SDL Wiki
(This function is part of SDL_net, a separate library from SDL.)


Receive bytes that a remote system sent to a stream socket.

Header File

Defined in <SDL3_net/SDL_net.h>


int SDLNet_ReadFromStreamSocket(SDLNet_StreamSocket *sock, void *buf, int buflen);

Function Parameters

SDLNet_StreamSocket * sock the stream socket to receive data from.
void * buf a pointer to a buffer where received data will be collected.
int buflen the size of the buffer pointed to by buf, in bytes. This is the maximum that will be read from the stream socket.

Return Value

(int) Returns number of bytes read from the stream socket (which can be less than buflen or zero if none available), -1 on failure; call SDL_GetError() for details.


Stream sockets are reliable, which means data sent over them will arrive in the order it was transmitted, and the system will retransmit data as necessary to ensure its delivery. Which is to say, short of catastrophic failure, data will arrive, possibly with severe delays. Also, "catastrophic failure" isn't an uncommon event.

(This is opposed to Datagram sockets, which send chunks of data that might arrive in any order, or not arrive at all, but you never wait for missing chunks to show up.)

Stream sockets are bidirectional; you can read and write from the same stream, and the other end of the connection can, too.

This function returns data that has arrived for the stream socket that hasn't been read yet. Data is provided in the order it was sent on the remote side. This function may return less data than requested, depending on what is available at the time, and also the app isn't required to read all available data at once.

This call never blocks; if no new data isn't available at the time of the call, it returns 0 immediately. The caller can try again later.

If the connection has failed (remote side dropped us, or one of a million other networking failures occurred), this function will report failure by returning -1. Stream sockets only report failure for unrecoverable conditions; once a stream socket fails, you should assume it is no longer usable and should destroy it with SDL_DestroyStreamSocket().

Thread Safety

You should not operate on the same socket from multiple threads at the same time without supplying a serialization mechanism. However, different threads may access different sockets at the same time without problems.


This function is available since SDL_Net 3.0.0.

See Also

CategoryAPI, CategoryAPIFunction

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