Get a protocol entry, given a number
#include <netdb.h> struct protoent * getprotobynumber( int proto );
The getprotobynumber() function gets the protocol entry for the given number. It returns a pointer to structure of type protoent, which contains the broken-out fields of a line in the network protocol database, /etc/protocols.
The setprotoent() function opens and rewinds the file. If you pass a nonzero stayopen argument to setprotoent(), the protocol database isn't closed after each call to getprotobyname() or getprotobynumber().
The getprotobyname() and getprotobynumber() functions sequentially search from the beginning of the file until a matching protocol name or protocol number is found, or until EOF is encountered.
A pointer to a valid protoent structure, or NULL if an error occurs.
| Safety: | |
|---|---|
| Cancellation point | Yes |
| Interrupt handler | No |
| Signal handler | No |
| Thread | No |
This function uses static data; if you need the data for future use, copy it before any subsequent calls overwrite it.
Currently, only the Internet protocols are understood.