Hi Experts,

I'm writing a C program (cut/paste below) to establish a TCP socket connection from my Mac Pro to a Windows XP-based test instrument sitting next to it over LAN (Ethernet). The program compiles without any warnings or errors. But executing the code using GNU Debugger, I can see it exits at 'exit(2)' which is the "if(connect(MySocket" line. There's no timeout, it just exits immediately.

I compile using:
gcc -g -Wall talk2me.c -o talk2me
but I don't get any hints in the output nor when debugging at to what might be the issue.

I'm sure the and port 5025 are correct (independently, using Matlab code I can communicate fine using these parameters). Any idea where else I could look to debug?

Outside of the code itself, are there any other requirements (perhaps system-level) that need to be satisfied (like running the code from a certain directory, or setting a parameter in unix to allow connections, etc.)? It may be something obvious that I'm missing as I'm not that experienced in this.

I can run a 'hello world' program fine, it that helps.


#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/tcp.h>
#include <netinet/in.h>
#include <arpa/inet.h> 		//for inet_addr
#include <unistd.h> 		// for function 'close'

int main(void)
int MySocket;
if((MySocket=socket(PF_INET,SOCK_STREAM,0))==-1) exit(1);

struct in_addr {
	unsigned long s_addr;
struct sockaddr_in {
	short int sin_family; 			// Address family
	unsigned short int sin_port; 	// Port number
	struct in_addr sin_addr; 		// Internet address
	unsigned char sin_zero[8]; 		// Padding
struct sockaddr_in MyAddress;

// Initialize the whole structure to zero
memset(&MyAddress,0,sizeof(struct sockaddr_in));
// Then set the individual fields
MyAddress.sin_family=PF_INET; 		// IPv4
MyAddress.sin_port=htons(5025); 	// Port number used by instrument
MyAddress.sin_addr.s_addr=inet_addr(""); // IP Address

if(connect(MySocket,(struct sockaddr *) &MyAddress, 
	sizeof(struct sockaddr_in))==-1) exit(2);  
// Send SCPI command
if(send(MySocket,"*IDN?\n",6,0)==-1) exit(3);

// Read response
char buffer[200];
int actual;
if((actual=recv(MySocket,&buffer[0],200,0))==-1) exit(4);
buffer[actual]=0; // Add zero character (C string)
printf("Instrument ID: %s\n",buffer);

// Close socket
if(close(MySocket)==-1) exit(99);

return 0;

It's solved now. I just needed to comment out the struct's for in_addr and sockaddr_in, which apparantly are defined in <netinet/in.h>.