# NET - [Overview](#section1787027955165622) - [Summary](#section1322897020165622) - [Files](#files) - [Data Structures](#nested-classes) - [Macros](#define-members) - [Typedefs](#typedef-members) - [Functions](#func-members) - [Details](#section2074466484165622) - [Function](#section1845007127165622) - [accept\(\)](#ga0807af5ac9dfc2a63624e8c3e0ae95ef) - [bind\(\)](#ga82199bcd81894331533a25f08e172480) - [connect\(\)](#gacdfd99b6c59c833776412fbb0c539efb) - [dn\_comp\(\)](#ga0438570faf515401bffa1a0d9c94a266) - [dn\_expand\(\)](#ga91eb2055a64b28e4942a3a760d747243) - [ether\_aton\(\)](#gaab4c5b65c36fc0ea96a017daabc3770a) - [ether\_aton\_r\(\)](#gac0954821754bace30f674e61bb9f4e5f) - [ether\_ntoa\(\)](#ga07e34e6ee9e272c4799780915d11677c) - [ether\_ntoa\_r\(\)](#ga245e21de8e82756712a5182c2674c2ad) - [freeifaddrs\(\)](#gabfdd6ca5469fe73ed88ba94bf8db57cc) - [getpeername\(\)](#ga13d77555ad4ed62dfef0ce32dd16755c) - [getprotobyname\(\)](#ga83ac8a97dd9d895cda658af3aa46fd55) - [getprotobynumber\(\)](#gac01697dc4a5b8e434522220913bd46ea) - [getprotoent\(\)](#gaca0da70657afbc3e723990bb229deec3) - [getsockname\(\)](#ga62577da7dba23abb9c99cf5c2800ab24) - [getsockopt\(\)](#gacfcf672e255123afb75ed4d326257073) - [herror\(\)](#gaa68de2578d4e0849f82d70b2f5b9af70) - [hstrerror\(\)](#gac1752c48d9cf2ff87e29f29df6caa585) - [htonl\(\)](#gac7eed08cd3b67f42bf56063157c8fd55) - [htons\(\)](#gaabce0f8d453c3380e5b8a3d4947eb48c) - [if\_freenameindex\(\)](#ga7fe55c04ac2116fa501338fdcb279cc9) - [inet\_addr\(\)](#ga617651ec952a1f4c9cbddbf78f4b2e2e) - [inet\_aton\(\)](#ga26ee8e8e3949699a9c0e02ece272d370) - [inet\_lnaof\(\)](#ga1facb1380b7657ca9c72fb2633b60e3b) - [inet\_makeaddr\(\)](#gab28732d1d740597f53fb65a09d97800c) - [inet\_netof\(\)](#ga3a96aa4e6abe8e6959ea63fe338174dd) - [inet\_network\(\)](#ga6f478437c4810fce89cf0e77d94181f8) - [inet\_ntoa\(\)](#ga08b9fff487151e004d9862cbf34a51ad) - [inet\_ntop\(\)](#gae9a2182ca3255f16723adeea14665b55) - [inet\_pton\(\)](#ga3f6e2b2dae98a409d77c6e3b0cebc04b) - [listen\(\)](#ga5989c21d05cb17caba26cef496a7beea) - [ntohl\(\)](#gae68530d41f32dfef707f20b2bbaa5a44) - [ntohs\(\)](#gaf8c87af507c59bd8fef112e5e35fe537) - [recv\(\)](#ga5d049263cd0e3206b93530e68dfd7403) - [recvfrom\(\)](#ga3089d3ee59e26bd4def3ef870175540e) - [recvmsg\(\)](#gaaba92f19a31c01b93e3391671a8b3dd5) - [send\(\)](#ga4053f5c8e26fd490ef54e2a0abf5c89f) - [sendmsg\(\)](#ga70c97d3a1eab72cba4461d66a1778570) - [sendto\(\)](#ga2587b27d2c6014c6b568a974655f41c5) - [setprotoent\(\)](#ga6a806414e4ae5bffb09e3a1d25d8db75) - [setsockopt\(\)](#ga81983de50d79d797b2ac0f0d0f28953f) - [shutdown\(\)](#ga402425b8e1ceab40ac38a949babcf1aa) - [socket\(\)](#gaf4e0711877c45a41168ac677b0670ccd) ## **Overview** **Description:** Provides functions and data structures related to network operations. **Since:** 1.0 **Version:** 1.0 ## **Summary** ## Files

File Name	Description
inet.h	Provides functions and data structures related to network operations.
ifaddrs.h	Provides functions and data structures related to network operations.
if.h	Provides functions and data structures related to network operations. For example, you can use the functions to send and receive network data, manage network addresses, and convert bytes.
netdb.h	Provides functions and data structures related to network operations. For example, you can use the functions to send and receive network data, manage network addresses, and convert bytes.
ether.h	Provides functions and data structures related to network operations. For example, you can use the functions to send and receive network data, manage network addresses, and convert bytes.
ethernet.h	Declares the structures related to an Ethernet address.
in.h	Declares the data structures and macros related to network operations.
resolv.h	Provides functions and data structures related to network operations. For example, you can use the functions to send and receive network data, manage network addresses, and convert bytes.
socket.h	Declares functions and data structures related to network sockets.

## Data Structures

Data Structure Name	Description
ifaddrs	Defines the network interface information.
if_nameindex	Defines the network adapter information.
hostent	Describes the host name and address information.
protoent	Describes the protocol database information.
ether_addr	Defines the information about a 48-bit Ethernet address.
in_addr	Describes the network address information.
sockaddr	Describes the socket address information.

## Macros

Macro Name and Value	Description
h_addr h_addr_list[0]	Defines the first address in h_addr_list for compatibility.
ETH_ALEN 6	Defines the length of an Ethernet address.
SHUT_RD 0	Disables reading data from a socket.
SHUT_WR 1	Disables writing data to a socket.
SHUT_RDWR 2	Disables reading data from and writing data to a socket.
PF_INET 2	Defines the IPv4 internet protocol family.
PF_INET6 10	Defines the IPv6 internet protocol family.
AF_INET PF_INET	Defines the IPv4 internet address.
AF_INET6 PF_INET6	Defines the IPv6 internet address.
SOCK_STREAM 1	Defines stream sockets.
SOCK_DGRAM 2	Defines datagram sockets.
SOCK_RAW 3	Defines raw sockets.
MSG_DONTWAIT 0x0040	Defines the message type of a non-blocking operation.
MSG_NOSIGNAL 0x4000	Defines the message type that does not generate a signal.
MSG_MORE 0x8000	Defines the message type that more data is to be transferred.
SO_TYPE 3	Obtains the socket type.
SO_DONTROUTE 5	Prohibits messages from being sent via a gateway.
SO_BROADCAST 6	Enables sending broadcast messages.
SO_SNDBUF 7	Defines the size of the socket sending buffer, in bytes.
SO_RCVBUF 8	Defines the size of the socket receiving buffer, in bytes.
SO_RCVTIMEO 66	Defines the data receiving timeout interval.
SO_SNDTIMEO 67	Defines the data sending timeout interval.
SO_BINDTODEVICE 25	Binds the socket to a particular device.
SOL_SOCKET 1	Defines the layers of a socket.

## Typedefs

Typedef Name	Description
in_addr_t	typedef uint32_t Defines the data type of a network address.

Typedef Name

Description

in_addr_t

typedef uint32_t

Defines the data type of a network address.

## Functions

Function	Description
htonl (uint32_t n)	uint32_t Converts an integer from the host byte order to the network byte order.
htons (uint16_t n)	uint16_t Converts a 16-bit integer from the host byte order to the network byte order.
ntohl (uint32_t n)	uint32_t Converts an integer from the network byte order to the host byte order.
ntohs (uint16_t n)	uint16_t Converts a 16-bit integer from the network byte order to the host byte order.
inet_addr (const char *p)	in_addr_t Converts a string from the IPv4 numbers-and-dots notation to the binary data in network byte order.
inet_network (const char *p)	in_addr_t Converts a string from the IPv4 numbers-and-dots notation to the binary data in host byte order.
inet_ntoa (struct in_addr in)	char * Converts a network address to a string in dotted-decimal format.
inet_pton (int af, const char __restrict s, void __restrict a0)	int Converts a string to a network address in the specified address family.
inet_ntop (int af, const void restrict a0, char restrict s, socklen_t l)	const char * Converts a network address in the specified address family to a string.
inet_aton (const char s0, struct in_addr dest)	int Converts an IP address from the string format to the 32-bit binary format in network byte order.
inet_makeaddr (in_addr_t n, in_addr_t h)	struct in_addr Converts the network number and host address to the network address.
inet_lnaof (struct in_addr in)	in_addr_t Converts an IP address into a host ID in host byte order without network bits.
inet_netof (struct in_addr in)	in_addr_t Extracts the network number from the in_addr structure and converts it to the host byte order.
freeifaddrs (struct ifaddrs *ifp)	void Frees the network interface information obtained by getifaddrs.
if_freenameindex (struct if_nameindex *idx)	void Frees the network adapter information obtained by if_nameindex.
setprotoent (int stayopen)	void Opens a connection to the database and sets the next entry to the first entry.
getprotoent (void)	struct protoent * Retrieves the current protocol information.
getprotobyname (const char *name)	struct protoent * Retrieves the information about a specified protocol.
getprotobynumber (int num)	struct protoent * Retrieves the information about a protocol with the specified number.
herror (const char *msg)	void Prints error information.
hstrerror (int ecode)	const char * Retrieves error information associated with the specified error number.
ether_ntoa (const struct ether_addr *p_a)	char * Converts binary data in network byte order into a standard 48-bit Ethernet host address in the colon hexadecimal notation.
ether_aton (const char *x)	struct ether_addr * Converts a standard 48-bit Ethernet host address in the colon hexadecimal notation into binary data in network byte order.
ether_ntoa_r (const struct ether_addr p_a, char x)	char * Converts binary data in network byte order into a standard 48-bit Ethernet host address in the colon hexadecimal notation. This function is reentrant.
ether_aton_r (const char x, struct ether_addr p_a)	struct ether_addr * Converts a standard 48-bit Ethernet host address in the colon hexadecimal notation into binary data in network byte order. This function is reentrant.
dn_comp (const char src, unsigned char dst, int space, unsigned char dnptrs, unsigned char lastdnptr)	int Compresses a network domain name.
dn_expand (const unsigned char base, const unsigned char end, const unsigned char src, char dest, int space)	int Expands a compressed domain name to a full domain name.
socket (int domain, int type, int protocol)	int Creates a socket and returns its descriptor.
shutdown (int sockfd, int how)	int Shuts down a socket.
bind (int sockfd, const struct sockaddr *addr, socklen_t addrlen)	int Binds a local protocol address to a socket.
connect (int sockfd, const struct sockaddr *addr, socklen_t addrlen)	int Connects a socket to the specified address.
listen (int sockfd, int backlog)	int Listens for network connection requests on a socket.
accept (int sockfd, struct sockaddr __restrict addr, socklen_t __restrict addrlen)	int Accepts a connection request on a socket.
getsockname (int fd, struct sockaddr restrict addr, socklen_t restrict len)	int Retrieves the local address of the specified socket.
getpeername (int fd, struct sockaddr restrict addr, socklen_t restrict len)	int Retrieves the peer address of the specified socket.
send (int fd, const void *buf, size_t len, int flags)	ssize_t Sends data to another socket.
recv (int fd, void *buf, size_t len, int flags)	ssize_t Receives data from another socket.
sendto (int fd, const void buf, size_t len, int flags, const struct sockaddr addr, socklen_t alen)	ssize_t Sends data to another socket.
recvfrom (int fd, void __restrict buf, size_t len, int flags, struct sockaddr __restrict addr, socklen_t *__restrict alen)	ssize_t Receives data from a specified socket.
sendmsg (int fd, const struct msghdr *msg, int flags)	ssize_t Sends data to another socket.
recvmsg (int fd, struct msghdr *msg, int flags)	ssize_t Receives data from a specified socket.
getsockopt (int fd, int level, int optname, void __restrict optval, socklen_t __restrict optlen)	int Retrieves the socket options.
setsockopt (int fd, int level, int optname, const void *optval, socklen_t optlen)	int Sets the socket options.

## **Details** ## **Function ** ## accept\(\) ``` int accept (int sockfd, struct [sockaddr](sockaddr.md) *__restrict addr, [socklen_t](UTILS.md#ga531675af4e35aaa1cc9aeefa6cc2ccc4) *__restrict addrlen ) ``` **Description:** Accepts a connection request on a socket. This function is used for waiting for a connection request from the client and for TCP only. **Parameters:**

Name	Description
sockfd	Indicates the socket descriptor.
addr	Indicates the pointer to the socket address requiring for the connection.
addrlen	Indicates the length of the address structure pointed to by addr.

**Returns:** Returns a valid socket if the operation is successful; returns **-1** and sets **errno** to a value in the following table if the operation fails.

errno	Description
EINVAL	Invalid input parameter
EOPNOTSUPP	The socket requiring for the connection is not of the NETCONN_TCP type.
EWOULDBLOCK	Failure to receive events in non-blocking mode.
ENFILE	Failure to creat a new socket.
ECONNABORTED	Failure to receive the remote information.
ENOMEM	Memory copy exception.

## bind\(\) ``` int bind (int sockfd, const struct [sockaddr](sockaddr.md) * addr, [socklen_t](UTILS.md#ga531675af4e35aaa1cc9aeefa6cc2ccc4) addrlen ) ``` **Description:** Binds a local protocol address to a socket. This function is called by the server. **Parameters:**

Name	Description
sockfd	Indicates the socket descriptor.
addr	Indicates the address to be bound to the socket.
addrlen	Indicates the length of the address structure pointed to by addr.

**Returns:** Returns **0** if the operation is successful; returns **-1** and sets **errno** to a value in the following table if the operation fails.

errno	Description
EINVAL	Invalid input parameter

## connect\(\) ``` int connect (int sockfd, const struct [sockaddr](sockaddr.md) * addr, [socklen_t](UTILS.md#ga531675af4e35aaa1cc9aeefa6cc2ccc4) addrlen ) ``` **Description:** Connects a socket to the specified address. This function is for a connection request from the client and for TCP only. **Parameters:**

Name	Description
sockfd	Indicates the socket descriptor.
addr	Indicates the pointer to the address to be connected.
addrlen	Indicates the length of the address structure pointed to by addr.

**Returns:** Returns **0** if the operation is successful; returns **-1** and sets **errno** to a value in the following table if the operation fails.

errno	Description
EINVAL	Invalid input parameter
EBADF	Invalid socket or socket status exception
EIO	Incorrect connection type obtained based on the socket descriptor
ECONNREFUSED	Restart due to connection failure
ECONNABORTED	Shut-down due to connection failure

## dn\_comp\(\) ``` int dn_comp (const char * src, unsigned char * dst, int space, unsigned char ** dnptrs, unsigned char ** lastdnptr ) ``` **Description:** Compresses a network domain name. To reduce the size of DNS messages, domain names in the messages are compressed. For details about the compression scheme, see RFC 1035. **Parameters:**

Name	Description
src	Indicates the pointer to the domain name to be compressed.
dst	Indicates the pointer to the compressed domain name.
space	Indicates the size of the compressed domain name.
dnptrs	Indicates the pointer to an array of pointers to previously compressed domain names. If the value is NULL, the current domain name will not be compressed.
lastdnptr	Indicates the pointer to the last element of the array. If the value is NULL, the array is not updated.

**Returns:** Returns the length of the compressed domain name if the operation is successful; returns **-1** otherwise. ## dn\_expand\(\) ``` int dn_expand (const unsigned char * base, const unsigned char * end, const unsigned char * src, char * dest, int space ) ``` **Description:** Expands a compressed domain name to a full domain name. The compressed domain name is contained in a query or reply message. **Parameters:**

Name	Description
base	Indicates the pointer to the start of the DNS message body.
end	Indicates the pointer to the end of the DNS message body.
src	Indicates the pointer to the compressed domain name.
dest	Indicates the pointer to the expanded domain name.
space	Indicates the memory size of the dest address.

**Returns:** Returns the length of the compressed domain name if the operation is successful; returns **-1** otherwise. ## ether\_aton\(\) ``` struct [ether_addr](ether_addr.md)* ether_aton (const char * x) ``` **Description:** Converts a standard 48-bit Ethernet host address in the colon hexadecimal notation into binary data in network byte order. **Parameters:**

Name	Description
x	Indicates the pointer to the host address to be converted.

**Returns:** Returns the binary data if the operation is successful; returns **0** otherwise. ## ether\_aton\_r\(\) ``` struct [ether_addr](ether_addr.md)* ether_aton_r (const char * x, struct [ether_addr](ether_addr.md) * p_a ) ``` **Description:** Converts a standard 48-bit Ethernet host address in the colon hexadecimal notation into binary data in network byte order. This function is reentrant. This function is used in multitasking scenarios. **Parameters:**

Name	Description
x	Indicates the pointer to the host address to be converted.
p_a	Indicates the pointer to the temporary buffer during conversion.

**Returns:** Returns the binary data represented by **[ether\_addr](ether_addr.md)** if the operation is successful; returns **0** otherwise. ## ether\_ntoa\(\) ``` char* ether_ntoa (const struct [ether_addr](ether_addr.md) * p_a) ``` **Description:** Converts binary data in network byte order into a standard 48-bit Ethernet host address in the colon hexadecimal notation. **Parameters:**

Name	Description
p_a	Indicates the pointer to the binary data to be converted.

**Attention:** Different from glibc \(for example, 1:2:3:4:5:f\), 0 is prefixed and letters are capitalized \(for example, 01:02:03:04:05:0F\). **Returns:** Returns the host address if the operation is successful; returns **0** otherwise. ## ether\_ntoa\_r\(\) ``` char* ether_ntoa_r (const struct [ether_addr](ether_addr.md) * p_a, char * x ) ``` **Description:** Converts binary data in network byte order into a standard 48-bit Ethernet host address in the colon hexadecimal notation. This function is reentrant. This function is used in multitasking scenarios. **Parameters:**

Name	Description
p_a	Indicates the pointer to the binary data to be converted.
x	Indicates the pointer to the temporary buffer during conversion.

**Attention:** Different from glibc \(for example, 1:2:3:4:5:f\), 0 is prefixed and letters are capitalized \(for example, 01:02:03:04:05:0F\). **Returns:** Returns the host address if the operation is successful; returns **0** otherwise. ## freeifaddrs\(\) ``` void freeifaddrs (struct [ifaddrs](ifaddrs.md) * ifp) ``` **Description:** Frees the network interface information obtained by **getifaddrs**. **Parameters:**

Name	Description
ifp	Indicates the pointer to the network interface information to be freed.

## getpeername\(\) ``` int getpeername (int fd, struct [sockaddr](sockaddr.md) *restrict addr, [socklen_t](UTILS.md#ga531675af4e35aaa1cc9aeefa6cc2ccc4) *restrict len ) ``` **Description:** Retrieves the peer address of the specified socket. **Parameters:**

Name	Description
fd	Indicates the socket descriptor.
addr	Indicates the pointer to the address to be retrieved.
len	Indicates the pointer to the length of the address pointed to by addr.

**Returns:** Returns **0** if the operation is successful; returns **-1** and sets **errno** to a value in the following table if the operation fails.

errno	Description
EINVAL	Invalid input parameter
EBADF	Invalid socket or socket status exception
ENOMEM	Memory copy exception

## getprotobyname\(\) ``` struct [protoent](protoent.md)* getprotobyname (const char * name) ``` **Description:** Retrieves the information about a specified protocol. **Parameters:**

Name	Description
name	Indicates the pointer to the protocol name.

Name	Description
num	Indicates the protocol number.

**Attention:** The **/etc/protocols** configuration file is not supported. Only the following built-in protocols are supported: ip/icmp/igmp/ggp/ipencap/st/tcp/egp/pup/udp/hmp/xns-idp/rdp/iso-tp4/xtp/ ddp/idpr-cmtp/ipv6/ipv6-route/ipv6-frag/idrp/rsvp/gre/esp/ah/skip/ipv6-icmp/ ipv6-nonxt/ipv6-opts/rspf/vmtp/ospf/ipip/encap/pim/raw \(This protocol does not have the **aliases** attribute, that is, **aliases** is empty.\) **Returns:** Returns the pointer to the protocol information if the operation is successful; returns **NULL** otherwise. ## getprotoent\(\) ``` struct [protoent](protoent.md)* getprotoent (void ) ``` **Description:** Retrieves the current protocol information. **Attention:** The **/etc/protocols** configuration file is not supported. Only the following built-in protocols are supported: ip/icmp/igmp/ggp/ipencap/st/tcp/egp/pup/udp/hmp/xns-idp/rdp/iso-tp4/xtp/ ddp/idpr-cmtp/ipv6/ipv6-route/ipv6-frag/idrp/rsvp/gre/esp/ah/skip/ipv6-icmp/ ipv6-nonxt/ipv6-opts/rspf/vmtp/ospf/ipip/encap/pim/raw \(This protocol does not have the **aliases** attribute, that is, **aliases** is empty.\) **Returns:** Returns the pointer to the protocol information if the operation is successful; returns **NULL** otherwise. ## getsockname\(\) ``` int getsockname (int fd, struct [sockaddr](sockaddr.md) *restrict addr, [socklen_t](UTILS.md#ga531675af4e35aaa1cc9aeefa6cc2ccc4) *restrict len ) ``` **Description:** Retrieves the local address of the specified socket. **Parameters:**

Name	Description
fd	Indicates the socket descriptor.
addr	Indicates the pointer to the address to be retrieved.
len	Indicates the pointer to the length of the address pointed to by addr.

**Returns:** Returns **0** if the operation is successful; returns **-1** and sets **errno** to a value in the following table if the operation fails.

errno	Description
EINVAL	Invalid input parameter
EBADF	Invalid socket or socket status exception
ENOMEM	Memory copy exception

## getsockopt\(\) ``` int getsockopt (int fd, int level, int optname, void *__restrict optval, [socklen_t](UTILS.md#ga531675af4e35aaa1cc9aeefa6cc2ccc4) *__restrict optlen ) ``` **Description:** Retrieves the socket options. **Parameters:**

Name	Description
fd	Indicates the socket descriptor.
level	Indicates the protocol level at which the option resides. Only SOL_SOCKET is supported.
optname	Indicates the socket options to be retrieved, which has the following values: SO_BROADCAST: permits sending and receiving broadcast messages. SO_RCVTIMEO: defines the data receiving timeout interval. SO_RCVBUF: defines the size of the socket receiving buffer, in bytes. SO_TYPE: defines the socket type. SO_DONTROUTE: prohibits messages from being sent via a gateway. SO_BINDTODEVICE: binds this socket to a particular device.
optval	Indicates the pointer to the option data.
optlen	Indicates the pointer to the size of the buffer pointed to by optval.

**Returns:** Returns **0** if the operation is successful; returns **-1** and sets **errno** to a value in the following table if the operation fails.

errno	Description
EINVAL	Small optlen
EBADF	Invalid socket or socket status exception
EFAULT	The input parameter is a null pointer.
ENOBUFS	Retrieved length exception
ENOMEM	Memory copy exception

## herror\(\) ``` void herror (const char * msg) ``` **Description:** Prints error information. **Parameters:**

Name	Description
msg	Indicates the pointer to the string to be printed together with the error information. This parameter can be null.

**Returns:** Returns **0** if the operation is successful; returns **-1** and sets **errno** to a value in the following table if the operation fails.

errno	Description
EINVAL	Incorrect symbols or parameters
EOVERFLOW	Long item for printing

## hstrerror\(\) ``` const char* hstrerror (int ecode) ``` **Description:** Retrieves error information associated with the specified error number. **Parameters:**

Name	Description
ecode	Indicates the error number.

**Returns:** Returns the string representing the error information. ## htonl\(\) ``` uint32_t htonl (uint32_t n) ``` **Description:** Converts an integer from the host byte order to the network byte order. **Parameters:**

Name	Description
n	Indicates the integer in host byte order.

**Returns:** Returns the original data if the system is in big-endian mode; returns the converted data otherwise. ## htons\(\) ``` uint16_t htons (uint16_t n) ``` **Description:** Converts a 16-bit integer from the host byte order to the network byte order. **Parameters:**

Name	Description
n	Indicates the integer in host byte order.

**Returns:** Returns the original data if the system is in big-endian mode; returns the converted data otherwise. ## if\_freenameindex\(\) ``` void if_freenameindex (struct [if_nameindex](if_nameindex.md) * idx) ``` **Description:** Frees the network adapter information obtained by [if\_nameindex](if_nameindex.md). **Parameters:**

Name	Description
idx	Indicates the pointer to the network adapter to be freed.

## inet\_addr\(\) ``` [in_addr_t](NET.md#ga98b38134a62f24554da0ffcabde8062c) inet_addr (const char * p) ``` **Description:** Converts a string from the IPv4 numbers-and-dots notation to the binary data in network byte order. **Parameters:**

Name	Description
p	Indicates the pointer to the string to be converted.

**Returns:** Returns the converted data if the operation is successful; returns **-1** otherwise. ## inet\_aton\(\) ``` int inet_aton (const char * s0, struct [in_addr](in_addr.md) * dest ) ``` **Description:** Converts an IP address from the string format to the 32-bit binary format in network byte order. **Parameters:**

Name	Description
s0	Indicates the pointer to the IP address to be converted.
dest	Indicates the pointer to the structure for conversion.

**Returns:** Returns **1** if the operation is successful; returns **0** otherwise. ## inet\_lnaof\(\) ``` [in_addr_t](NET.md#ga98b38134a62f24554da0ffcabde8062c) inet_lnaof (struct [in_addr](in_addr.md) in) ``` **Description:** Converts an IP address into a host ID in host byte order without network bits. **Parameters:**

Name	Description
in	Indicates the network address structure.

**Returns:** Returns the converted host address. ## inet\_makeaddr\(\) ``` struct [in_addr](in_addr.md) inet_makeaddr ([in_addr_t](NET.md#ga98b38134a62f24554da0ffcabde8062c) n, [in_addr_t](NET.md#ga98b38134a62f24554da0ffcabde8062c) h ) ``` **Description:** Converts the network number and host address to the network address. **Parameters:**

Name	Description
n	Indicates the network number.
h	Indicates the host address.

**Returns:** Returns the converted network address. ## inet\_netof\(\) ``` [in_addr_t](NET.md#ga98b38134a62f24554da0ffcabde8062c) inet_netof (struct [in_addr](in_addr.md) in) ``` **Description:** Extracts the network number from the **[in\_addr](in_addr.md)** structure and converts it to the host byte order. **Parameters:**

Name	Description
in	Indicates the network address structure.

**Returns:** Returns the converted network number. ## inet\_network\(\) ``` [in_addr_t](NET.md#ga98b38134a62f24554da0ffcabde8062c) inet_network (const char * p) ``` **Description:** Converts a string from the IPv4 numbers-and-dots notation to the binary data in host byte order. **Parameters:**

Name	Description
p	Indicates the pointer to the string to be converted.

**Returns:** Returns the converted data if the operation is successful; returns **-1** otherwise. ## inet\_ntoa\(\) ``` char* inet_ntoa (struct [in_addr](in_addr.md) in) ``` **Description:** Converts a network address to a string in dotted-decimal format. **Parameters:**

Name	Description
in	Indicates the network address to be converted.

**Returns:** Returns the string. ## inet\_ntop\(\) ``` const char* inet_ntop (int af, const void *restrict a0, char *restrict s, [socklen_t](UTILS.md#ga531675af4e35aaa1cc9aeefa6cc2ccc4) l ) ``` **Description:** Converts a network address in the specified address family to a string. **Parameters:**

Name	Description
af	Indicates the address family. Currently, only AF_INET and AF_INET6 are supported.
a0	Indicates the pointer to the data to be converted.
s	Indicates the pointer to the string to be converted.
l	Indicates the size of the string to be converted.

**Returns:** Returns the converted string if the operation is successful; returns **NULL** and sets **errno** to a value in the following table if the operation fails.

errno	Description
ENOSPC	Insufficient space for conversion
EAFNOSUPPORT	Unsupported address family

## inet\_pton\(\) ``` int inet_pton (int af, const char *__restrict s, void *__restrict a0 ) ``` **Description:** Converts a string to a network address in the specified address family. **Parameters:**

Name	Description
af	Indicates the address family. Currently, only AF_INET and AF_INET6 are supported.
s	Indicates the pointer to the string to be converted.
a0	Indicates the pointer to the converted data.

**Returns:** Returns **1** if the operation is successful; returns **0** if the input address family is invalid; returns **-1** if the operation fails. The error codes are set as follows:

errno	Description
EAFNOSUPPORT	Unsupported address family

## listen\(\) ``` int listen (int sockfd, int backlog ) ``` **Description:** Listens for network connection requests on a socket. This function is for TCP only. **Parameters:**

Name	Description
sockfd	Indicates the socket descriptor.
backlog	Indicates the maximum length of the queue to accept incoming connection requests.

**Returns:** Returns **0** if the operation is successful; returns **-1** and sets **errno** to a value in the following table if the operation fails.

errno	Description
EINVAL	Invalid input parameter
EBADF	Invalid socket or socket status exception
EIO	Incorrect connection type obtained based on the socket descriptor

## ntohl\(\) ``` uint32_t ntohl (uint32_t n) ``` **Description:** Converts an integer from the network byte order to the host byte order. **Parameters:**

Name	Description
n	Indicates the integer in network byte order.

**Returns:** Returns the original data if the system is in big-endian mode; returns the converted data otherwise. ## ntohs\(\) ``` uint16_t ntohs (uint16_t n) ``` **Description:** Converts a 16-bit integer from the network byte order to the host byte order. **Parameters:**

Name	Description
n	Indicates the integer in network byte order.

**Returns:** Returns the original data if the system is in big-endian mode; returns the converted data otherwise. ## recv\(\) ``` ssize_t recv (int fd, void * buf, size_t len, int flags ) ``` **Description:** Receives data from another socket. **Parameters:**

Name	Description
fd	Indicates the socket descriptor.
buf	Indicates the pointer to a buffer for storing the data to be received.
len	Indicates the length of the buffer pointed to by buf.
flags	Indicates the socket flags. This parameter has the following values: MSG_DONTWAIT: enables the non-blocking operation. MSG_MORE: indicates that more messages are to be sent. MSG_NOSIGNAL: indicates that no signals are generated.

**Returns:** Returns the length of the received data if the operation is successful; returns **-1** and sets **errno** to a value in the following table if the operation fails.

errno	Description
EINVAL	Invalid input parameter
EBADF	Invalid socket or socket status exception
ENOMEM	Memory copy exception
EOPNOTSUPP	Unsupported message type
ENOTCONN	Socket not connected
EWOULDBLOCK	Blocking operation
ENOTCONN	Connection closed

## recvfrom\(\) ``` ssize_t recvfrom (int fd, void *__restrict buf, size_t len, int flags, struct [sockaddr](sockaddr.md) *__restrict addr, [socklen_t](UTILS.md#ga531675af4e35aaa1cc9aeefa6cc2ccc4) *__restrict alen ) ``` **Description:** Receives data from a specified socket. **Parameters:**

Name	Description
fd	Indicates the socket descriptor.
buf	Indicates the pointer to a buffer for storing the data to be received.
len	Indicates the length of the buffer pointed to by buf.
flags	Indicates the socket flags. This parameter has the following values: MSG_DONTWAIT: enables the non-blocking operation. MSG_MORE: indicates that more messages are to be sent. MSG_NOSIGNAL: indicates that no signals are generated.
addr	Indicates the pointer to the source address.
alen	Indicates the size of the source address.

**Returns:** Returns the length of the received data if the operation is successful; returns **-1** and sets **errno** to a value in the following table if the operation fails.

errno	Description
EINVAL	Invalid input parameter
EBADF	Invalid socket or socket status exception
ENOMEM	Memory copy exception
EOPNOTSUPP	Unsupported message type
ENOTCONN	Socket not connected
ENOTCONN	Connection closed

## recvmsg\(\) ``` ssize_t recvmsg (int fd, struct msghdr * msg, int flags ) ``` **Description:** Receives data from a specified socket. **Parameters:**

Name	Description
fd	Indicates the socket descriptor.
msg	Indicates the pointer to the address to receive the message header.
flags	Indicates the socket flags. This parameter has the following values: MSG_DONTWAIT: enables the non-blocking operation. MSG_MORE: indicates that more messages are to be sent. MSG_NOSIGNAL: indicates that no signals are generated.

**Attention:** This function does not allow sending ancillary data. Currently, the length of the array defined by **msg\_iov** can only be **1**. **Returns:** Returns the length of the received data if the operation is successful; returns **-1** and sets **errno** to a value in the following table if the operation fails.

errno	Description
EINVAL	Invalid input parameter
EBADF	Invalid socket or socket status exception
EDESTADDRREQ	Invalid connection
ENOMEM	Memory copy exception
EIO	Incorrect connection type obtained based on the socket descriptor

## send\(\) ``` ssize_t send (int fd, const void * buf, size_t len, int flags ) ``` **Description:** Sends data to another socket. **Parameters:**

Name	Description
fd	Indicates the socket descriptor.
buf	Indicates the pointer to a buffer for storing the data to be sent.
len	Indicates the length of the buffer pointed to by buf.
flags	Indicates the socket flags. This parameter has the following values: MSG_DONTWAIT: enables the non-blocking operation. MSG_MORE: indicates that more messages are to be sent. MSG_NOSIGNAL: indicates that no signals are generated.

**Returns:** Returns the length of the sent data if the operation is successful; returns **-1** and sets **errno** to a value in the following table if the operation fails.

errno	Description
EINVAL	Invalid input parameter
EBADF	Invalid socket or socket status exception
EDESTADDRREQ	Invalid connection
ENOMEM	Memory copy exception
EOPNOTSUPP	Unsupported message type
ENOTCONN	Socket not connected
EIO	Incorrect connection type obtained based on the socket descriptor

## sendmsg\(\) ``` ssize_t sendmsg (int fd, const struct msghdr * msg, int flags ) ``` **Description:** Sends data to another socket. **Parameters:**

Name	Description
fd	Indicates the socket descriptor.
msg	Indicates the pointer to the address of the message header to be sent.
flags	Indicates the socket flags. This parameter has the following values: MSG_DONTWAIT: enables the non-blocking operation. MSG_MORE: indicates that more messages are to be sent. MSG_NOSIGNAL: indicates that no signals are generated.

**Attention:** This function does not support ancillary data. **Returns:** Returns the length of the sent data if the operation is successful; returns **-1** and sets **errno** to a value in the following table if the operation fails.

errno	Description
EINVAL	Invalid input parameter
EBADF	Invalid socket or socket status exception
EDESTADDRREQ	Invalid connection
ENOMEM	Memory copy exception
EIO	Incorrect connection type obtained based on the socket descriptor
EOPNOTSUPP	Unsupported message type

## sendto\(\) ``` ssize_t sendto (int fd, const void * buf, size_t len, int flags, const struct [sockaddr](sockaddr.md) * addr, [socklen_t](UTILS.md#ga531675af4e35aaa1cc9aeefa6cc2ccc4) alen ) ``` **Description:** Sends data to another socket. **Parameters:**

Name	Description
fd	Indicates the socket descriptor.
buf	Indicates the pointer to a buffer for storing the data to be sent.
len	Indicates the length of the buffer pointed to by buf.
flags	Indicates the socket flags. This parameter has the following values: MSG_DONTWAIT: enables the non-blocking operation. MSG_MORE: indicates that more messages are to be sent. MSG_NOSIGNAL: indicates that no signals are generated.
addr	Indicates the pointer to the destination network address.
alen	Indicates the length of the destination network address.

**Returns:** Returns the length of the sent data if the operation is successful; returns **-1** and sets **errno** to a value in the following table if the operation fails.

errno	Description
EINVAL	Invalid input parameter
EBADF	Invalid socket or socket status exception
EDESTADDRREQ	Invalid connection
ENOMEM	Memory copy exception
EOPNOTSUPP	Unsupported message type
ENOTCONN	Socket not connected
EIO	Incorrect connection type obtained based on the socket descriptor

## setprotoent\(\) ``` void setprotoent (int stayopen) ``` **Description:** Opens a connection to the database and sets the next entry to the first entry. **Parameters:**

Name	Description
stayopen	Reserved for interface compatibility (not used currently).

**Attention:** The **stayopen** parameter does not take effect. It is equivalent to nonzero for [getprotoent](NET.md#gaca0da70657afbc3e723990bb229deec3) and zero for [getprotobyname](NET.md#ga83ac8a97dd9d895cda658af3aa46fd55) and **getprotobynumbmer**. ## setsockopt\(\) ``` int setsockopt (int fd, int level, int optname, const void * optval, [socklen_t](UTILS.md#ga531675af4e35aaa1cc9aeefa6cc2ccc4) optlen ) ``` **Description:** Sets the socket options. **Parameters:**

Name	Description
fd	Indicates the socket descriptor.
level	Indicates the protocol level at which the option resides. Only SOL_SOCKET is supported.
optname	Indicates the socket options to set, which has the following values: SO_BROADCAST: permits sending and receiving broadcast messages. SO_RCVTIMEO: defines the data receiving timeout interval. SO_RCVBUF: defines the size of the socket receiving buffer, in bytes. SO_DONTROUTE: prohibits messages from being sent via a gateway. SO_BINDTODEVICE: binds this socket to a particular device.
optval	Indicates the pointer to the option data.
optlen	Indicates the size of the buffer pointed to by optval.

**Returns:** Returns **0** if the operation is successful; returns **-1** and sets **errno** to a value in the following table if the operation fails.

errno	Description
EINVAL	Small optlen
EBADF	Invalid socket or socket status exception
EFAULT	The input parameter is a null pointer.
ENOBUFS	Retrieved length exception
ENOMEM	Memory copy exception

## shutdown\(\) ``` int shutdown (int sockfd, int how ) ``` **Description:** Shuts down a socket. **Parameters:**

Name	Description
sockfd	Indicates the socket descriptor.
how	Indicates how to shut down the socket. You can disable either receptions by SHUT_RD or transmissions by SHUT_WR, or both by SHUT_RDWR.

**Returns:** Returns **0** if the operation is successful; returns **-1** and sets **errno** to a value in the following table if the operation fails.

errno	Description
EINVAL	Invalid input parameter
ENOTCONN	Socket not connected
ENOMEM	Memory copy exception
EIO	Incorrect connection type obtained based on the socket descriptor

## socket\(\) ``` int socket (int domain, int type, int protocol ) ``` **Description:** Creates a socket and returns its descriptor. **Parameters:**

Name	Description
domain	Indicates the socket family.
type	Indicates the socket type.
protocol	Indicates the socket protocol.

**Attention:** The domain can only be [AF\_INET](NET.md#ga9930604d0e32588eae76f43ca38e7826) or [AF\_INET6](NET.md#gaa03706b2738b9a58d4985dfbe99e1bac). The socket type can only be [SOCK\_RAW](NET.md#ga346f84e37c42f88e91e7304c3d77fde8), [SOCK\_DGRAM](NET.md#ga4db8b9a846c67404db0b6f014f9a9fdf), or [SOCK\_STREAM](NET.md#ga249394484f9410a2e3f8eba24657feb9). **Returns:** Returns the descriptor for the new socket if the operation is successful; returns **-1** and sets **errno** to a value in the following table if the operation fails.

errno	Description
EAFNOSUPPORT	Invalid socket domain
ESOCKTNOSUPPORT	Unsupported socket domain
EPROTONOSUPPORT	Unsupported protocol
EINVAL	Invalid input parameter
ENOBUFS	Connection setup error
ENFILE	File table addition exception