A type X meets the SyncWriteStream requirements if it satisfies the requirements listed below.
In the table below, a denotes a value of type X, cb denotes a (possibly const) value of a type satisfying the ConstBufferSequence ([buffer.reqmts.constbuffersequence]) requirements, and ec denotes an object of type error_code.
| operation | type | semantics, pre/post-conditions |
| a.write_some(cb) a.write_some(cb,ec) | size_t |
Meets the requirements for a write operation ([buffer.reqmts.read.write]). If buffer_size(cb) > 0, writes one or more bytes of data to the stream a from the buffer sequence cb. If successful, sets ec such that !ec is true, and returns the number of bytes written. If an error occurred, sets ec such that !!ec is true, and returns 0. If buffer_size(cb) == 0, the operation shall not block. Sets ec such that !ec is true, and returns 0. |