何时在C中使用ntohs和ntohl？

这是我的工作代码来说明问题：

// Utility/Debugging method for dumping raw packet data
void dump(const unsigned char *data,int length) {
    unsigned int i;
    static unsigned long pcount = 0;

    // Decode Packet Header
    struct ether_header *eth_header = (struct ether_header *) data;

    printf("nn === PACKET %ld HEADER ===n",pcount);

    printf("nSource MAC: ");
    for (i = 0; i < 6; ++i) {
        printf("%02x",eth_header->ether_shost[i]);
        if (i < 5) {
            printf(":");
        }
    }

    printf("nDestination MAC: ");
    unsigned short ethernet_type = ntohs(eth_header->ether_type);
    printf("nType: %hun",ethernet_type); //Why not nthos?

    if (ethernet_type == ETHERTYPE_IP) { //IP Header
        printf("n == IP HEADER ==n");
        struct ip *ip_hdr = (struct ip*) (data + sizeof(struct ether_header));
        unsigned int size_ip = ip_hdr->ip_hl * 4; //why no nthos or nthol
        printf("nip_hdr->ip_hl: %u",ip_hdr->ip_hl); //why no nthos or nthol
        printf("nIP Version: %u",ip_hdr->ip_v); //why no nthos or nthol
        printf("nHeader Length: %u",ip_hdr->ip_hl); //why no nthos or nthol
        printf("nTotal Length: %hu",ntohs(ip_hdr->ip_len)); //?is this right?

        // TCP Header
        printf("n== TCP HEADER ==n");
        struct tcphdr *tcp_hdr = (struct tcphdr*) (data + sizeof(struct ether_header) + size_ip);
        unsigned int size_tcp = tcp_hdr->doff * 4; //why no nthos or nthol
        printf("n Source Port: %" PRIu16,ntohs(tcp_hdr->th_sport)); 
        printf("n Destination Port: %" PRIu16,ntohs(tcp_hdr->th_dport));
        printf("n fin: %" PRIu16,tcp_hdr->fin ); //As this is 1 bit,both nthos or nthol will work
        printf("n urg: %" PRIu16,tcp_hdr->urg ); //As this is 1 bit,both nthos or nthol will work
        printf("n ack_seq: %" PRIu32,ntohl(tcp_hdr->ack_seq));

        u_int16_t sourcePort = ntohs(tcp_hdr->th_sport);
        u_int16_t destinationPort = ntohs(tcp_hdr->th_sport);

        if (sourcePort == 80 || destinationPort == 80){
            printf("nnPORT 80!!!n");

            //Transport payload!
            printf("n  === TCP PAYLOAD DATA == n");

            // Decode Packet Data (Skipping over the header)
            unsigned int headers_size = ETH_HLEN + size_ip + size_tcp;
            unsigned int data_bytes = length - headers_size;
            const unsigned char *payload = data + headers_size;

            const static int output_sz = 500; // Output this many bytes at a time
            while (data_bytes > 0) {
                int output_bytes = data_bytes < output_sz ? data_bytes : output_sz;
                // Print data in raw hexadecimal form
                printf("| ");
                // Print data in ascii form
                for (i = 0; i < output_bytes; ++i) {
                    char byte = payload[i];
                    if ( (byte > 31 && byte < 127) || byte == 'n') {
                        // Byte is in printable ascii range
                        printf("%c",byte);  //why no nthos or nthol
                    } else {
                        printf(".");
                    }
                }
                payload += output_bytes;
                data_bytes -= output_bytes;
            }
        }

    }

    pcount++;
}

正如你所看到的,我有时会使用ntohs / ntohl,有时我也不使用ntohs / ntohl.我不明白何时使用哪个.