DynamicBuffer

A DynamicBuffer represents memory storage that may be automatically resized as required, where the memory is divided into an input sequence followed by an output sequence. 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, such as the send or receive operations of a socket. Data written to the output sequence of a dynamic buffer object is appended to the input sequence of the same object.

Related Identifiers

is_dynamic_buffer

Requirements

  • D denotes a dynamic buffer class.

  • a denotes a value of type D.

  • c denotes a (possibly const) value of type D.

  • n denotes a value of type std::size_t.

  • T denotes a type meeting the requirements for ConstBufferSequence.

  • U denotes a type meeting the requirements for MutableBufferSequence.

Expression Type Semantics, Pre/Post-conditions

D::const_buffers_type

T

This type represents the memory associated with the input sequence.

D::mutable_buffers_type

U

This type represents the memory associated with the output sequence.

c.size()

std::size_t

Returns the size, in bytes, of the input sequence.

c.max_size()

std::size_t

Returns the permitted maximum of the sum of the sizes of the input sequence and output sequence.

c.capacity()

std::size_t

Returns the maximum sum of the sizes of the input sequence and output sequence that the dynamic buffer can hold without requiring reallocation.

c.data()

D::const_buffers_type

Returns a constant buffer sequence u that represents the memory associated with the input sequence, and where buffer_size(u) == size().

a.prepare(n)

D::mutable_buffers_type

Returns a mutable buffer sequence u representing the output sequence, 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().

a.commit(n)

Appends n bytes from the start of the output sequence to the end of the input sequence. The remainder of the output sequence is discarded. If n is greater than the size of the output sequence, the entire output sequence is appended to the input sequence. All constant or mutable buffer sequences previously obtained using data() or prepare() are invalidated.

a.consume(n)

Removes n bytes from beginning of the input sequence. If n is greater than the size of the input sequence, the entire input sequence is removed. All constant or mutable buffer sequences previously obtained using data() or prepare() are invalidated.

Example

#include <boost/buffers.hpp>

using namespace boost::buffers;

// Generic function that works with any DynamicBuffer
template<class DynamicBuffer>
void append_greeting(DynamicBuffer& db)
{
    char const* msg = "Hello!";
    std::size_t len = 6;

    // Prepare space in the output sequence
    auto dest = db.prepare(len);

    // Copy data into the prepared space
    copy(dest, const_buffer(msg, len));

    // Move data from output to input sequence
    db.commit(len);
}

int main()
{
    // Works with circular_buffer
    char storage1[64];
    circular_buffer cb(storage1, sizeof(storage1));
    append_greeting(cb);

    // Works with flat_buffer
    char storage2[64];
    flat_buffer fb(storage2, sizeof(storage2));
    append_greeting(fb);

    // Works with string_buffer
    std::string str;
    string_buffer sb(&str);
    append_greeting(sb);
}

Models

See Also

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