Interpretting payload using libpcap

So I've been playing around with libpcap lately, and I have a quick question. Here's the code in question:

while( (result = pcap_next_ex(adapterHandle, &header, &packetData)) >= 0)
{
    if(result == 0) // Packet was dropped
        continue;


    ethernet = (struct sniff_ethernet*)packetData;
    ip = (struct sniff_ip*)(packetData + SIZE_ETHERNET);
    size_ip = IP_HL(ip)*4;
    ip_len = ntohs(ip->ip_len);

    if(ip->ip_p != IPPROTO_TCP)
        continue;

    tcp = (struct sniff_tcp*)(packetData + SIZE_ETHERNET + size_ip);
    size_tcp = TH_OFF(tcp)*4;
    if(size_tcp < 20)
    {
        cout << "Invalid TCP Header" << endl;
        exit(-1);
    }

    payload = (u_char*)(packetData + SIZE_ETHERNET + size_ip + size_tcp);
    size_payload = ip_len - (size_ip + size_tcp);

    cout << "************** Output A ******************" << endl;
    开发者_如何学Pythoncout << payload << endl;
    cout << "*************** Output B *****************" << endl;
    for(int i=0; i<size_payload; i++)
        cout << payload[i];
}

So in my test I set it up so that I only capture HTTP "GET" requests. Now in my mind the output of Output A and Output B should be the same, printing only the HTTP header. Output B always prints it out correctly, but Output A occasionally has the HTTP header plus about 7 bytes of random text added on to it as well(Like this "ï╤↔N↓ƒ♂").

So the questions are where does that garbled text come from? And what's the difference between just printing the payload directly as in Output A vs looping through it and printing each character as in Output B?

Well, if it's not NUL-terminated (\0) it won't know where to stop, so it will print garbage text. You might want to do:

payload[size_payload] = '\0'; /* Before using it. */