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# boost::asio::async_read

## Functions

template<typename Async_Read_Stream, typename Mutable_Buffers, typename Handler>
void | boost::asio::async_read (Async_Read_Stream &s, const Mutable_Buffers &buffers, Handler handler)
| Start an asynchronous operation to read a certain amount of data from a stream.
template<typename Async_Read_Stream, typename Mutable_Buffers, typename Completion_Condition, typename Handler>
void | boost::asio::async_read (Async_Read_Stream &s, const Mutable_Buffers &buffers, Completion_Condition completion_condition, Handler handler)
| Start an asynchronous operation to read a certain amount of data from a stream.
template<typename Async_Read_Stream, typename Allocator, typename Handler>
void | boost::asio::async_read (Async_Read_Stream &s, basic_streambuf< Allocator > &b, Handler handler)
| Start an asynchronous operation to read a certain amount of data from a stream.
template<typename Async_Read_Stream, typename Allocator, typename Completion_Condition, typename Handler>
void | boost::asio::async_read (Async_Read_Stream &s, basic_streambuf< Allocator > &b, Completion_Condition completion_condition, Handler handler)
| Start an asynchronous operation to read a certain amount of data from a stream.

## Function Documentation

template<typename Async_Read_Stream, typename Mutable_Buffers, typename Handler>

void boost::asio::async_read | ( | Async_Read_Stream & | s,
|  | const Mutable_Buffers & | buffers,
|  | Handler | handler |
| ) |  |  |

Start an asynchronous operation to read a certain amount of data from a stream.

This function is used to asynchronously read a certain number of bytes of data from a stream. The function call always returns immediately. The asynchronous operation will continue until one of the following conditions is true:

- The supplied buffers are full. That is, the bytes transferred is equal to the sum of the buffer sizes.

- An error occurred.

This operation is implemented in terms of one or more calls to the stream's async_read_some function.

Parameters:

  | s | The stream from which the data is to be read. The type must support the Async_Read_Stream concept.
  | buffers | One or more buffers into which the data will be read. The sum of the buffer sizes indicates the maximum number of bytes to read from the stream. 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.

  handler

  The handler to be called when the read operation completes. Copies will be made of the handler as required. The function signature of the handler must be:

       void handler(
         const Async_Read_Stream::error_type& error, // Result of operation.

         std::size_t bytes_transferred               // Number of bytes copied into
                                                     // the buffers. If an error
                                                     // occurred, this will be the
                                                     // number of bytes successfully
                                                     // transferred prior to the
                                                     // error.
       );

  Regardless of whether the asynchronous operation completes immediately or not, the handler will not be invoked from within this function. Invocation of the handler will be performed in a manner equivalent to using boost::asio::io_service::post().

Example:
  To read into a single data buffer use the boost::asio::buffer function as follows:

       boost::asio::async_read(s, boost::asio::buffer(data, size), handler);

  See the boost::asio::buffer documentation for information on reading into multiple buffers in one go, and how to use it with arrays, boost::array or std::vector.

Note:
  This overload is equivalent to calling:

       boost::asio::async_read(
           s, buffers,
           boost::asio::transfer_all(),
           handler);

template<typename Async_Read_Stream, typename Mutable_Buffers, typename Completion_Condition, typename Handler>

void boost::asio::async_read | ( | Async_Read_Stream & | s,
|  | const Mutable_Buffers & | buffers,
|  | Completion_Condition | completion_condition,
|  | Handler | handler |
| ) |  |  |

Start an asynchronous operation to read a certain amount of data from a stream.

This function is used to asynchronously read a certain number of bytes of data from a stream. The function call always returns immediately. The asynchronous operation will continue until one of the following conditions is true:

- The supplied buffers are full. That is, the bytes transferred is equal to the sum of the buffer sizes.

- The completion_condition function object returns true.

Parameters:

  | s | The stream from which the data is to be read. The type must support the Async_Read_Stream concept.
  | buffers | One or more buffers into which the data will be read. The sum of the buffer sizes indicates the maximum number of bytes to read from the stream. 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.

  completion_condition

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

       bool completion_condition(
         const Async_Read_Stream::error_type& error, // Result of latest read_some
                                                     // operation.

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

  A return value of true indicates that the read operation is complete. False indicates that further calls to the stream's async_read_some function are required.

  handler

  The handler to be called when the read operation completes. Copies will be made of the handler as required. The function signature of the handler must be:

       void handler(
         const Async_Read_Stream::error_type& error, // Result of operation.

         std::size_t bytes_transferred               // Number of bytes copied into
                                                     // the buffers. If an error
                                                     // occurred, this will be the
                                                     // number of bytes successfully
                                                     // transferred prior to the
                                                     // error.
       );

  Regardless of whether the asynchronous operation completes immediately or not, the handler will not be invoked from within this function. Invocation of the handler will be performed in a manner equivalent to using boost::asio::io_service::post().

Example:
  To read into a single data buffer use the boost::asio::buffer function as follows:

       boost::asio::async_read(s,
           boost::asio::buffer(data, size),
           boost::asio::transfer_at_least(32),
           handler);

  See the boost::asio::buffer documentation for information on reading into multiple buffers in one go, and how to use it with arrays, boost::array or std::vector.

template<typename Async_Read_Stream, typename Allocator, typename Handler>

void boost::asio::async_read | ( | Async_Read_Stream & | s,
|  | basic_streambuf< Allocator > & | b,
|  | Handler | handler |
| ) |  |  |

Start an asynchronous operation to read a certain amount of data from a stream.

This function is used to asynchronously read a certain number of bytes of data from a stream. The function call always returns immediately. The asynchronous operation will continue until one of the following conditions is true:

- An error occurred.

Parameters:

  | s | The stream from which the data is to be read. The type must support the Async_Read_Stream concept.

This operation is implemented in terms of one or more calls to the stream's async_read_some function.

Parameters:

  | b | A basic_streambuf object into which the data will be read. Ownership of the streambuf is retained by the caller, which must guarantee that it remains valid until the handler is called.

  handler

  The handler to be called when the read operation completes. Copies will be made of the handler as required. The function signature of the handler must be:

       void handler(
         const Async_Read_Stream::error_type& error, // Result of operation.

         std::size_t bytes_transferred               // Number of bytes copied into
                                                     // the buffers. If an error
                                                     // occurred, this will be the
                                                     // number of bytes successfully
                                                     // transferred prior to the
                                                     // error.
       );

  Regardless of whether the asynchronous operation completes immediately or not, the handler will not be invoked from within this function. Invocation of the handler will be performed in a manner equivalent to using boost::asio::io_service::post().

Note:
  This overload is equivalent to calling:

       boost::asio::async_read(
           s, b,
           boost::asio::transfer_all(),
           handler);

template<typename Async_Read_Stream, typename Allocator, typename Completion_Condition, typename Handler>

void boost::asio::async_read | ( | Async_Read_Stream & | s,
|  | basic_streambuf< Allocator > & | b,
|  | Completion_Condition | completion_condition,
|  | Handler | handler |
| ) |  |  |

Start an asynchronous operation to read a certain amount of data from a stream.

This function is used to asynchronously read a certain number of bytes of data from a stream. The function call always returns immediately. The asynchronous operation will continue until one of the following conditions is true:

- The completion_condition function object returns true.

This operation is implemented in terms of one or more calls to the stream's async_read_some function.

Parameters:

  | s | The stream from which the data is to be read. The type must support the Async_Read_Stream concept.
  | b | A basic_streambuf object into which the data will be read. Ownership of the streambuf is retained by the caller, which must guarantee that it remains valid until the handler is called.

  completion_condition

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

       bool completion_condition(
         const Async_Read_Stream::error_type& error, // Result of latest read_some
                                                     // operation.

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

  A return value of true indicates that the read operation is complete. False indicates that further calls to the stream's async_read_some function are required.

  handler

  The handler to be called when the read operation completes. Copies will be made of the handler as required. The function signature of the handler must be:

       void handler(
         const Async_Read_Stream::error_type& error, // Result of operation.

         std::size_t bytes_transferred               // Number of bytes copied into
                                                     // the buffers. If an error
                                                     // occurred, this will be the
                                                     // number of bytes successfully
                                                     // transferred prior to the
                                                     // error.
       );

  Regardless of whether the asynchronous operation completes immediately or not, the handler will not be invoked from within this function. Invocation of the handler will be performed in a manner equivalent to using boost::asio::io_service::post().

| Copyright © 2003 - 2006 Christopher M. Kohlhoff