Question

I try to send a structure from a client to a server. I read in the internet that i have to type cast the structure to a char array, but when i try this the char has not content.

Here is my struct:

struct packet
{
    int pa_ID;
    char message[MESSAGESIZE];
};

And here I try to send the struct:

int sendFile(FILE *file, SOCKET sock)
{
int amountToSend, amountSent;
int i = 0;
char buffer[BUFFERSIZE], serializedPacket[BUFFERSIZE];

while (!feof(file)) {
    struct packet p;
    fgets(p.message, MESSAGESIZE, file);
    p.pa_ID = i;

    if (p.message[strlen(p.message) - 1] == '\n')
        p.message[strlen(p.message) - 1] = '\0';

    amountToSend = sprintf_s(serializedPacket, sizeof(buffer), (char*)&p);
    amountSent = send(sock, serializedPacket, amountToSend, 0);
    if (amountSent == SOCKET_ERROR) {
        fprintf(stderr, "send() failed with error %d\n", WSAGetLastError());
        getchar();
        WSACleanup();
        return -1;
    }
    printf("Send %d bytes (out of %d bytes) of data: [%.*s]\n", amountSent, amountToSend, amountToSend, serializedPacket);
    memset(buffer, 0, sizeof(buffer));
    memset(p.message, 0, sizeof(p.message));
    memset(&p, 0, sizeof(p));
    i++;
}

fclose(file);
return 0;

}

The reading from the file functions without errors, but the serializedPack is just empty and I really dont see why.
Hope someone can help.

Answer 1

This:

amountToSend = sprintf_s(serializedPacket, sizeof(buffer), (char*)&p);

doesn’t make any sense at all.

The third argument to sprintf_s() is a formatting string, but you pass a pointer to a structure, re-cast as a character pointer. This makes absolutely no sense.

Representing your structure as a textual string (serializing to string) might be a good idea, but then you need a proper formatting string:

amountToSend = sprintf_s(serializedPacket, sizeof(buffer), "%d %s", p.pa_ID, p.message);

Depending on how you send this, you might also want to include the 0-terminator for the string in the transmitted data.