Buffer-oriented synchronous random-access read device requirements

In the table below, a denotes a synchronous random-access read device object, o denotes an offset of type boost::uint64_t, mb denotes an object satisfying mutable buffer sequence requirements, and ec denotes an object of type error_code.

Table 29. Buffer-oriented synchronous random-access read device requirements

operation	type	semantics, pre/post-conditions
`a.read_some_at(o, mb);`	`size_t`	Equivalent to: error_code ec; size_t s = a.read_some_at(o, mb, ec); if (ec) throw system_error(ec); return s;
`a.read_some_at(o, mb, ec);`	`size_t`	Reads one or more bytes of data from the device `a` at offset `o`. The mutable buffer sequence `mb` specifies memory where the data should be placed. The `read_some_at` operation shall always fill a buffer in the sequence completely before proceeding to the next. If successful, returns the number of bytes read 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 `mb` is `0`, the function shall return `0` immediately.

operation

type

semantics, pre/post-conditions

a.read_some_at(o, mb);

size_t

Equivalent to:

error_code ec;
size_t s = a.read_some_at(o, mb, ec);
if (ec) throw system_error(ec);
return s;

a.read_some_at(o, mb, ec);

size_t

Reads one or more bytes of data from the device a at offset o.

The mutable buffer sequence mb specifies memory where the data should be placed. The read_some_at operation shall always fill a buffer in the sequence completely before proceeding to the next.

If successful, returns the number of bytes read 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 mb is 0, the function shall return 0 immediately.