如何在异步读取Boost Asio C ++上获取已传输的字节数

Question

As I've seen in Boost::asio the async read functions does not return the amount of bytes transferred but normal read functions does. How can I get the amount of bytes transferred when I use async_read_some? (Params: buffer, handler)

Answer 1

All forms of async_read expect a " ReadHandler " callback of the form

void handler(
  const boost::system::error_code& 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.
); 

The second parameter of your callback will be the number of bytes read.

Answer 2

The asynchronous read functions call a "handler" function (or function object) once the read is complete. The number of bytes transferred is passed to that function; the signature of the function must be:

void handler(
    const boost::system::error_code& error, // Result of operation.
    std::size_t bytes_transferred           // Number of bytes read.
);

The requirements for read handlers are documented here