netdb.h File Reference

struct  hostent {
        char    *h_name;        // official name of host
        char    **h_aliases;    // alias list 
        int     h_addrtype;     // host address type 
        int     h_length;       // length of address 
        char    **h_addr_list;  // list of addresses from name server 
};
#define h_addr  h_addr_list[0]  //address, for backward compatibility

h_name  Official name of the host.  
h_aliases  A NULL -terminated array of alternate names for the host.  
h_addrtype  The type of address being returned; usually AF_INET.  
h_length  The length, in bytes, of the address.  
h_addr_list  A NULL -terminated array of network addresses for the host. Host addresses are returned in network byte order.  
h_addr  The first address in h_addr_list; this is for backward compatibility.  

#include<stdio.h>
#include<arpa/inet.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <string.h>
Int main()
{
struct hostent *hp = 0;
char *test_url=www.google.com:
hp = gethostbyname(test_url);
if(hp==NULL)
printf("gethostbyname failed"):
else
printf("gethostbyname passed");
return 0;
}

Gethostbyname passed

#include<stdio.h>
#include<arpa/inet.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <string.h>
#define urlsize 50
Int main()
{
struct hostent *hp = 0;
char addr[256];
unsigned long  test_addr;
strcpy(addr," 147.243.3.83");
test_addr=inet_addr(addr);
struct hostent *hp;
hp=gethostbyaddr((const char *)&test;_addr,sizeof(test_addr),AF_INET);
if(hp)
printf("DNS query resolved");
else
printf("gethostbyaddr failed");
return 0;
}

struct  protoent {
        char    *p_name;        /* official name of protocol */
        char    **p_aliases;    /* alias list */
        int     p_proto;        /* protocol number */
};

p_name  The official name of the protocol.  
p_aliases    A zero terminated list of alternate names for the protocol.  
p_proto  The protocol number.  

#include<netinet/in.h>
#include<arpa/inet.h>
#include<stdio.h>
#include<string.h>
#include<netdb.h>
Int main()
{
struct protoent *p =0;
char *protoname="tcp";
p=getprotobyname(protoname);
if(p!=NULL)
printf("protocol not supported:");
else
printf("protocol supported");
return 0;
}

Protocol supported/not supported based on the support for protocol

#include<netinet/in.h>
#include<arpa/inet.h>
#include<stdio.h>
#include<string.h>
#include<netdb.h>
int main()
	{
	struct protoent *p =0;
	int protonum=6;
	p=getprotobynumber(protonum);
	if(p!=NULL)
		printf("protocol not supported:");
	else
		printf("protocol supported");
	return 0;
	}

Protocol supported/not supported based on the support for protocol

 s_name The official name of the service.
 s_aliases
  A zero terminated list of alternate names for the service.
 s_port The port number at which the service resides.
 Port numbers are returned in network byte order.
 s_proto The name of the protocol to use when contacting the
 service.

The getservent, getservbyname, and getservbyport functions
each return a pointer to an object with the
following structure
containing the broken-out
fields of a line in the network services data base, c:/sys/data/services. 
structservent {
char*s_name;/* official name of service */
char**s_aliases;/* alias list */
ints_port;/* port service resides at */
char*s_proto;/* protocol to use */
};

#include<stdio.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<string.h>
#include<netdb.h>
int main()
{
Char *service="http";
Char *protocol="tcp";
Struct servent *p=0;
P=getservbyname(service,protocol);
if(p!=NULL)
printf("service not supported:");
else
printf("Service  supported");
return 0;
}

#include<stdio.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<string.h>
#include<netdb.h>
int main()
{
struct servent *p;
char *protocol="tcp";
int port;
port=htons(80);
p=(port,protocol);
if(p)
{
Printf("port is  assigned");
else
printf("port is not assigned");
}

Port is assigned

#include<stdio.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<string.h>
#include<netdb.h>
Int main()
{
struct servent *p;
p=getservent();
if(p)
printf("getservent successful");
else
printf("getservent failed");
return 0;
}

Getservent passed

#include<stdio.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<string.h>
#include<netdb.h>
int main()
{
int stayopen=1;
retservent(stayopen):
return 0;
}

#include<stdio.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<string.h>
#include<netdb.h>
int main()
{
struct servent *p;
  p=getservent();
if(p)
endservent();
return 0;
}