int recv( SOCKET s, char FAR *buf, int len, int flags ); 中的flags 取 0是什么意思 ？
最新回答
青柠之恋
2023-12-20 12:54:40
而我们一般用的时候都是置零
可能楼主想多了
flag有几个特殊参数 比如MSG_OOB MSG_BONTROUTE
这些都表示recv在接受数据时要遵循特殊规则，
所以当flag=0时 就默认是普通接受数据 模式
也就是：从接口s 缓存区buf读取len字节的数据 这就这样 没有什么特殊意思
像个路人
2023-04-17 22:05:54
recv Function
The recv function receives data from a connected or bound socket.
int recv(
__in SOCKET s,
__out char* buf,
__in int len,
__in int flags
);
Parameters
s
The descriptor that identifies a connected socket.
buf
The buffer for incoming data.
len
The length, in bytes, of the buf parameter.
flags
A pointer to flags that influences the behavior of this function. See remarks below.
其中：
Remarks
The recv function is used to read incoming data on connection-oriented sockets, or connectionless sockets. When using a connection-oriented protocol, the sockets must be connected before calling recv. When using a connectionless protocol, the sockets must be bound before calling recv.
The local address of the socket must be known. For server applications, use an explicit bind function or an implicit accept or WSAAccept function. Explicit binding is discouraged for client applications. For client applications, the socket can become bound implicitly to a local address using connect, WSAConnect, sendto, WSASendTo, or WSAJoinLeaf.
For connected or connectionless sockets, the recv function restricts the addresses from which received messages are accepted. The function only returns messages from the remote address specified in the connection. Messages from other addresses are (silently) discarded.
For connection-oriented sockets (type SOCK_STREAM for example), calling recv will return as much data as is currently available—up to the size of the buffer specified. If the socket has been configured for in-line reception of OOB data (socket option SO_OOBINLINE) and OOB data is yet unread, only OOB data will be returned. The application can use the ioctlsocket or WSAIoctlSIOCATMARK command to determine whether any more OOB data remains to be read.
For connectionless sockets (type SOCK_DGRAM or other message-oriented sockets), data is extracted from the first enqueued datagram (message) from the destination address specified by the connect function.
If the datagram or message is larger than the buffer specified, the buffer is filled with the first part of the datagram, and recv generates the error WSAEMSGSIZE. For unreliable protocols (for example, UDP) the excess data is lost; for reliable protocols, the data is retained by the service provider until it is successfully read by calling recv with a large enough buffer.
If no incoming data is available at the socket, the recv call blocks and waits for data to arrive according to the blocking rules defined for WSARecv with the MSG_PARTIAL flag not set unless the socket is nonblocking. In this case, a value of SOCKET_ERROR is returned with the error code set to WSAEWOULDBLOCK. The select, WSAAsyncSelect, or WSAEventSelect functions can be used to determine when more data arrives.
If the socket is connection oriented and the remote side has shut down the connection gracefully, and all data has been received, a recv will complete immediately with zero bytes received. If the connection has been reset, a recv will fail with the error WSAECONNRESET.
Note When issuing a blocking Winsock call, such as send, recv, select, accept, or connect function calls, Winsock may need to wait for a network event before the call can complete. Winsock performs an alertable wait in this situation, which can be interrupted by an asynchronous procedure call (APC) scheduled on the same thread, and thereby create unspecified results. Do not issue blocking Winsock function calls without being certain that the current thread is not waiting inside another blocking Winsock function call; doing so results in unpredictable behavior.
The flags parameter can be used to influence the behavior of the function invocation beyond the options specified for the associated socket. The semantics of this function are determined by the socket options and the flags parameter. The latter is constructed by using the bitwise OR operator with any of the following values.
Value Meaning
MSG_PEEK Peeks at the incoming data. The data is copied into the buffer, but is not removed from the input queue. The function subsequently returns the amount of data that can be read in a single call to the recv (or recvfrom) function, which may not be the same as the total amount of data queued on the socket. The amount of data that can actually be read in a single call to the recv (or recvfrom) function is limited to the data size written in the send or sendto function call.
MSG_OOB Processes Out Of Band (OOB) data.
MSG_WAITALL The receive request will complete only when one of the following events occurs:
The buffer supplied by the caller is completely full.
The connection has been closed.
The request has been canceled.
Note that if the underlying transport does not support MSG_WAITALL, or if the socket is in a non-blocking mode, then this call will fail with WSAEOPNOTSUPP. Also, if MSG_WAITALL is specified along with MSG_OOB, MSG_PEEK, or MSG_PARTIAL, then this call will fail with WSAEOPNOTSUPP. This flag is not supported on datagram sockets or message-oriented CO sockets.
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