Estou criando um soquete UDP (AF_INET, SOCK_DGRAM, IPPROTO_UDP) via Winsock e tentandorecvfrom neste soquete, mas sempre retorna -1 e eu recebo WSAEINVAL (10022). Por quê?

Quando eubind() a porta, isso não acontece, mas eu li que é muito ruim ligar o soquete do cliente.

Estou enviando dados para o meu servidor, o que responde, ou pelo menos, tenta.

Inc::STATS CConnection::_RecvData(sockaddr* addr, std::string &strData)
{
    int ret;            // return code
    int len;            // length of the data
    int fromlen;        // sizeof(sockaddr)
    char *buffer;       // will hold the data
    char c;

    //recv length of the message
    fromlen = sizeof(sockaddr);
    ret = recvfrom(m_InSock, &c, 1, 0, addr, &fromlen);
    if(ret != 1)
    {
#ifdef __MYDEBUG__
        std::stringstream ss;
        ss << WSAGetLastError();
        MessageBox(NULL, ss.str().c_str(), "", MB_ICONERROR | MB_OK);
#endif
        return Inc::ERECV;
    }
    ...

Este é um exemplo prático que escrevi alguns momentos atrás e funciona sem a necessidade de chamarbind() no cliente:

#pragma comment(lib, "Ws2_32.lib")

#define WIN32_LEAN_AND_MEAN

#include <WS2tcpip.h>
#include <Windows.h>
#include <iostream>

using namespace std;

int main()
{
    SOCKET sock;
    addrinfo* pAddr;
    addrinfo hints;
    sockaddr sAddr;
    int fromlen;
    const char czPort[] = "12345";
    const char czAddy[] = "some ip";

    WSADATA wsa;
    unsigned short usWSAVersion = MAKEWORD(2,2);

    char Buffer[22] = "TESTTESTTESTTESTTEST5";
    int ret;

    //Start WSA
    WSAStartup(usWSAVersion, &wsa);

    //Create Socket
    sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);

    //Resolve host address
    memset(&hints, 0, sizeof(hints));
    hints.ai_family = AF_INET;
    hints.ai_protocol = IPPROTO_UDP;
    hints.ai_socktype = SOCK_DGRAM;

    if(getaddrinfo(czAddy, czPort, &hints, &pAddr))
    {
        std::cerr << "Could not resolve address...\n";
        std::cin.get();
        return 1;
    }

    //Start Transmission
    while(1)
    {
        ret = sendto(sock, Buffer, sizeof(Buffer), 0, pAddr->ai_addr,
                     pAddr->ai_addrlen);
        if(ret != sizeof(Buffer))
        {
            std::cerr << "Could not send data\n";
            std::cin.get();
            return 1;
        }

        fromlen = sizeof(SOCKADDR);
        ret = recvfrom(sock, Buffer, sizeof(Buffer), 0, &sAddr, &fromlen);
        if(ret != sizeof(Buffer))
        {
            std::cout << "Could not receive data -  error: " << 
                          WSAGetLastError() << std::endl;
            std::cin.get();
            return 1;
        }

        Buffer[ret-1] = '\0';
        std::cout << "Received: " << Buffer << std::endl;
    }
    return 0;
}