socket

SOCKET socket(
  int af,
  int type,
  int protocol
);

Parameters

Parameter	Description
af	The address family. This parameter can be one of the following: AF_INET: IPv4 Internet address family. AF_INET6: IPv6 Internet address family. AF_UNSPEC: Unspecified address family.
type	The socket type, which determines the semantics of communication by this socket. This parameter can be one of the following values defined in the Winsock header file: SOCK_STREAM: A socket that provides two-way connection-based byte streams. A duplicate address and port can be used by only one process at a time. TCP is the typical protocol for the SOCK_STREAM type. SOCK_DGRAM: A socket that supports datagrams, which are connectionless based messages. Datagram sockets are not reliable and do not guarantee delivery or that datagrams will arrive in the order in which they were sent. UDP is the typical protocol for the SOCK_DGRAM type. SOCK_RAW: A socket that provides raw network protocol access.
protocol	The protocol to be used with the socket. The valid values for the protocol parameter depend on the address family specified in the af parameter. If af is AF_INET or AF_INET6, this parameter can be IPPROTO_TCP, IPPROTO_UDP, or 0. If you specify 0, the Winsock provider will use the default protocol for the requested socket type. The most common use is to specify 0 to let the system choose the default protocol for the specified socket type.

Return Value

If no error occurs, socket returns a descriptor for the newly created socket. This descriptor is a SOCKET value, which is an integer type. This value can be used in subsequent Winsock function calls to identify this socket instance.

If an error occurs, socket returns INVALID_SOCKET. To get extended error information, call WSAGetLastError.

Remarks

The socket function creates a socket that is bound to a specific transport service provider. The transport service provider is specified by the af, type, and protocol parameters.

If the protocol parameter is set to 0, the Winsock service provider will use the default protocol associated with the requested socket type. For example, if af is AF_INET and type is SOCK_STREAM, setting protocol to 0 will select TCP.

The socket function is used to create endpoints for communication. The returned socket descriptor can then be used to establish connections, send or receive data, and manage network communication.

Example

#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdio.h>

// Link with Ws2_32.lib
#pragma comment(lib, "Ws2_32.lib")

int main() {
    WSADATA wsaData;
    SOCKET sockfd = INVALID_SOCKET;
    int iResult;

    // Initialize Winsock
    iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
    if (iResult != 0) {
        printf("WSAStartup failed: %d\n", iResult);
        return 1;
    }

    // Create a TCP/IP socket
    sockfd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (sockfd == INVALID_SOCKET) {
        printf("socket failed: %d\n", WSAGetLastError());
        WSACleanup();
        return 1;
    }

    printf("Socket created successfully.\n");

    // You would typically bind, listen, accept, or connect here.
    // For this example, we'll just close the socket.

    iResult = closesocket(sockfd);
    if (iResult == SOCKET_ERROR) {
        printf("closesocket failed: %d\n", WSAGetLastError());
        WSACleanup();
        return 1;
    }

    printf("Socket closed successfully.\n");

    // Clean up Winsock
    WSACleanup();
    return 0;
}
            

See Also