| 
							- //
 - // write_at.hpp
 - // ~~~~~~~~~~~~
 - //
 - // Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff dot com)
 - //
 - // Distributed under the Boost Software License, Version 1.0. (See accompanying
 - // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 - //
 - 
 - #ifndef ASIO_WRITE_AT_HPP
 - #define ASIO_WRITE_AT_HPP
 - 
 - #if defined(_MSC_VER) && (_MSC_VER >= 1200)
 - # pragma once
 - #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 - 
 - #include "asio/detail/config.hpp"
 - #include <cstddef>
 - #include "asio/async_result.hpp"
 - #include "asio/detail/cstdint.hpp"
 - #include "asio/error.hpp"
 - 
 - #if !defined(ASIO_NO_EXTENSIONS)
 - # include "asio/basic_streambuf_fwd.hpp"
 - #endif // !defined(ASIO_NO_EXTENSIONS)
 - 
 - #include "asio/detail/push_options.hpp"
 - 
 - namespace asio {
 - 
 - /**
 -  * @defgroup write_at asio::write_at
 -  *
 -  * @brief The @c write_at function is a composed operation that writes a
 -  * certain amount of data at a specified offset before returning.
 -  */
 - /*@{*/
 - 
 - /// Write all of the supplied data at the specified offset before returning.
 - /**
 -  * This function is used to write a certain number of bytes of data to a random
 -  * access device at a specified offset. The call will block until one of the
 -  * following conditions is true:
 -  *
 -  * @li All of the data in the supplied buffers has been written. That is, the
 -  * bytes transferred is equal to the sum of the buffer sizes.
 -  *
 -  * @li An error occurred.
 -  *
 -  * This operation is implemented in terms of zero or more calls to the device's
 -  * write_some_at function.
 -  *
 -  * @param d The device to which the data is to be written. The type must support
 -  * the SyncRandomAccessWriteDevice concept.
 -  *
 -  * @param offset The offset at which the data will be written.
 -  *
 -  * @param buffers One or more buffers containing the data to be written. The sum
 -  * of the buffer sizes indicates the maximum number of bytes to write to the
 -  * device.
 -  *
 -  * @returns The number of bytes transferred.
 -  *
 -  * @throws asio::system_error Thrown on failure.
 -  *
 -  * @par Example
 -  * To write a single data buffer use the @ref buffer function as follows:
 -  * @code asio::write_at(d, 42, asio::buffer(data, size)); @endcode
 -  * See the @ref buffer documentation for information on writing multiple
 -  * buffers in one go, and how to use it with arrays, boost::array or
 -  * std::vector.
 -  *
 -  * @note This overload is equivalent to calling:
 -  * @code asio::write_at(
 -  *     d, offset, buffers,
 -  *     asio::transfer_all()); @endcode
 -  */
 - template <typename SyncRandomAccessWriteDevice, typename ConstBufferSequence>
 - std::size_t write_at(SyncRandomAccessWriteDevice& d,
 -     uint64_t offset, const ConstBufferSequence& buffers);
 - 
 - /// Write all of the supplied data at the specified offset before returning.
 - /**
 -  * This function is used to write a certain number of bytes of data to a random
 -  * access device at a specified offset. The call will block until one of the
 -  * following conditions is true:
 -  *
 -  * @li All of the data in the supplied buffers has been written. That is, the
 -  * bytes transferred is equal to the sum of the buffer sizes.
 -  *
 -  * @li An error occurred.
 -  *
 -  * This operation is implemented in terms of zero or more calls to the device's
 -  * write_some_at function.
 -  *
 -  * @param d The device to which the data is to be written. The type must support
 -  * the SyncRandomAccessWriteDevice concept.
 -  *
 -  * @param offset The offset at which the data will be written.
 -  *
 -  * @param buffers One or more buffers containing the data to be written. The sum
 -  * of the buffer sizes indicates the maximum number of bytes to write to the
 -  * device.
 -  *
 -  * @param ec Set to indicate what error occurred, if any.
 -  *
 -  * @returns The number of bytes transferred.
 -  *
 -  * @par Example
 -  * To write a single data buffer use the @ref buffer function as follows:
 -  * @code asio::write_at(d, 42,
 -  *     asio::buffer(data, size), ec); @endcode
 -  * See the @ref buffer documentation for information on writing multiple
 -  * buffers in one go, and how to use it with arrays, boost::array or
 -  * std::vector.
 -  *
 -  * @note This overload is equivalent to calling:
 -  * @code asio::write_at(
 -  *     d, offset, buffers,
 -  *     asio::transfer_all(), ec); @endcode
 -  */
 - template <typename SyncRandomAccessWriteDevice, typename ConstBufferSequence>
 - std::size_t write_at(SyncRandomAccessWriteDevice& d,
 -     uint64_t offset, const ConstBufferSequence& buffers,
 -     asio::error_code& ec);
 - 
 - /// Write a certain amount of data at a specified offset before returning.
 - /**
 -  * This function is used to write a certain number of bytes of data to a random
 -  * access device at a specified offset. The call will block until one of the
 -  * following conditions is true:
 -  *
 -  * @li All of the data in the supplied buffers has been written. That is, the
 -  * bytes transferred is equal to the sum of the buffer sizes.
 -  *
 -  * @li The completion_condition function object returns 0.
 -  *
 -  * This operation is implemented in terms of zero or more calls to the device's
 -  * write_some_at function.
 -  *
 -  * @param d The device to which the data is to be written. The type must support
 -  * the SyncRandomAccessWriteDevice concept.
 -  *
 -  * @param offset The offset at which the data will be written.
 -  *
 -  * @param buffers One or more buffers containing the data to be written. The sum
 -  * of the buffer sizes indicates the maximum number of bytes to write to the
 -  * device.
 -  *
 -  * @param completion_condition The function object to be called to determine
 -  * whether the write operation is complete. The signature of the function object
 -  * must be:
 -  * @code std::size_t completion_condition(
 -  *   // Result of latest write_some_at operation.
 -  *   const asio::error_code& error,
 -  *
 -  *   // Number of bytes transferred so far.
 -  *   std::size_t bytes_transferred
 -  * ); @endcode
 -  * A return value of 0 indicates that the write operation is complete. A
 -  * non-zero return value indicates the maximum number of bytes to be written on
 -  * the next call to the device's write_some_at function.
 -  *
 -  * @returns The number of bytes transferred.
 -  *
 -  * @throws asio::system_error Thrown on failure.
 -  *
 -  * @par Example
 -  * To write a single data buffer use the @ref buffer function as follows:
 -  * @code asio::write_at(d, 42, asio::buffer(data, size),
 -  *     asio::transfer_at_least(32)); @endcode
 -  * See the @ref buffer documentation for information on writing multiple
 -  * buffers in one go, and how to use it with arrays, boost::array or
 -  * std::vector.
 -  */
 - template <typename SyncRandomAccessWriteDevice, typename ConstBufferSequence,
 -     typename CompletionCondition>
 - std::size_t write_at(SyncRandomAccessWriteDevice& d,
 -     uint64_t offset, const ConstBufferSequence& buffers,
 -     CompletionCondition completion_condition);
 - 
 - /// Write a certain amount of data at a specified offset before returning.
 - /**
 -  * This function is used to write a certain number of bytes of data to a random
 -  * access device at a specified offset. The call will block until one of the
 -  * following conditions is true:
 -  *
 -  * @li All of the data in the supplied buffers has been written. That is, the
 -  * bytes transferred is equal to the sum of the buffer sizes.
 -  *
 -  * @li The completion_condition function object returns 0.
 -  *
 -  * This operation is implemented in terms of zero or more calls to the device's
 -  * write_some_at function.
 -  *
 -  * @param d The device to which the data is to be written. The type must support
 -  * the SyncRandomAccessWriteDevice concept.
 -  *
 -  * @param offset The offset at which the data will be written.
 -  *
 -  * @param buffers One or more buffers containing the data to be written. The sum
 -  * of the buffer sizes indicates the maximum number of bytes to write to the
 -  * device.
 -  *
 -  * @param completion_condition The function object to be called to determine
 -  * whether the write operation is complete. The signature of the function object
 -  * must be:
 -  * @code std::size_t completion_condition(
 -  *   // Result of latest write_some_at operation.
 -  *   const asio::error_code& error,
 -  *
 -  *   // Number of bytes transferred so far.
 -  *   std::size_t bytes_transferred
 -  * ); @endcode
 -  * A return value of 0 indicates that the write operation is complete. A
 -  * non-zero return value indicates the maximum number of bytes to be written on
 -  * the next call to the device's write_some_at function.
 -  *
 -  * @param ec Set to indicate what error occurred, if any.
 -  *
 -  * @returns The number of bytes written. If an error occurs, returns the total
 -  * number of bytes successfully transferred prior to the error.
 -  */
 - template <typename SyncRandomAccessWriteDevice, typename ConstBufferSequence,
 -     typename CompletionCondition>
 - std::size_t write_at(SyncRandomAccessWriteDevice& d,
 -     uint64_t offset, const ConstBufferSequence& buffers,
 -     CompletionCondition completion_condition, asio::error_code& ec);
 - 
 - #if !defined(ASIO_NO_EXTENSIONS)
 - #if !defined(ASIO_NO_IOSTREAM)
 - 
 - /// Write all of the supplied data at the specified offset before returning.
 - /**
 -  * This function is used to write a certain number of bytes of data to a random
 -  * access device at a specified offset. The call will block until one of the
 -  * following conditions is true:
 -  *
 -  * @li All of the data in the supplied basic_streambuf has been written.
 -  *
 -  * @li An error occurred.
 -  *
 -  * This operation is implemented in terms of zero or more calls to the device's
 -  * write_some_at function.
 -  *
 -  * @param d The device to which the data is to be written. The type must support
 -  * the SyncRandomAccessWriteDevice concept.
 -  *
 -  * @param offset The offset at which the data will be written.
 -  *
 -  * @param b The basic_streambuf object from which data will be written.
 -  *
 -  * @returns The number of bytes transferred.
 -  *
 -  * @throws asio::system_error Thrown on failure.
 -  *
 -  * @note This overload is equivalent to calling:
 -  * @code asio::write_at(
 -  *     d, 42, b,
 -  *     asio::transfer_all()); @endcode
 -  */
 - template <typename SyncRandomAccessWriteDevice, typename Allocator>
 - std::size_t write_at(SyncRandomAccessWriteDevice& d,
 -     uint64_t offset, basic_streambuf<Allocator>& b);
 - 
 - /// Write all of the supplied data at the specified offset before returning.
 - /**
 -  * This function is used to write a certain number of bytes of data to a random
 -  * access device at a specified offset. The call will block until one of the
 -  * following conditions is true:
 -  *
 -  * @li All of the data in the supplied basic_streambuf has been written.
 -  *
 -  * @li An error occurred.
 -  *
 -  * This operation is implemented in terms of zero or more calls to the device's
 -  * write_some_at function.
 -  *
 -  * @param d The device to which the data is to be written. The type must support
 -  * the SyncRandomAccessWriteDevice concept.
 -  *
 -  * @param offset The offset at which the data will be written.
 -  *
 -  * @param b The basic_streambuf object from which data will be written.
 -  *
 -  * @param ec Set to indicate what error occurred, if any.
 -  *
 -  * @returns The number of bytes transferred.
 -  *
 -  * @note This overload is equivalent to calling:
 -  * @code asio::write_at(
 -  *     d, 42, b,
 -  *     asio::transfer_all(), ec); @endcode
 -  */
 - template <typename SyncRandomAccessWriteDevice, typename Allocator>
 - std::size_t write_at(SyncRandomAccessWriteDevice& d,
 -     uint64_t offset, basic_streambuf<Allocator>& b,
 -     asio::error_code& ec);
 - 
 - /// Write a certain amount of data at a specified offset before returning.
 - /**
 -  * This function is used to write a certain number of bytes of data to a random
 -  * access device at a specified offset. The call will block until one of the
 -  * following conditions is true:
 -  *
 -  * @li All of the data in the supplied basic_streambuf has been written.
 -  *
 -  * @li The completion_condition function object returns 0.
 -  *
 -  * This operation is implemented in terms of zero or more calls to the device's
 -  * write_some_at function.
 -  *
 -  * @param d The device to which the data is to be written. The type must support
 -  * the SyncRandomAccessWriteDevice concept.
 -  *
 -  * @param offset The offset at which the data will be written.
 -  *
 -  * @param b The basic_streambuf object from which data will be written.
 -  *
 -  * @param completion_condition The function object to be called to determine
 -  * whether the write operation is complete. The signature of the function object
 -  * must be:
 -  * @code std::size_t completion_condition(
 -  *   // Result of latest write_some_at operation.
 -  *   const asio::error_code& error,
 -  *
 -  *   // Number of bytes transferred so far.
 -  *   std::size_t bytes_transferred
 -  * ); @endcode
 -  * A return value of 0 indicates that the write operation is complete. A
 -  * non-zero return value indicates the maximum number of bytes to be written on
 -  * the next call to the device's write_some_at function.
 -  *
 -  * @returns The number of bytes transferred.
 -  *
 -  * @throws asio::system_error Thrown on failure.
 -  */
 - template <typename SyncRandomAccessWriteDevice, typename Allocator,
 -     typename CompletionCondition>
 - std::size_t write_at(SyncRandomAccessWriteDevice& d, uint64_t offset,
 -     basic_streambuf<Allocator>& b, CompletionCondition completion_condition);
 - 
 - /// Write a certain amount of data at a specified offset before returning.
 - /**
 -  * This function is used to write a certain number of bytes of data to a random
 -  * access device at a specified offset. The call will block until one of the
 -  * following conditions is true:
 -  *
 -  * @li All of the data in the supplied basic_streambuf has been written.
 -  *
 -  * @li The completion_condition function object returns 0.
 -  *
 -  * This operation is implemented in terms of zero or more calls to the device's
 -  * write_some_at function.
 -  *
 -  * @param d The device to which the data is to be written. The type must support
 -  * the SyncRandomAccessWriteDevice concept.
 -  *
 -  * @param offset The offset at which the data will be written.
 -  *
 -  * @param b The basic_streambuf object from which data will be written.
 -  *
 -  * @param completion_condition The function object to be called to determine
 -  * whether the write operation is complete. The signature of the function object
 -  * must be:
 -  * @code std::size_t completion_condition(
 -  *   // Result of latest write_some_at operation.
 -  *   const asio::error_code& error,
 -  *
 -  *   // Number of bytes transferred so far.
 -  *   std::size_t bytes_transferred
 -  * ); @endcode
 -  * A return value of 0 indicates that the write operation is complete. A
 -  * non-zero return value indicates the maximum number of bytes to be written on
 -  * the next call to the device's write_some_at function.
 -  *
 -  * @param ec Set to indicate what error occurred, if any.
 -  *
 -  * @returns The number of bytes written. If an error occurs, returns the total
 -  * number of bytes successfully transferred prior to the error.
 -  */
 - template <typename SyncRandomAccessWriteDevice, typename Allocator,
 -     typename CompletionCondition>
 - std::size_t write_at(SyncRandomAccessWriteDevice& d, uint64_t offset,
 -     basic_streambuf<Allocator>& b, CompletionCondition completion_condition,
 -     asio::error_code& ec);
 - 
 - #endif // !defined(ASIO_NO_IOSTREAM)
 - #endif // !defined(ASIO_NO_EXTENSIONS)
 - 
 - /*@}*/
 - /**
 -  * @defgroup async_write_at asio::async_write_at
 -  *
 -  * @brief The @c async_write_at function is a composed asynchronous operation
 -  * that writes a certain amount of data at the specified offset before
 -  * completion.
 -  */
 - /*@{*/
 - 
 - /// Start an asynchronous operation to write all of the supplied data at the
 - /// specified offset.
 - /**
 -  * This function is used to asynchronously write a certain number of bytes of
 -  * data to a random access device at a specified offset. The function call
 -  * always returns immediately. The asynchronous operation will continue until
 -  * one of the following conditions is true:
 -  *
 -  * @li All of the data in the supplied buffers has been written. That is, the
 -  * bytes transferred is equal to the sum of the buffer sizes.
 -  *
 -  * @li An error occurred.
 -  *
 -  * This operation is implemented in terms of zero or more calls to the device's
 -  * async_write_some_at function, and is known as a <em>composed operation</em>.
 -  * The program must ensure that the device performs no <em>overlapping</em>
 -  * write operations (such as async_write_at, the device's async_write_some_at
 -  * function, or any other composed operations that perform writes) until this
 -  * operation completes. Operations are overlapping if the regions defined by
 -  * their offsets, and the numbers of bytes to write, intersect.
 -  *
 -  * @param d The device to which the data is to be written. The type must support
 -  * the AsyncRandomAccessWriteDevice concept.
 -  *
 -  * @param offset The offset at which the data will be written.
 -  *
 -  * @param buffers One or more buffers containing the data to be written.
 -  * Although the buffers object may be copied as necessary, ownership of the
 -  * underlying memory blocks is retained by the caller, which must guarantee
 -  * that they remain valid until the handler is called.
 -  *
 -  * @param handler The handler to be called when the write operation completes.
 -  * Copies will be made of the handler as required. The function signature of
 -  * the handler must be:
 -  * @code void handler(
 -  *   // Result of operation.
 -  *   const asio::error_code& error,
 -  *
 -  *   // Number of bytes written from the buffers. If an error
 -  *   // occurred, this will be less than the sum of the buffer sizes.
 -  *   std::size_t bytes_transferred
 -  * ); @endcode
 -  * Regardless of whether the asynchronous operation completes immediately or
 -  * not, the handler will not be invoked from within this function. On
 -  * immediate completion, invocation of the handler will be performed in a
 -  * manner equivalent to using asio::post().
 -  *
 -  * @par Example
 -  * To write a single data buffer use the @ref buffer function as follows:
 -  * @code
 -  * asio::async_write_at(d, 42, asio::buffer(data, size), handler);
 -  * @endcode
 -  * See the @ref buffer documentation for information on writing multiple
 -  * buffers in one go, and how to use it with arrays, boost::array or
 -  * std::vector.
 -  */
 - template <typename AsyncRandomAccessWriteDevice, typename ConstBufferSequence,
 -     typename WriteHandler>
 - ASIO_INITFN_RESULT_TYPE(WriteHandler,
 -     void (asio::error_code, std::size_t))
 - async_write_at(AsyncRandomAccessWriteDevice& d, uint64_t offset,
 -     const ConstBufferSequence& buffers,
 -     ASIO_MOVE_ARG(WriteHandler) handler);
 - 
 - /// Start an asynchronous operation to write a certain amount of data at the
 - /// specified offset.
 - /**
 -  * This function is used to asynchronously write a certain number of bytes of
 -  * data to a random access device at a specified offset. The function call
 -  * always returns immediately. The asynchronous operation will continue until
 -  * one of the following conditions is true:
 -  *
 -  * @li All of the data in the supplied buffers has been written. That is, the
 -  * bytes transferred is equal to the sum of the buffer sizes.
 -  *
 -  * @li The completion_condition function object returns 0.
 -  *
 -  * This operation is implemented in terms of zero or more calls to the device's
 -  * async_write_some_at function, and is known as a <em>composed operation</em>.
 -  * The program must ensure that the device performs no <em>overlapping</em>
 -  * write operations (such as async_write_at, the device's async_write_some_at
 -  * function, or any other composed operations that perform writes) until this
 -  * operation completes. Operations are overlapping if the regions defined by
 -  * their offsets, and the numbers of bytes to write, intersect.
 -  *
 -  * @param d The device to which the data is to be written. The type must support
 -  * the AsyncRandomAccessWriteDevice concept.
 -  *
 -  * @param offset The offset at which the data will be written.
 -  *
 -  * @param buffers One or more buffers containing the data to be written.
 -  * Although the buffers object may be copied as necessary, ownership of the
 -  * underlying memory blocks is retained by the caller, which must guarantee
 -  * that they remain valid until the handler is called.
 -  *
 -  * @param completion_condition The function object to be called to determine
 -  * whether the write operation is complete. The signature of the function object
 -  * must be:
 -  * @code std::size_t completion_condition(
 -  *   // Result of latest async_write_some_at operation.
 -  *   const asio::error_code& error,
 -  *
 -  *   // Number of bytes transferred so far.
 -  *   std::size_t bytes_transferred
 -  * ); @endcode
 -  * A return value of 0 indicates that the write operation is complete. A
 -  * non-zero return value indicates the maximum number of bytes to be written on
 -  * the next call to the device's async_write_some_at function.
 -  *
 -  * @param handler The handler to be called when the write operation completes.
 -  * Copies will be made of the handler as required. The function signature of the
 -  * handler must be:
 -  * @code void handler(
 -  *   // Result of operation.
 -  *   const asio::error_code& error,
 -  *
 -  *   // Number of bytes written from the buffers. If an error
 -  *   // occurred, this will be less than the sum of the buffer sizes.
 -  *   std::size_t bytes_transferred
 -  * ); @endcode
 -  * Regardless of whether the asynchronous operation completes immediately or
 -  * not, the handler will not be invoked from within this function. On
 -  * immediate completion, invocation of the handler will be performed in a
 -  * manner equivalent to using asio::post().
 -  *
 -  * @par Example
 -  * To write a single data buffer use the @ref buffer function as follows:
 -  * @code asio::async_write_at(d, 42,
 -  *     asio::buffer(data, size),
 -  *     asio::transfer_at_least(32),
 -  *     handler); @endcode
 -  * See the @ref buffer documentation for information on writing multiple
 -  * buffers in one go, and how to use it with arrays, boost::array or
 -  * std::vector.
 -  */
 - template <typename AsyncRandomAccessWriteDevice, typename ConstBufferSequence,
 -     typename CompletionCondition, typename WriteHandler>
 - ASIO_INITFN_RESULT_TYPE(WriteHandler,
 -     void (asio::error_code, std::size_t))
 - async_write_at(AsyncRandomAccessWriteDevice& d,
 -     uint64_t offset, const ConstBufferSequence& buffers,
 -     CompletionCondition completion_condition,
 -     ASIO_MOVE_ARG(WriteHandler) handler);
 - 
 - #if !defined(ASIO_NO_EXTENSIONS)
 - #if !defined(ASIO_NO_IOSTREAM)
 - 
 - /// Start an asynchronous operation to write all of the supplied data at the
 - /// specified offset.
 - /**
 -  * This function is used to asynchronously write a certain number of bytes of
 -  * data to a random access device at a specified offset. The function call
 -  * always returns immediately. The asynchronous operation will continue until
 -  * one of the following conditions is true:
 -  *
 -  * @li All of the data in the supplied basic_streambuf has been written.
 -  *
 -  * @li An error occurred.
 -  *
 -  * This operation is implemented in terms of zero or more calls to the device's
 -  * async_write_some_at function, and is known as a <em>composed operation</em>.
 -  * The program must ensure that the device performs no <em>overlapping</em>
 -  * write operations (such as async_write_at, the device's async_write_some_at
 -  * function, or any other composed operations that perform writes) until this
 -  * operation completes. Operations are overlapping if the regions defined by
 -  * their offsets, and the numbers of bytes to write, intersect.
 -  *
 -  * @param d The device to which the data is to be written. The type must support
 -  * the AsyncRandomAccessWriteDevice concept.
 -  *
 -  * @param offset The offset at which the data will be written.
 -  *
 -  * @param b A basic_streambuf object from which data will be written. Ownership
 -  * of the streambuf is retained by the caller, which must guarantee that it
 -  * remains valid until the handler is called.
 -  *
 -  * @param handler The handler to be called when the write operation completes.
 -  * Copies will be made of the handler as required. The function signature of the
 -  * handler must be:
 -  * @code void handler(
 -  *   // Result of operation.
 -  *   const asio::error_code& error,
 -  *
 -  *   // Number of bytes written from the buffers. If an error
 -  *   // occurred, this will be less than the sum of the buffer sizes.
 -  *   std::size_t bytes_transferred
 -  * ); @endcode
 -  * Regardless of whether the asynchronous operation completes immediately or
 -  * not, the handler will not be invoked from within this function. On
 -  * immediate completion, invocation of the handler will be performed in a
 -  * manner equivalent to using asio::post().
 -  */
 - template <typename AsyncRandomAccessWriteDevice, typename Allocator,
 -     typename WriteHandler>
 - ASIO_INITFN_RESULT_TYPE(WriteHandler,
 -     void (asio::error_code, std::size_t))
 - async_write_at(AsyncRandomAccessWriteDevice& d, uint64_t offset,
 -     basic_streambuf<Allocator>& b, ASIO_MOVE_ARG(WriteHandler) handler);
 - 
 - /// Start an asynchronous operation to write a certain amount of data at the
 - /// specified offset.
 - /**
 -  * This function is used to asynchronously write a certain number of bytes of
 -  * data to a random access device at a specified offset. The function call
 -  * always returns immediately. The asynchronous operation will continue until
 -  * one of the following conditions is true:
 -  *
 -  * @li All of the data in the supplied basic_streambuf has been written.
 -  *
 -  * @li The completion_condition function object returns 0.
 -  *
 -  * This operation is implemented in terms of zero or more calls to the device's
 -  * async_write_some_at function, and is known as a <em>composed operation</em>.
 -  * The program must ensure that the device performs no <em>overlapping</em>
 -  * write operations (such as async_write_at, the device's async_write_some_at
 -  * function, or any other composed operations that perform writes) until this
 -  * operation completes. Operations are overlapping if the regions defined by
 -  * their offsets, and the numbers of bytes to write, intersect.
 -  *
 -  * @param d The device to which the data is to be written. The type must support
 -  * the AsyncRandomAccessWriteDevice concept.
 -  *
 -  * @param offset The offset at which the data will be written.
 -  *
 -  * @param b A basic_streambuf object from which data will be written. Ownership
 -  * of the streambuf is retained by the caller, which must guarantee that it
 -  * remains valid until the handler is called.
 -  *
 -  * @param completion_condition The function object to be called to determine
 -  * whether the write operation is complete. The signature of the function object
 -  * must be:
 -  * @code std::size_t completion_condition(
 -  *   // Result of latest async_write_some_at operation.
 -  *   const asio::error_code& error,
 -  *
 -  *   // Number of bytes transferred so far.
 -  *   std::size_t bytes_transferred
 -  * ); @endcode
 -  * A return value of 0 indicates that the write operation is complete. A
 -  * non-zero return value indicates the maximum number of bytes to be written on
 -  * the next call to the device's async_write_some_at function.
 -  *
 -  * @param handler The handler to be called when the write operation completes.
 -  * Copies will be made of the handler as required. The function signature of the
 -  * handler must be:
 -  * @code void handler(
 -  *   // Result of operation.
 -  *   const asio::error_code& error,
 -  *
 -  *   // Number of bytes written from the buffers. If an error
 -  *   // occurred, this will be less than the sum of the buffer sizes.
 -  *   std::size_t bytes_transferred
 -  * ); @endcode
 -  * Regardless of whether the asynchronous operation completes immediately or
 -  * not, the handler will not be invoked from within this function. On
 -  * immediate completion, invocation of the handler will be performed in a
 -  * manner equivalent to using asio::post().
 -  */
 - template <typename AsyncRandomAccessWriteDevice, typename Allocator,
 -     typename CompletionCondition, typename WriteHandler>
 - ASIO_INITFN_RESULT_TYPE(WriteHandler,
 -     void (asio::error_code, std::size_t))
 - async_write_at(AsyncRandomAccessWriteDevice& d, uint64_t offset,
 -     basic_streambuf<Allocator>& b, CompletionCondition completion_condition,
 -     ASIO_MOVE_ARG(WriteHandler) handler);
 - 
 - #endif // !defined(ASIO_NO_IOSTREAM)
 - #endif // !defined(ASIO_NO_EXTENSIONS)
 - 
 - /*@}*/
 - 
 - } // namespace asio
 - 
 - #include "asio/detail/pop_options.hpp"
 - 
 - #include "asio/impl/write_at.hpp"
 - 
 - #endif // ASIO_WRITE_AT_HPP
 
 
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