[SOLVED] Segmentation fault during run time

chetan11 · 08-24-2011, 08:52 AM

I have compiled the below code successfully,
I have download this code from a site.
This code is related to client-server socket.
But when I run it, I got segmentation error.
Please anyone help.
Thanks

Code:

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

int main(int argc, char **argv)
{
	int sockfd,newsockfd;
	int c;
	char buf[100];
	struct sockaddr_in servaddr,cliaddr;
	
	sockfd=socket(AF_INET,SOCK_STREAM,0);

	servaddr.sin_family=AF_INET;
	servaddr.sin_addr.s_addr=htonl(INADDR_ANY);
	servaddr.sin_port=htons(atoi(argv[1]));

	bind(sockfd,(struct sockaddr *)&servaddr,sizeof(servaddr));

        listen(sockfd,5);//5 standsfor the max connections it can take.in linux 5 is for 8 connections.
	c=sizeof(cliaddr);
    	newsockfd=accept(sockfd,(struct sockaddr *)&cliaddr,&c);

	if(read(newsockfd,buf,100)<0)
		printf("Error Recv Data\n");
	else	
		printf("Server: Data Recvd\n");
	
	if(write(newsockfd,"Hello!!!",100)<0)
		printf("Error Sending Data\n");
	else
		printf("Server: Replying\n");
	return 0;
}

ta0kira · 08-24-2011, 09:55 AM

I'm assuming it happens at read or write and that accept fails because listen does, which fails because bind does. What port number are you using? Please rewrite your code to check the return values of socket, bind, listen, and accept. If any are -1, print out strerror(errno) and exit from the program. If you still get a segfault, compile with -g and run it with gdb.
Kevin Barry

dwhitney67 · 08-24-2011, 10:55 AM

Along with taOkira's advice, I also would recommend that you zero-out the servaddr structure before using it:

Code:

        ...
        memset(&servaddr, 0, sizeof(servaddr));

	servaddr.sin_family=AF_INET;
	servaddr.sin_addr.s_addr=htonl(INADDR_ANY);
	servaddr.sin_port=htons(atoi(argv[1]));

If you are running your application as a regular user, your port number must fall somewhere between 1024 and 65535. If you are running as root, then port numbers less than 1024 are available.

Check if bind() fails; it is does, it could indicate that the port you have chosen is already in use!