为什么boost :: asio :: ip :: tcp :: iostream解析输入？

Question

I try to use the iostream class from boost ASIO to read binary data from a TCP socket. I use the standard extraction operator (operator>>) to read data from the stream. The environment I use is Visual Studio 2010. The problem is that when I read the stream it seems that the stream tries to parse the binary data as a string. At least this is what I have seens as I have debugged into the code.

Is there a way that I could use the iostream to read it as a binary stream and not as a string stream?

boost::asio::io_service dataServer;

boost::asio::ip::tcp::endpoint dataServerEndpoint(boost::asio::ip::tcp::v4(), dataServerPort);
boost::asio::ip::tcp::acceptor acceptor(dataServer, dataServerEndpoint);

boost::asio::ip::tcp::iostream dataServerStream;
acceptor.accept(*dataServerStream.rdbuf());

try
{
    vector<char> lineBuffer;

    while (!dataServerStream.eof())
    {

        bool eof = dataServerStream.eof();
        bool bad = dataServerStream.bad();
        bool fail = dataServerStream.fail();
        bool good = dataServerStream.good();

        uint64_t magic;
        dataServerStream >> magic;

So instead of just taking 8 bytes from stream and move it into the "magic" variable, it tries to parse the stream to get a valid stringified number. This of course fails and the fail bit will be set.

Answer 1

The input operator >> is expecting the input to be text, that is then converted to the correct data-type. As you can expect this will not work well with binary data.

You should be using read instead:

uint64_t magic;
dataServerStream.read(reinterpret_cast<char*>(&magic), sizeof(magic));

---

You also make a very common beginner mistake, in that you loop while (!eof) . This will not work as the eof flag is not set until after you try an input operation. This means you will iterate once to many.

Instead do eg

uint64_t magic;
while (dataServerStream.read(reinterpret_cast<char*>(&magic), sizeof(magic)))
{
    // Read the rest
}