### Buffer-oriented synchronous write stream requirements

In the table below, `a` denotes a synchronous write stream object, `cb` denotes an object satisfying constant buffer sequence requirements, and `ec` denotes an object of type `error_code`.

Table 25. Buffer-oriented synchronous write stream requirements

operation | type | semantics, pre/post-conditions
--- | --- | ---
`a.write_some(cb);` | `size_t` | Equivalent to:
    error_code ec;
    size_t s = a.write_some(cb, ec);
    if (ec) throw system_error(ec);
    return s;
`a.write_some(cb, ec);` | `size_t` | Writes one or more bytes of data to the stream `a`. The constant buffer sequence `cb` specifies memory where the data to be written is located. The `write_some` operation shall always write a buffer in the sequence completely before proceeding to the next. If successful, returns the number of bytes written and sets `ec` such that `!ec` is true. If an error occurred, returns `0` and sets `ec` such that `!!ec` is true. If the total size of all buffers in the sequence `cb` is `0`, the function shall return `0` immediately.