C++ UDP recvfrom is acting strange, WSAGetLastError = 10014

Question

My code is behaving very strange on Windows, but working on Linux... This is my server.cpp:

#include <cstdio>
#include "packet.h"
#include "socket.h"

int main(int argc, char *argv[])
{
Socket s;

s.bindAt(1337);
for (int i = 0; i < 20; i++) {
    Packet p;
    int32_t a;
    char *b;

    int abc = s.receive();
    printf("abc = %d\n", abc);
    printf("error = %d\n", WSAGetLastError());
    p.getInt(&a);
    p.getString(&b);

    printf("int = %d\nstring = %s\n", a, b);
    delete[] b;
}

return 0;
}

and here is the socket.cpp:

Socket::Socket()
{
#ifdef _WIN32
WSADATA wsa;
if (sockNum == 0 && WSAStartup(MAKEWORD(2, 2), &wsa) != 0)
    throw 1;
#endif

sock = socket(AF_INET, SOCK_DGRAM, 0);
#ifdef _WIN32
if (sock == INVALID_SOCKET)
#else
if (sock == -1)
#endif
    throw 2;

addrlen = 0;
sockNum++;
}


int Socket::bindAt(unsigned short port)
{
struct sockaddr_in sa = { 0 };
memset(&sa, 0, sizeof(sa));

sa.sin_family = AF_INET;
sa.sin_port = htons(port);
sa.sin_addr.s_addr = htonl(INADDR_ANY);
return bind(sock, (struct sockaddr *) &sa, sizeof(sa));
}

ssize_t Socket::receive()
{
ssize_t n;

#ifdef _WIN32

char msg[100];
n = recvfrom(sock,msg, sizeof(msg), 0,(SOCKADDR*) &addr, &addrlen);
#else
n = recvfrom(sock, p->buf, p->bufSize, 0,
        (struct sockaddr *) &addr, &addrlen);
#endif
/*if (n < 0)
    p->bufSize = 0;
else
    p->bufSize = n;*/
return n;
}

and basically the header of it:

typedef SOCKET socket_t;
typedef int ssize_t;

class Socket
{
public:
socket_t sock;
socklen_t addrlen;
struct sockaddr_in addr;

Socket();
~Socket();

int connect(const char *ip, unsigned short port);
int bindAt(unsigned short port);
ssize_t send(Packet *p);
ssize_t receive();
};

If I change the last 2 parameters of the recvfrom, the (SOCKADDR*) &addr, and &addrlen to NULL it works, but what is wrong with these 2 parameters?

Answer 1

instead of this :

addrlen = 0;

do this:

addrlen = sizeof(sockaddr_in)

it should work, because you are identifying correctly the size of the output address buffer pointer.

Answer 2

From MSDN description of WSAEFAULT (10014):

The system detected an invalid pointer address in attempting to use a pointer argument of a call. This error occurs if an application passes an invalid pointer value, or if the length of the buffer is too small . For instance, if the length of an argument, which is a sockaddr structure, is smaller than the sizeof(sockaddr).

So if you supply an uninitialized value of addrlen , it may be too small, and result in this error.

If addr is NULL , it means you don't want the address filled in, so addrlen is ignored.