's formatted right, it does look much nicer. I've just been modifying my server to be an object, and I've broken socket() and check, setsockopt() and check, bind() and check, etc.. into small functions. Only small functions, but it get rid of all the nasty fail checking in the main calling function (actually, they're all placed into another startup function, too). The point was, nest away if you feel like it, it doesn't really matter either way.One last thing... have you had any results? There's been so many questions, but no actual response to see if anything we've said actually helped. I'm sure I'm not the only one who wants to get a bit of feedback.