simple TCP client serve model in C : client not recieving - c

Question

im making a simple TCP client-server in c and im trying to send a message from the client to the server, but im having some problems with it.
The server does send the message (integer value > 0) but the client is unable to receive it (integer value > 0)
here is the code:
Client
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <stdio.h>
int main()
{
int s_id;
char *msg = "hello";
struct sockaddr_in serv_addr;
s_id = socket (AF_INET, SOCK_STREAM, 0);
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons (1156);
serv_addr.sin_addr.s_addr = inet_addr("127.0.0.1");
connect(s_id,(struct sockaddr *) &serv_addr, sizeof (struct sockaddr));
int r = recv (s_id, (char *) msg, 9, 0);
printf("%d \n", r );
printf("%s \n", msg );
return 0;
}
Server:
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
int main()
{
int s_id;
char *msg = "connected";
struct sockaddr_in my_addr, remote_addr;
s_id = socket (PF_INET,SOCK_STREAM,0);
my_addr.sin_family = AF_INET;
my_addr.sin_port = htons(1156);
my_addr.sin_addr.s_addr = inet_addr("127.0.0.1");
bind(s_id,(struct sockaddr *) &my_addr, sizeof(struct sockaddr));
listen (s_id,5);
int size = sizeof (struct sockaddr_in);
int new_sd = accept (s_id, (struct sockaddr *) &remote_addr, &size);
int s= send(new_sd, (void *)msg, 9, 0);
printf("%d \n", s );
return 0;
}
The outputs i get (after first starting the server, and then the client) are
server side: 9
client-side: -1
hello
I am using Ubuntu 11.04 and the gcc compiler.
I hope someone out there can help.
Thank you
Umar

Answer 1

char *msg = "hello";
This is a string literal. It's a constant, and you can't change it.
int r = recv (s_id, (char *) msg, 9, 0);
And there you're trying to write to it.
Change your declaration to:
char msg[20];
memset(msg, 0, sizeof(msg));
If you make that change, your code works as expected.
In C you're going to have to allocate and manage buffers - there's no free lunch :)
Also take note of the other answer from Nikolai N Fetissov - you really should be checking return codes from all the system calls.

Answer 2

You never check for errors after any of the system calls. All of socket(2), connect(2), etc. return -1 on failure, then you can print the error description with, say, perror(3) function. Each system call manual page lists possible errors.
Edit 0:
The real problem is probably what Brian points out - you are trying to receive data into read-only memory on the client. Does it die with a segfault?