WSARecvEx - Sockets 2 Reference

Custom Search

WSARecvEx

This function is a Microsoft-specific extension to the Windows Sockets specification. For more information, see Microsoft Extensions and Windows Sockets 2.

The Windows Sockets WSARecvEx function is identical to the recv function, except the flags parameter is an in-out parameter. When a partial message is received while using datagram protocol, the MSG_PARTIAL bit is set in the flags parameter on return from the function.

int PASCAL FAR WSARecvEx (

SOCKET s,
char FAR * buf,
int len,
int *flags
);

Parameters
s

[in] A descriptor identifying a connected socket.

buf

[out] A buffer for the incoming data.

len

[in] The length of buf.

flags

[in/out] Specifies whether the message is fully or partiall received for datagram sockets.

Remarks
By default, for message-oriented transport protocols the Windows Sockets recv function receives a single message in each call to the function. This works fine for most cases, but there are two situations in which this is insufficient: when the application's data buffer is smaller than the message, and when the message is large and arrives in several pieces.

When the buffer is smaller than the data, as much of the message as will fit is copied into the user's buffer and recv returns with the error code WSAEMSGSIZE. A subsequent call to recv will get the next part of the message. Applications written for message-oriented transport protocols should be coded for this possibility if message sizing is not guaranteed by the application's data transfer protocol. If an application gets this error code, then the entire data buffer is filled with data.

It is more complicated when a very large message arrives a little at a time. For example, if an application sends a 1-megabyte message, the transport protocol must break up the message in order to send it over the physical network. It is theoretically possible for the transport protocol on the receiving side to buffer all the data in the message, but this would be quite expensive in terms of resources.

It would be better to allow a recv call to complete with only a partial message and some indication to the application that the data is only a partial message. However, the Windows Sockets recv function has only one output parameter: a pointer to the buffer for the incoming data. Therefore, Windows NT supplies the WSARecvEx function, which is identical to the recv function except that the flags parameter is an in-out parameter:

Return Values
On return from WSARecvEx, if a partial message was received, the MSG_PARTIAL bit is set in the flags parameter. If a complete message was received, MSG_PARTIAL is not set in flags. For a stream-oriented transport protocol, MSG_PARTIAL is never set on return from WSARecvEx; for stream transport protocols, this function behaves identically to the Windows Sockets recv function.

Last news from Greatis Software

    Nostalgia .Net     .Net is powerful, but not all-powerful, so sometimes we need to use Win32 API for our .Net applications. It's simple enough with Platform Invoke if you have Win32 skill, but we do not always have time to dig the ancient documentation, declare the special types that are compatible with Win32, find the values of the Win32's constants and so on. Nostalgia .Net offers several simple-to-use classes, and components that will allow you to forget about the headache of Win32 and just use the power of Win32 in your application the same way as you use the native. Net classes. More »

Recommended software for developers

    Ultimate Pack     Component pack for Delphi and C++ Builder that contains runtime form designer, runtime object inspector, print suite and much more for the very special price. More »

    Form Designer .Net     Unique runtime form design solution that allows to edit any form in .Net WinForms application at runtime with full source codes for only 300 euro! More »

    Print Suite .Net     Print Suite .Net is a set of components for easy printing texts, images and grids from your WinForms applications. Full C# source codes are available More »

    Gradient Controls .Net     Gradient Controls .Net offers controls with gradient background feature. Labels, panels and so on... Full C# source codes are available More »

    Greatis iGrid     iGrid plots drawing grid right over your desktop, so you can use it everywhere, with any drawing application without any special plugins for different graphic editors. More »

All the contacts and projects

Dmitry Vasiliev (just.dmitry)

More Online Helps

Win32 Programmer's Reference
Win32 Multimedia Programmer's Reference
OLE Programmer's Reference
Microsoft Windows Pen API Programmer's Reference
Microsoft Windows Sockets 2 Reference
Microsoft Windows Telephony API (TAPI) Programmer's Reference
Unix Manual Pages

greatis just4fun network