buffer

The buffer function is used to create a buffer object to represent raw memory, an array of POD elements, a vector of POD elements, or a std::string.

Create a new modifiable buffer from an existing buffer.

mutable_buffer buffer(
    const mutable_buffer & b);
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mutable_buffer buffer(
    const mutable_buffer & b,
    std::size_t max_size_in_bytes);
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Create a new non-modifiable buffer from an existing buffer.

const_buffer buffer(
    const const_buffer & b);
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const_buffer buffer(
    const const_buffer & b,
    std::size_t max_size_in_bytes);
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Create a new modifiable buffer that represents the given memory range.

mutable_buffer buffer(
    void * data,
    std::size_t size_in_bytes);
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Create a new non-modifiable buffer that represents the given memory range.

const_buffer buffer(
    const void * data,
    std::size_t size_in_bytes);
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Create a new modifiable buffer that represents the given POD array.

template<
    typename PodType,
    std::size_t N>
mutable_buffer buffer(
    PodType((&data)[N]);
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template<
    typename PodType,
    std::size_t N>
mutable_buffer buffer(
    PodType((&data)[N],
    std::size_t max_size_in_bytes);
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Create a new non-modifiable buffer that represents the given POD array.

template<
    typename PodType,
    std::size_t N>
const_buffer buffer(
    const PodType((&data)[N]);
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template<
    typename PodType,
    std::size_t N>
const_buffer buffer(
    const PodType((&data)[N],
    std::size_t max_size_in_bytes);
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Create a new modifiable buffer that represents the given POD array.

template<
    typename PodType,
    std::size_t N>
mutable_buffer buffer(
    boost::array< PodType, N > & data);
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template<
    typename PodType,
    std::size_t N>
mutable_buffer buffer(
    boost::array< PodType, N > & data,
    std::size_t max_size_in_bytes);
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Create a new non-modifiable buffer that represents the given POD array.

template<
    typename PodType,
    std::size_t N>
const_buffer buffer(
    boost::array< const PodType, N > & data);
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template<
    typename PodType,
    std::size_t N>
const_buffer buffer(
    boost::array< const PodType, N > & data,
    std::size_t max_size_in_bytes);
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Create a new modifiable buffer that represents the given POD array.

template<
    typename PodType,
    std::size_t N>
mutable_buffer buffer(
    std::array< PodType, N > & data);
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template<
    typename PodType,
    std::size_t N>
mutable_buffer buffer(
    std::array< PodType, N > & data,
    std::size_t max_size_in_bytes);
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Create a new non-modifiable buffer that represents the given POD array.

template<
    typename PodType,
    std::size_t N>
const_buffer buffer(
    std::array< const PodType, N > & data);
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template<
    typename PodType,
    std::size_t N>
const_buffer buffer(
    std::array< const PodType, N > & data,
    std::size_t max_size_in_bytes);
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Create a new modifiable buffer that represents the given POD vector.

template<
    typename PodType,
    typename Allocator>
mutable_buffer buffer(
    std::vector< PodType, Allocator > & data);
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template<
    typename PodType,
    typename Allocator>
mutable_buffer buffer(
    std::vector< PodType, Allocator > & data,
    std::size_t max_size_in_bytes);
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Create a new non-modifiable buffer that represents the given POD vector.

template<
    typename PodType,
    typename Allocator>
const_buffer buffer(
    const std::vector< PodType, Allocator > & data);
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template<
    typename PodType,
    typename Allocator>
const_buffer buffer(
    const std::vector< PodType, Allocator > & data,
    std::size_t max_size_in_bytes);
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Create a new modifiable buffer that represents the given string.

template<
    typename Elem,
    typename Traits,
    typename Allocator>
mutable_buffer buffer(
    std::basic_string< Elem, Traits, Allocator > & data);
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template<
    typename Elem,
    typename Traits,
    typename Allocator>
mutable_buffer buffer(
    std::basic_string< Elem, Traits, Allocator > & data,
    std::size_t max_size_in_bytes);
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Create a new non-modifiable buffer that represents the given string.

template<
    typename Elem,
    typename Traits,
    typename Allocator>
const_buffer buffer(
    const std::basic_string< Elem, Traits, Allocator > & data);
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template<
    typename Elem,
    typename Traits,
    typename Allocator>
const_buffer buffer(
    const std::basic_string< Elem, Traits, Allocator > & data,
    std::size_t max_size_in_bytes);
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Create a new non-modifiable buffer that represents the given string_view.

template<
    typename Elem,
    typename Traits>
const_buffer buffer(
    basic_string_view< Elem, Traits > data);
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Create a new non-modifiable buffer that represents the given string.

template<
    typename Elem,
    typename Traits>
const_buffer buffer(
    basic_string_view< Elem, Traits > data,
    std::size_t max_size_in_bytes);
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Create a new modifiable buffer from a contiguous container.

template<
    typename T>
mutable_buffer buffer(
    T & data,
    constraint_t< is_contiguous_iterator< typename T::iterator >::value, defaulted_constraint >  = defaulted_constraint(),
    constraint_t< !is_convertible< T, const_buffer >::value, defaulted_constraint >  = defaulted_constraint(),
    constraint_t< !is_convertible< T, mutable_buffer >::value, defaulted_constraint >  = defaulted_constraint(),
    constraint_t< !is_const< remove_reference_t< typename std::iterator_traits< typename T::iterator >::reference > >::value, defaulted_constraint >  = defaulted_constraint());
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template<
    typename T>
mutable_buffer buffer(
    T & data,
    std::size_t max_size_in_bytes,
    constraint_t< is_contiguous_iterator< typename T::iterator >::value, defaulted_constraint >  = defaulted_constraint(),
    constraint_t< !is_convertible< T, const_buffer >::value, defaulted_constraint >  = defaulted_constraint(),
    constraint_t< !is_convertible< T, mutable_buffer >::value, defaulted_constraint >  = defaulted_constraint(),
    constraint_t< !is_const< remove_reference_t< typename std::iterator_traits< typename T::iterator >::reference > >::value, defaulted_constraint >  = defaulted_constraint());
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Create a new non-modifiable buffer from a contiguous container.

template<
    typename T>
const_buffer buffer(
    T & data,
    constraint_t< is_contiguous_iterator< typename T::iterator >::value, defaulted_constraint >  = defaulted_constraint(),
    constraint_t< !is_convertible< T, const_buffer >::value, defaulted_constraint >  = defaulted_constraint(),
    constraint_t< !is_convertible< T, mutable_buffer >::value, defaulted_constraint >  = defaulted_constraint(),
    constraint_t< is_const< remove_reference_t< typename std::iterator_traits< typename T::iterator >::reference > >::value, defaulted_constraint >  = defaulted_constraint());
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template<
    typename T>
const_buffer buffer(
    T & data,
    std::size_t max_size_in_bytes,
    constraint_t< is_contiguous_iterator< typename T::iterator >::value, defaulted_constraint >  = defaulted_constraint(),
    constraint_t< !is_convertible< T, const_buffer >::value, defaulted_constraint >  = defaulted_constraint(),
    constraint_t< !is_convertible< T, mutable_buffer >::value, defaulted_constraint >  = defaulted_constraint(),
    constraint_t< is_const< remove_reference_t< typename std::iterator_traits< typename T::iterator >::reference > >::value, defaulted_constraint >  = defaulted_constraint());
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template<
    typename T>
const_buffer buffer(
    const T & data,
    constraint_t< is_contiguous_iterator< typename T::const_iterator >::value, defaulted_constraint >  = defaulted_constraint(),
    constraint_t< !is_convertible< T, const_buffer >::value, defaulted_constraint >  = defaulted_constraint(),
    constraint_t< !is_convertible< T, mutable_buffer >::value, defaulted_constraint >  = defaulted_constraint());
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template<
    typename T>
const_buffer buffer(
    const T & data,
    std::size_t max_size_in_bytes,
    constraint_t< is_contiguous_iterator< typename T::const_iterator >::value, defaulted_constraint >  = defaulted_constraint(),
    constraint_t< !is_convertible< T, const_buffer >::value, defaulted_constraint >  = defaulted_constraint(),
    constraint_t< !is_convertible< T, mutable_buffer >::value, defaulted_constraint >  = defaulted_constraint());
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Obtain a buffer representing the entire registered buffer.

mutable_registered_buffer buffer(
    const mutable_registered_buffer & b);
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const_registered_buffer buffer(
    const const_registered_buffer & b);
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Obtain a buffer representing part of a registered buffer.

mutable_registered_buffer buffer(
    const mutable_registered_buffer & b,
    std::size_t n);
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const_registered_buffer buffer(
    const const_registered_buffer & b,
    std::size_t n);
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A buffer object represents a contiguous region of memory as a 2-tuple consisting of a pointer and size in bytes. A tuple of the form {void*, size_t} specifies a mutable (modifiable) region of memory. Similarly, a tuple of the form {const void*, size_t} specifies a const (non-modifiable) region of memory. These two forms correspond to the classes mutable_buffer and const_buffer, respectively. To mirror C++'s conversion rules, a mutable_buffer is implicitly convertible to a const_buffer, and the opposite conversion is not permitted.

The simplest use case involves reading or writing a single buffer of a specified size:

sock.send(boost::asio::buffer(data, size));

In the above example, the return value of buffer meets the requirements of the ConstBufferSequence concept so that it may be directly passed to the socket's write function. A buffer created for modifiable memory also meets the requirements of the MutableBufferSequence concept.

An individual buffer may be created from a builtin array, std::vector, std::array or boost::array of POD elements. This helps prevent buffer overruns by automatically determining the size of the buffer:

char d1[128];
size_t bytes_transferred = sock.receive(boost::asio::buffer(d1));

std::vector<char> d2(128);
bytes_transferred = sock.receive(boost::asio::buffer(d2));

std::array<char, 128> d3;
bytes_transferred = sock.receive(boost::asio::buffer(d3));

boost::array<char, 128> d4;
bytes_transferred = sock.receive(boost::asio::buffer(d4));

In all three cases above, the buffers created are exactly 128 bytes long. Note that a vector is never automatically resized when creating or using a buffer. The buffer size is determined using the vector's size() member function, and not its capacity.

Accessing Buffer Contents

The contents of a buffer may be accessed using the data() and size() member functions:

boost::asio::mutable_buffer b1 = ...;
std::size_t s1 = b1.size();
unsigned char* p1 = static_cast<unsigned char*>(b1.data());

boost::asio::const_buffer b2 = ...;
std::size_t s2 = b2.size();
const void* p2 = b2.data();

The data() member function permits violations of type safety, so uses of it in application code should be carefully considered.

For convenience, a buffer_size function is provided that works with both buffers and buffer sequences (that is, types meeting the ConstBufferSequence or MutableBufferSequence type requirements). In this case, the function returns the total size of all buffers in the sequence.

Buffer Copying

The buffer_copy function may be used to copy raw bytes between individual buffers and buffer sequences.

In particular, when used with the buffer_size function, the buffer_copy function can be used to linearise a sequence of buffers. For example:

vector<const_buffer> buffers = ...;

vector<unsigned char> data(boost::asio::buffer_size(buffers));
boost::asio::buffer_copy(boost::asio::buffer(data), buffers);

Note that buffer_copy is implemented in terms of memcpy, and consequently it cannot be used to copy between overlapping memory regions.

Buffer Invalidation

A buffer object does not have any ownership of the memory it refers to. It is the responsibility of the application to ensure the memory region remains valid until it is no longer required for an I/O operation. When the memory is no longer available, the buffer is said to have been invalidated.

For the buffer overloads that accept an argument of type std::vector, the buffer objects returned are invalidated by any vector operation that also invalidates all references, pointers and iterators referring to the elements in the sequence (C++ Std, 23.2.4)

For the buffer overloads that accept an argument of type std::basic_string, the buffer objects returned are invalidated according to the rules defined for invalidation of references, pointers and iterators referring to elements of the sequence (C++ Std, 21.3).

Buffer Arithmetic

Buffer objects may be manipulated using simple arithmetic in a safe way which helps prevent buffer overruns. Consider an array initialised as follows:

boost::array<char, 6> a = { 'a', 'b', 'c', 'd', 'e' };

A buffer object b1 created using:

b1 = boost::asio::buffer(a);

represents the entire array, { 'a', 'b', 'c', 'd', 'e' }. An optional second argument to the buffer function may be used to limit the size, in bytes, of the buffer:

b2 = boost::asio::buffer(a, 3);

such that b2 represents the data { 'a', 'b', 'c' }. Even if the size argument exceeds the actual size of the array, the size of the buffer object created will be limited to the array size.

An offset may be applied to an existing buffer to create a new one:

b3 = b1 + 2;

where b3 will set to represent { 'c', 'd', 'e' }. If the offset exceeds the size of the existing buffer, the newly created buffer will be empty.

Both an offset and size may be specified to create a buffer that corresponds to a specific range of bytes within an existing buffer:

b4 = boost::asio::buffer(b1 + 1, 3);

so that b4 will refer to the bytes { 'b', 'c', 'd' }.

Buffers and Scatter-Gather I/O

To read or write using multiple buffers (i.e. scatter-gather I/O), multiple buffer objects may be assigned into a container that supports the MutableBufferSequence (for read) or ConstBufferSequence (for write) concepts:

char d1[128];
std::vector<char> d2(128);
boost::array<char, 128> d3;

boost::array<mutable_buffer, 3> bufs1 = {
  boost::asio::buffer(d1),
  boost::asio::buffer(d2),
  boost::asio::buffer(d3) };
bytes_transferred = sock.receive(bufs1);

std::vector<const_buffer> bufs2;
bufs2.push_back(boost::asio::buffer(d1));
bufs2.push_back(boost::asio::buffer(d2));
bufs2.push_back(boost::asio::buffer(d3));
bytes_transferred = sock.send(bufs2);

Buffer Literals

The _buf literal suffix, defined in namespace boost::asio::buffer_literals, may be used to create const_buffer objects from string, binary integer, and hexadecimal integer literals. For example:

using namespace boost::asio::buffer_literals;

boost::asio::const_buffer b1 = "hello"_buf;
boost::asio::const_buffer b2 = 0xdeadbeef_buf;
boost::asio::const_buffer b3 = 0x0123456789abcdef0123456789abcdef_buf;
boost::asio::const_buffer b4 = 0b1010101011001100_buf;

Note that the memory associated with a buffer literal is valid for the lifetime of the program. This means that the buffer can be safely used with asynchronous operations.

Requirements

Header: boost/asio/buffer.hpp

Convenience header: boost/asio.hpp