basic_streambuf

Automatically resizable buffer class based on std::streambuf.

template<
    typename Allocator = std::allocator<char>>
class basic_streambuf :
  public std::streambuf,
  noncopyable

Types

Name	Description
const_buffers_type	The type used to represent the input sequence as a list of buffers.
mutable_buffers_type	The type used to represent the output sequence as a list of buffers.

Member Functions

Name	Description
basic_streambuf [constructor]	Construct a basic_streambuf object.
capacity	Get the current capacity of the basic_streambuf.
commit	Move characters from the output sequence to the input sequence.
consume	Remove characters from the input sequence.
data	Get a list of buffers that represents the input sequence.
max_size	Get the maximum size of the basic_streambuf.
prepare	Get a list of buffers that represents the output sequence, with the given size.
size	Get the size of the input sequence.

Protected Member Functions

Name	Description
overflow	Override std::streambuf behaviour.
reserve
underflow	Override std::streambuf behaviour.

The basic_streambuf class is derived from std::streambuf to associate the streambuf's input and output sequences with one or more character arrays. These character arrays are internal to the basic_streambuf object, but direct access to the array elements is provided to permit them to be used efficiently with I/O operations. Characters written to the output sequence of a basic_streambuf object are appended to the input sequence of the same object.

The basic_streambuf class's public interface is intended to permit the following implementation strategies:

A single contiguous character array, which is reallocated as necessary to accommodate changes in the size of the character sequence. This is the implementation approach currently used in Asio.
A sequence of one or more character arrays, where each array is of the same size. Additional character array objects are appended to the sequence to accommodate changes in the size of the character sequence.
A sequence of one or more character arrays of varying sizes. Additional character array objects are appended to the sequence to accommodate changes in the size of the character sequence.

The constructor for basic_streambuf accepts a size_t argument specifying the maximum of the sum of the sizes of the input sequence and output sequence. During the lifetime of the basic_streambuf object, the following invariant holds:

size() <= max_size()

Any member function that would, if successful, cause the invariant to be violated shall throw an exception of class std::length_error.

The constructor for basic_streambuf takes an Allocator argument. A copy of this argument is used for any memory allocation performed, by the constructor and by all member functions, during the lifetime of each basic_streambuf object.

Examples

Writing directly from an streambuf to a socket:

boost::asio::streambuf b;
std::ostream os(&b);
os << "Hello, World!\n";

// try sending some data in input sequence
size_t n = sock.send(b.data());

b.consume(n); // sent data is removed from input sequence

Reading from a socket directly into a streambuf:

boost::asio::streambuf b;

// reserve 512 bytes in output sequence
boost::asio::streambuf::mutable_buffers_type bufs = b.prepare(512);

size_t n = sock.receive(bufs);

// received data is "committed" from output sequence to input sequence
b.commit(n);

std::istream is(&b);
std::string s;
is >> s;

Requirements

Header: boost/asio/basic_streambuf.hpp

Convenience header: boost/asio.hpp