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write_at (8 of 8 overloads)

Write a certain amount of data at a specified offset before returning.

    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);

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:

This operation is implemented in terms of zero or more calls to the device's write_some_at function.



The device to which the data is to be written. The type must support the SyncRandomAccessWriteDevice concept.


The offset at which the data will be written.


The basic_streambuf object from which data will be written.


The function object to be called to determine whether the write operation is complete. The signature of the function object must be:

std::size_t completion_condition(
  // Result of latest write_some_at operation.
  const boost::system::error_code& error,

  // Number of bytes transferred so far.
  std::size_t bytes_transferred

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.


Set to indicate what error occurred, if any.

Return Value

The number of bytes written. If an error occurs, returns the total number of bytes successfully transferred prior to the error.