Boost asio＆ssl＆错误代码

Question

Considering this code:

const std::size_t rawBufferSize = 1024;
char rawBuffer[rawBufferSize] = { 0 };
boost::asio::ssl::stream< boost::asio::ip::tcp::socket >* sslStream;

... // initializing stuff

boost::system::error_code ec;
auto buffer = boost::asio::buffer(rawBuffer, rawBufferSize);

for(; ; )
{
   int readBytes = sslStream->read_some(buffer, ec); // I know that read_some return std::size_t (unsigned int)...

   // here, readBytes equals -1

   if (ec)
       break;

   ... (1)
}

How is it possible that "readBytes" equals -1 and the line "(1)" is reached.

Any clue of what I am doing wrong?

Answer 1

In error_code.hpp you can find this definition:

class error_code
{
    ...

    typedef void (*unspecified_bool_type)();
    static void unspecified_bool_true() {}

    operator unspecified_bool_type() const  // true if error
    { 
      return m_val == 0 ? 0 : unspecified_bool_true;
    }

    bool operator!() const  // true if no error
    {
      return m_val == 0;
    }
    ...
}

If you use something like this:

if (!ec) {
    // no error
}

you get correct behavior, I hope it's clear. When you call this:

if (ec) {
    // error
}

you in fact call operator unspecified_bool_type() , because it returns a pointer (to function) and that can be converted to bool. If there is an error, it returns pointer to unspecified_bool_true which is not null. Therefore it works correctly and it won't solve the problem.

Answer 2

In your case, your error_code variable is not a pointer, so the following if statement

if (ec)
   break;

does NOT check correctly if an error_code actually exists.

You need to do this to check as to whether an error_code exists:

if (ec.value() != 0) break;

Now, when an error has occurred, it will break correctly.

The value of the error_code, can be any of these error conditions, inside the enum .