server recieving some junk value from the client? - c

Question

#include <windows.h>
#include <stdio.h>
#include <string.h>
#include <winsock.h>
#pragma once
#pragma comment (lib, "ws2_32.lib")
#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>
#include <time.h>
#include <winsock.h>
#include <io.h>
SOCKET sock;
SOCKET fd;
char recv_data[10];
int port = 18001;
void CreateSocket()
{
struct sockaddr_in server, client; // creating a socket address structure: structure contains ip address and port number
printf("Initializing Winsock\n");
WORD wVersionRequested;
WSADATA wsaData;
wVersionRequested = MAKEWORD (1, 1);
if (WSAStartup (wVersionRequested, &wsaData) != 0){
printf("Winsock initialised failed \n");
} else {
printf("Initialised\n");
}
// create socket
sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (sock < 0) {
printf("Could not Create Socket\n");
//return 0;
}
printf("Socket Created\n");
// create socket address of the server
memset( &server, 0, sizeof(server));
// IPv4 - connection
server.sin_family = AF_INET;
// accept connections from any ip adress
server.sin_addr.s_addr = htonl(INADDR_ANY);
// set port
server.sin_port = htons(port);
//Binding between the socket and ip address
if(bind (sock, (struct sockaddr *) &server, sizeof(server)) < 0)
{
printf("Bind failed with error code: %d", WSAGetLastError());
}
//Listen to incoming connections
if(listen(sock,3) == -1){
printf("Listen failed with error code: %d", WSAGetLastError());
}
printf("Server has been successfully set up - Waiting for incoming connections");
int len;
len = sizeof(client);
fd = accept(sock, (struct sockaddr*) &client, &len);
if (fd < 0){
printf("Accept failed");
}
//echo(fd);
printf("\n Process incoming connection from (%s , %d)", inet_ntoa(client.sin_addr),ntohs(client.sin_port));
//closesocket(fd);
}
int main()
{
CreateSocket();
while(1)
{
if(fd == -1)
{
printf("socket error\n");
}
else
{
recv(fd, recv_data, 9, 0);
printf("value is %s", recv_data);
}
}
return 0;
}
The above is a server code : I am creating a socket and accepting the data from the client. The client is sending a data and the server is accepting it.
If the client sends a to the server then the server will add some junk characters to it. If the client sends 4 characters then it will receive all the four characters. if the client sends one or two characters :Why the server is receiving some junk value ??

Answer 1

This is because, recv does not append NULL character at the end of the string. You have to explicitly add the NULL character. So, use return value of recv call and use it to append the NULL character.
int retval;
retval = recv(fd, recv_data, 9, 0);
if(retval != SOCKET_ERROR) {
recv_data[retval] = '\0';
printf("value is %s", recv_data);
}

Answer 2

'\0' is the only character which will differ you from char array and string.
Since you are using %s to print the string it is necessary to add the '\0' character at the end.