Перед возвратом запишите определенное количество данных с заданным смещением.

template<
    typename SyncRandomAccessWriteDevice,
    typename ConstBufferSequence>
std::size_t write_at(
    SyncRandomAccessWriteDevice & d,
    uint64_t offset,
    const ConstBufferSequence & buffers);
  » more...
template<
    typename SyncRandomAccessWriteDevice,
    typename ConstBufferSequence>
std::size_t write_at(
    SyncRandomAccessWriteDevice & d,
    uint64_t offset,
    const ConstBufferSequence & buffers,
    boost::system::error_code & ec);
  » more...
template<
    typename SyncRandomAccessWriteDevice,
    typename ConstBufferSequence,
    typename CompletionCondition>
std::size_t write_at(
    SyncRandomAccessWriteDevice & d,
    uint64_t offset,
    const ConstBufferSequence & buffers,
    CompletionCondition completion_condition);
  » more...
template<
    typename SyncRandomAccessWriteDevice,
    typename ConstBufferSequence,
    typename CompletionCondition>
std::size_t write_at(
    SyncRandomAccessWriteDevice & d,
    uint64_t offset,
    const ConstBufferSequence & buffers,
    CompletionCondition completion_condition,
    boost::system::error_code & ec);
  » more...
template<
    typename SyncRandomAccessWriteDevice,
    typename Allocator>
std::size_t write_at(
    SyncRandomAccessWriteDevice & d,
    uint64_t offset,
    basic_streambuf< Allocator > & b);
  » more...
template<
    typename SyncRandomAccessWriteDevice,
    typename Allocator>
std::size_t write_at(
    SyncRandomAccessWriteDevice & d,
    uint64_t offset,
    basic_streambuf< Allocator > & b,
    boost::system::error_code & ec);
  » more...
template<
    typename SyncRandomAccessWriteDevice,
    typename Allocator,
    typename CompletionCondition>
std::size_t write_at(
    SyncRandomAccessWriteDevice & d,
    uint64_t offset,
    basic_streambuf< Allocator > & b,
    CompletionCondition completion_condition);
  » more...
template<
    typename SyncRandomAccessWriteDevice,
    typename Allocator,
    typename CompletionCondition>
std::size_t write_at(
    SyncRandomAccessWriteDevice & d,
    uint64_t offset,
    basic_streambuf< Allocator > & b,
    CompletionCondition completion_condition,
    boost::system::error_code & ec);
  » more...

Requirements

Заголовок:<boost/asio/write_at.hpp>

Заголовок удобства:<boost/asio.hpp>