Since the routines that set h_errno can also set errno , this section explains the relationship between the two variables.

A given routine failure does not set both h_errno and errno for the same failure. A routine failure sets either h_errno or errno depending on which is appropriate for the failing condition.

For example, consider the following program:

/* Demonstrate relationship between errno and h_errno */ /* from Appendix A of the reference manual */ #include <errno.h> #include <stdio.h> #include <netdb.h> main() { static char hostname[256]; struct hostent *hostentptr; errno = 0; h_errno = 0; if ((hostentptr = gethostbyname("hndy")) == NULL) { printf("unknown host name errno is: %d h_errno is: %d\n", errno, h_errn perror("p_gethostbyname"); herror("h_gethostbyname"); } errno = 0; h_errno = 0; if ((hostentptr = gethostbyname(0)) == NULL) { printf("illegal host name errno is: %d h_errno is: %d\n", errno, h_errn perror("p_gethostbyname"); herror("h_gethostbyname"); } }

In the first call to gethostbyname , the host name parameter "hndy" does not represent a known host. In this case, gethostbyname sets h_errno to HOST_NOT_FOUND , but does not set errno .

The call to perror in this example would output:

p_gethostbyname: Error 0

The call to herror in this example would print a message describing the failure:

h_gethostbyname: Unknown

In the second call to gethostbyname , the host name parameter is 0 (zero), an invalid argument. In this case, gethostbyname sets errno to EINVAL , but does not set h_errno .

A call to perror would print a message describing the failure:

p_gethostbyname: Invalid

A call to herror would print:

h_gethostbyname: Error 0

A.7 TCP/IP Interface Enhancements

The Compaq C RTL provides the language bindings for a 4.4BSD-compatible TCP/IP implementation. The underlying 4.4BSD semantics for the specific TCP/IP routines are the responsibility of the TCP/IP back-end vendors.

With 4.4BSD semantics, gethostbyname and gethostbyaddr set the external variable h_errno . Other routines (see Table A-3) deal with 4.4BSD versions of the sockaddr and msghdr data structures. See the <socket.h> header file for a description of these structures.

The TCP/IP backend routines need to know the following:

• Whether gethostbyname and gethostbyaddr should set h_errno .
• What type of sockaddr and msghdr structures the Compaq C RTL is passing them---those defined by 4.4BSD systems, or those defined by pre-4.4BSD systems).

This information is controlled by the _SOCKADDR_LEN feature-test macro (see Section 1.5).

Compiling with _SOCKADDR_LEN defined will enable the entry points that have 4.4BSD semantics. See Table A-3. Otherwise, entry points expecting pre-4.4BSD semantics are enabled.

Table A-3 4.4BSD Entry Points

__bsd44_accept	__bsd44_gethostbyaddr	__bsd44_recvfrom
__bsd44_bind	__bsd44_gethostbyname	__bsd44_recvmsg
__bsd44_connect	__bsd44_getpeername	__bsd44_sendto
	__bsd44_getsockname	__bsd44_sendmsg

A.8 Summary of Socket Routines

This section groups and briefly describes the socket routines. For complete descriptions, see the routine reference section that follows in this appendix.

A.8.1 Basic Communication Routines

Table A-4 lists the basic communication routines that make up the building blocks of Internet programs.

Table A-4 Basic Communication Routines

Routine	Description
accept	Accepts a connection on a socket.
bind	Binds a name to a socket.
close	Closes a connection and deletes a socket descriptor.
connect	Initiates a connection on a socket.
ioctl	Controls socket operations only.
listen	Sets the maximum limit of outstanding connection requests for a socket.
read	Reads bytes from a file or socket and places them into a buffer.
readv	Not implemented.
recv	Receives bytes from a socket and places them into a buffer.
recvfrom	Receives bytes for a socket from any source.
recvmsg	Receives bytes from a socket and places them into scattered buffers.
select	Allows the polling or checking of a group of sockets.
send	Sends bytes through a socket to a connected peer.
sendmsg	Sends gathered bytes through a socket to any other socket.
sendto	Sends bytes through a socket to any other socket.
shutdown	Shuts down all or part of a bidirectional socket.
socket	Creates an endpoint for communication by returning a socket descriptor.
write	Writes bytes from a buffer to a file or socket.
writev	Not implemented.

A.8.2 Auxiliary Communication Routines

Table A-5 lists the auxiliary communication routines. These routines are used to provide information about a socket and to set the options on a socket.

Table A-5 Auxiliary Communication Routines

Routine	Description
getpeername	Returns the name of the connected peer.
getsockname	Returns the name associated with a socket.
getsockopt	Returns the options set on a socket.
setsockopt	Sets options on a socket.

A.8.3 h_errno Support Routines

Table A-6 lists the h_errno support routines. These routines map and write error-message strings generated by the external integer h_errno .

Table A-6 Supported h_errno Routines

Routine	Description
herror	Writes a message explaining a routine error.
hstrerror	Accesses message explaining routine errors.

A.8.4 Communication Support Routines

Table A-7 lists the communication support routines. These routines perform operations such as searching databases, converting byte order of network and host addresses, reading records, and returning Internet addresses.

Table A-7 Supported Communication Routines

Routine	Description
decc$get_sdc	Returns the socket device's OpenVMS I/O channel associated with a socket descriptor. vaxc$get_sdc and decc$get_sdc are synonyms for the same routine.
endhostent	Closes retrieval of network host entries and closes the network host file.
endnetent	Closes the networks database file.
endprotoent	Closes the protocols database file.
endservent	Closes the network services database file.
gethostaddr	Returns the standard host address for the processor.
gethostbyaddr	Searches the host database for a host record with a given address.
gethostbyname	Searches the host database for a host record with a given name or alias.
gethostname	Returns the name of the current host.
gethostent	Opens the network host entry by name from the network host database file.
getnetbyaddr	Searches the network database for a network record with a given address.
getnetbyname	Searches the network database for a network record with a given name or alias.
getnetent	Gets a network file entry from the networks database file.
getprotobyname	Searches the protocols database until a matching protocol name is found or until EOF is encountered.
getprotobynumber	Searches the protocols database until a matching protocol number is found or until EOF is encountered.
getprotoent	Gets a protocol database entry from the protocols database file.
getservbyname	Gets information on the named service from the network services database.
getservbyport	Gets information on the named port from the network services database.
getservent	Gets a services file entry from the network services database file.
hostalias	Searches for host aliases associated with a name.
htonl	Converts longwords from network to host byte order.
htons	Converts short integers from network to host byte order.
inet_addr	Converts Internet addresses in text form into numeric Internet addresses.
inet_lnaof	Returns the local network address portion of an Internet address.
inet_makeaddr	Returns an Internet address given a network address and a local address on that network.
inet_netof	Returns the Internet network address portion of an Internet address.
inet_network	Converts a null-terminated text string representing an Internet network address into a network address in network byte order.
inet_ntoa	Converts an Internet address into an ASCIZ (null-terminated) string.
ntohl	Converts longwords from host to network byte order.
ntohs	Converts short integers from host to network byte order.
sethostent	Opens, rewinds, and closes the network host database file.
setnetent	Opens, rewinds, and closes the networks database file.
setprotoent	Opens, rewinds, and closes the protocols database file.
setservent	Opens, rewinds, and closes the network services database file.
decc$socket_fd	Returns the socket descriptor associated with a Socket Device Channel for direct use with the Compaq C RTL.
vaxc$get_sdc	Returns the socket device's OpenVMS I/O channel associated with a socket descriptor. vaxc$get_sdc and decc$get_sdc are synonyms for the same routine.

Accepts a connection on a socket.

Format

#include <socket.h>

int accept (int s, struct sockaddr *addr, int *addrlen);

(_DECC_V4_SOURCE) int accept (int s, struct sockaddr *addr, size_t *addrlen);

(NOT _DECC_V4_SOURCE)

Arguments

s

A socket descriptor that has been returned by socket , subsequently bound to an address with bind , and that is listening for connections after a listen .

addr

A result parameter that is filled in with the address of the connecting entity, as known to the communications layer. The exact format of the structure to which the address parameter points is determined by the domain in which the communication is occurring. This version of Compaq C supports only the Internet domain (AF_INET).

addrlen

A value-result parameter; it should initially contain the size of the structure pointed to by addr. On return it will contain the actual length, in bytes, of the structure that has been filled in by the communication layer. See <socket.h> for a description of the sockaddr structure.

Description

This routine completes the first connection on the queue of pending connections, creates a new socket with the same properties as s, and allocates and returns a new descriptor for the socket. If no pending connections are present on the queue, and the socket is not marked as nonblocking, accept blocks the caller until a connection request is present. If the socket is marked nonblocking by using a setsockopt call and no pending connections are present on the queue, accept returns an error. The accepted socket may not be used to accept connections. The original socket s remains open (listening) for other connection requests. This call is used with connection-based socket types, currently with SOCK_STREAM.

It is possible to select a socket for the purposes of performing an accept by selecting it for read.

See also bind , connect , listen , select , and socket in this section.

Return Values

x

A nonnegative integer that is a descriptor for the accepted socket.

--1

Indicates an error; errno is set to one of the following: EBADF -- The socket descriptor is invalid. ENOTSOCK -- The socket descriptor references a file, not a socket. EOPNOTSUPP -- The reference socket is not of type SOCK_STREAM. EFAULT -- The addr parameter is not in a writable part of the user address space. EWOULDBLOCK -- The socket is marked nonblocking and no connections are present to be accepted.

Binds a name to a socket.

Format

#include <socket.h>

int bind (int s, struct sockaddr *name, int namelen);

(_DECC_V4_SOURCE) int bind (int s, const struct sockaddr *name, size_t namelen);

(NOT _DECC_V4_SOURCE)

Arguments

s

A socket descriptor that has been created with socket .

name

Address of a structure used to assign a name to the socket in the format specific to the family (AF_INET) socket address. See <socket.h> for a description of the sockaddr structure.

namelen

The size, in bytes, of the structure pointed to by name.

Description

This routine assigns a name to an unnamed socket. When a socket is created with socket it exists in a name space (address family) but has no name assigned. The bind routine requests that a name be assigned to the socket.

See also connect , getsockname , listen , and socket in this appendix.

Return Values

0

Indicates success.

--1

Indicates an error; errno is set to one of the following values: EBADF -- The socket descriptor is invalid. ENOTSOCK -- The socket descriptor references a file, not a socket. EADDRNOTAVAIL -- specified address is not available from the local machine. EADDRINUSE -- The specified Internet address and ports are already in use. EINVAL -- The socket is already bound to an address. EACCESS -- The requested address is protected, and the current user has inadequate permission to access it. EFAULT -- The name parameter is not a valid part of the user address space.