#### read (5 of 6 overloads)

Attempt to read a certain amount of data from a stream before returning.

    template<
        typename SyncReadStream,
        typename Allocator,
        typename CompletionCondition>
    std::size_t read(
        SyncReadStream & s,
        basic_streambuf< Allocator > & b,
        CompletionCondition completion_condition);

This function is used to read a certain number of bytes of data from a stream. The call will block 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 read_some function.

###### Parameters

s

  The stream from which the data is to be read. The type must support the SyncReadStream concept.

b

  The basic_streambuf object into which the data will be read.

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 asio::error_code& 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 read_some function are required.

###### Return Value

The number of bytes transferred.

###### Exceptions

asio::system_error

  Thrown on failure.