How to get the exact message from recv() in winsoc

问题:

I'm developing a server-client application using Winsock in c++ and have a problem.

For getting the message from the client by the server I use the code below.

int result;
char buffer[200];

while (true)
{
    result = recv(client, buffer, 200, NULL);

    if (result > 0)
        cout << "\n\tMessage from client: \n\n\t" << message << ";";
}

I send the message "Hello" from the client to the server. However the buffer is actually this:

HelloÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌ

What am I missing?

回答1:

Since recv might not receive as many bytes as you told it, you typically use a function like this to receive specified number of bytes. Modified from here

int receiveall(int s, char *buf, int *len)
{
    int total = 0;        // how many bytes we've received
    int bytesleft = *len; // how many we have left to receive
    int n = -1;

    while(total < *len) {
        n = recv(s, buf+total, bytesleft, 0);
        if (n <= 0) { break; }
        total += n;
        bytesleft -= n;
    }

    *len = total; // return number actually received here

    return (n<=0)?-1:0; // return -1 on failure, 0 on success
} 

It's up to you to null terminate the string if you receive string which is not null terminated.

回答2:

The result tells you how many bytes were received. recv doesn't add a terminator since, in general, network data is binary data which might not be usable as a C-style string.

You can add a terminator yourself, if you know the message won't contain the termination character:

buffer[result] = 0;  // make sure the buffer is large enough

or make a string (or vector, or whatever) from it:

std::string message_str(message, result);

Note that what you receive might not be a single "message", especially if you're uses a stream protocol like TCP. It might contain more than one message, or just the start of one.

回答3:

memset(&receive[0], 0, sizeof(receive));
To clear the buffer

回答4:

You didn't initialize your buffer

char buffer[200] = {0};

while (true)
{
    result = recv(client, buffer, 200, NULL);

    if (result > 0)
        cout << "\n\tMessage from client: \n\n\t" << message << ";";
    memset(buffer, 0, 200);
}