WSANtohl function (winsock2.h)

The WSANtohl function converts a u_long from network byte order to host byte order.


int WSAAPI WSANtohl(
  [in]  SOCKET s,
  [in]  u_long netlong,
  [out] u_long *lphostlong


[in] s

A descriptor identifying a socket.

[in] netlong

A 32-bit number in network byte order.

[out] lphostlong

A pointer to a 32-bit number to receive the number in host byte order.

Return value

If no error occurs, WSANtohl returns zero. Otherwise, a value of SOCKET_ERROR is returned, and a specific error code can be retrieved by calling WSAGetLastError.

Error code Meaning
A successful WSAStartup call must occur before using this function.
The network subsystem has failed.
The descriptor is not a socket.
The lphostlong parameter is NULL or the address pointed to is not completely contained in a valid part of the user address space.


The WSANtohl function takes a 32-bit number in network byte order and returns a 32-bit number in host byte order in the 32-bit number pointed to by the lphostlong parameter. The socket passed in the s parameter is used to determine the network byte order required based on the Winsock catalog protocol entry associated with the socket. This feature supports Winsock providers that use different network byte orders.

If the socket is for the AF_INET or AF_INET6 address family, the WSANtohl function can be used to convert an IPv4 address in network byte order to the IPv4 address in host byte order. This function does not do any checking to determine if the netlong parameter is a valid IPv4 address.

The WSANtohl function requires that the Winsock DLL has previously been loaded with a successful call to the WSAStartup function. For use with the AF_INET or AF_INET6 family, the ntohl function does not require that the Winsock DLL be loaded.

Windows Phone 8: This function is supported for Windows Phone Store apps on Windows Phone 8 and later.

Windows 8.1 and Windows Server 2012 R2: This function is supported for Windows Store apps on Windows 8.1, Windows Server 2012 R2, and later.


Minimum supported client Windows 8.1, Windows Vista [desktop apps | UWP apps]
Minimum supported server Windows Server 2003 [desktop apps | UWP apps]
Target Platform Windows
Header winsock2.h
Library Ws2_32.lib
DLL Ws2_32.dll

See also





Winsock Functions

Winsock Reference