Question

I want to establish connection between two pc using client and server using C
I have been able to sent data from client and receive by server.
but when server want to sent data the error are appear in server side:
segmentation fail :11

here my program:
in client:

#include <stdio.h> 
#include <stdlib.h> 
#include <unistd.h> 
#include <errno.h> 
#include <string.h> 
#include <sys/types.h> 
#include <sys/socket.h> 
#include <netinet/in.h> 
#include <arpa/inet.h> 
#include <netdb.h>
#define MYPORT 4950
#define MAXBUFLEN 100 

int main() {
    char no[16], dt[30];
    printf("‐‐‐‐‐ PROGRAM CHATTING ‐‐‐‐‐\n");
    printf("To : ");
    scanf("%s", no);
    while(1){
        printf("Me : ");
        scanf("%s", dt); send(no, dt); receive();
   } 
} 

int send(char no[], char dt[])
{
int sockfd;
struct sockaddr_in my_addr;
struct sockaddr_in their_addr; 
struct hostent *he;

int addr_len, numbytes;
if((he = gethostbyname(no)) == NULL) 
{
    perror("gethostbyname");
    exit(1); 
}
if((sockfd=socket(AF_INET,SOCK_DGRAM,0))==-1)
{ //40
    perror("socket");
    exit(1); 
}
their_addr.sin_family = AF_INET;

their_addr.sin_port = htons(MYPORT); 
their_addr.sin_addr=*((struct in_addr*)he->h_addr);
memset(&(their_addr.sin_zero), '\0', 8);
if((numbytes=sendto(sockfd,dt,strlen(dt),0,(struct sockaddr*)&their_addr,sizeof(struct sockaddr)))==-1)
    {
    perror("sendto");
    exit(1); 
}
close(sockfd);
return 0; 
}

int receive()
{
     int sockfd;

struct sockaddr_in my_addr; 
struct sockaddr_in their_addr; 
struct hostent *he;

int addr_len, numbytes;
char buf[MAXBUFLEN];
if((sockfd=socket(AF_INET,SOCK_DGRAM,0))==-1) //68
{
    perror("socket");
    exit(1); 
}
my_addr.sin_family = AF_INET; 
my_addr.sin_port = htons(MYPORT); 
my_addr.sin_addr.s_addr = INADDR_ANY; memset(&(my_addr.sin_zero),'\0',8);
if(bind(sockfd,(struct sockaddr *)&my_addr,sizeof(struct sockaddr))==-1)
{
    perror("bind");
    exit(1); 
}
addr_len = sizeof(struct sockaddr);
if((numbytes=recvfrom(sockfd,buf,MAXBUFLEN-1,0,(struct sockaddr *)&their_addr,&addr_len))==-1)
{
    perror("recvfrom");
    exit(1); }
buf[numbytes]='\0';

printf("%s : \"%s\"\n", inet_ntoa(their_addr.sin_addr), buf);
close(sockfd);
return 0; 
}

and server:

 #include <stdio.h> 
 #include <stdlib.h> 
 #include <unistd.h> 
 #include <errno.h> 
 #include <string.h> 
 #include <sys/types.h> 
 #include <sys/socket.h> 
 #include <netinet/in.h> 
 #include <arpa/inet.h> 
 #include <netdb.h>
 #define MYPORT 4950
 #define MAXBUFLEN 100
char noip[50]; 
int main() 
{
char no[16];
char dt[30];
printf("‐‐‐‐‐ PROGRAM CHATTING ‐‐‐‐‐\n");
receive();
strcpy (no, noip); 
while(1){
    printf("Me : ");
    scanf("%s", dt); 
    send( dt); 
    receive();
    }
 } 

 int send(char dt[30]) {
   int sockfd;
   struct sockaddr_in my_addr; 
   struct sockaddr_in their_addr; 
   struct hostent *he;
   int addr_len, numbytes;

if((sockfd=socket(AF_INET,SOCK_DGRAM,0))==-1){
        perror("socket");
        exit(1); 
    }
    their_addr.sin_family = AF_INET;
    their_addr.sin_port = htons(MYPORT); 
their_addr.sin_addr=*((struct in_addr*)he->h_addr);
memset(&(their_addr.sin_zero), '\0', 8);
if((numbytes=sendto(sockfd,dt,strlen(dt),0,(struct sockaddr *)&their_addr,sizeof(struct sockaddr)))==-1)        
        {
        perror("sendto");
        exit(1); }
    close(sockfd);
    return 0; }

int receive() {
int sockfd;
struct sockaddr_in my_addr;
struct sockaddr_in their_addr; 
struct hostent *he;
int addr_len, numbytes;
char buf[MAXBUFLEN];
char no[16];

if((sockfd=socket(AF_INET,SOCK_DGRAM,0))==-1){
        perror("socket");
        exit(1); }

my_addr.sin_family = AF_INET; 
my_addr.sin_port = htons(MYPORT); 
my_addr.sin_addr.s_addr = INADDR_ANY; 
memset(&(my_addr.sin_zero),'\0',8);

if(bind(sockfd,(struct sockaddr *)&my_addr,sizeof(struct sockaddr))==-1){
        perror("bind");
        exit(1); }

addr_len = sizeof(struct sockaddr);
if((numbytes=recvfrom(sockfd,buf,MAXBUFLEN-1,0,(struct sockaddr *)&their_addr,&addr_len))==-1)
{
    perror("recvfrom");
    exit(1);}

buf[numbytes]='\0';
printf("%s : \"%s\"\n", inet_ntoa(their_addr.sin_addr), buf);
strcpy(no,inet_ntoa(their_addr.sin_addr));//copy data ke varibel no 
        close(sockfd);
        return 0;
}

Any sugestion?

Answer 1

Do a debug build (option -g) and then call the gdb. It opens a prompt where you use

file "a.out"

to load the executable and afterwards call “run” to actually run you program under debugger’s control. When the segfault happens, call “backtrace” and it should tell you the function and maybe the line where it happens.

But when I see the code, my first guess would be the input char array. Do you enter more than 29 characters when sending? 😉