我很困惑什么时候使用ntohs和ntohl。我知道你什么时候用unt16_t和ntohl uint32_t使用ntohs。但那些unsigned int或那些指定了特定位数的函数(例如u_int16_t doff：4;)呢？什么时候在C中使用ntohs和ntohl？

这是我工作的代码在于向世人证明问题：

// 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("\n\n === 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: %hu\n", 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("\n\nPORT 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++;

}

正如你可以看到有次我用ntohs和/和再用ntohl有次我都不使用。我不明白何时使用哪个。