A dynamic buffer encapsulates memory storage that may be automatically resized as required, where the memory is divided into two regions: readable bytes followed by writable bytes. These memory regions are internal to the dynamic buffer, but direct access to the elements is provided to permit them to be efficiently used with I/O operations. [ Note: Such as the send or receive operations of a socket. The readable bytes would be used as the constant buffer sequence for send, and the writable bytes used as the mutable buffer sequence for receive. — end note ] Data written to the writable bytes of a dynamic buffer object is appended to the readable bytes of the same object.
A type X meets the DynamicBuffer requirements if it satisfies the requirements of Destructible (C++ 2014 [destructible]) and MoveConstructible (C++ 2014 [moveconstructible]), as well as the additional requirements listed in Table [tab:buffer.reqmts.dynamicbuffer.requirements].
In Table [tab:buffer.reqmts.dynamicbuffer.requirements], x denotes a value of type X, x1 denotes a (possibly const) value of type X, and n denotes a (possibly const) value of type size_t.
| expression | type | assertion/note pre/post-conditions |
| X::const_buffers_type | type meeting ConstBufferSequence ([buffer.reqmts.constbuffersequence]) requirements. | This type represents the memory associated with the readable bytes. |
| X::mutable_buffers_type | type meeting MutableBufferSequence ([buffer.reqmts.constbuffersequence]) requirements. | This type represents the memory associated with the writable bytes. |
| x1.size() | size_t | Returns the number of readable bytes. |
| x1.max_size() | size_t | Returns the maximum number of bytes, both readable and writable, that can be held by x1. |
| x1.capacity() | size_t | Returns the maximum number of bytes, both readable and writable, that can be held by x1 without requiring reallocation. |
| x1.data() | X::const_buffers_type | Returns a constant buffer sequence u that represents the readable bytes, and where buffer_size(u) == size(). |
| x.prepare(n) | X::mutable_buffers_type |
Returns a mutable buffer sequence u representing the writable bytes, and where buffer_size(u) == n. The dynamic buffer reallocates memory as required. All constant or mutable buffer sequences previously obtained using data() or prepare() are invalidated. Throws: length_error if size() + n exceeds max_size(). |
| x.commit(n) | Appends n bytes from the start of the writable bytes to the end of the readable bytes. The remainder of the writable bytes are discarded. If n is greater than the number of writable bytes, all writable bytes are appended to the readable bytes. All constant or mutable buffer sequences previously obtained using data() or prepare() are invalidated. | |
| x.consume(n) | Removes n bytes from beginning of the readable bytes. If n is greater than the number of readable bytes, all readable bytes are removed. All constant or mutable buffer sequences previously obtained using data() or prepare() are invalidated. |