getprotobynumber

Name

getprotobynumber, getprotobyname
- get protocol entry

Library

libc.lib

Synopsis

#include <netdb.h>

struct protoent * getprotobyname (const char *name);

struct protoent * getprotobynumber (int proto);

Return values

Null pointer (0) returned on error.

Detailed description

The getprotobyname, and getprotobynumber functions each return a pointer to an object with the following structure from the network protocol data base

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

The members of this structure are:

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.

The getprotobyname function and getprotobynumber sequentially search from the beginning of the database until a matching protocol name or protocol number is found,

Examples

#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;
}

Output

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;
}

Output

Protocol supported/not supported based on the support for protocol

The getprotobynumber, getprotobyname, functions appeared in BSD 4.2 .

Bugs

These functions use a thread-specific data space; if the data is needed for future use, it should be copied before any subsequent calls overwrite it. Only the Internet protocols are currently understood.

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