When and how to use C++ htonl function

Question

cout << "Hello World !" << endl;

For my very first post on stackoverflow: When are we supposed to use the htonl function? I have gone through the man page. However, I don't really understand when and how to use it.

Gironde

Whenever you are sending a 4 byte value to a different machine. The receiving machine then uses ntohl to recover the value. – Huey

You need it only if you are doing network programming or sharing binary data between different computer architectures. There's the corollary function ntohl, which is actually the same function as htonl on the same platform.. There's also htons and ntohs for 2-byte values. – Homemaker

It is worth mentioning, many modern applications transmit data textually, such as with XML over HTTP. But, lower level programming will deliver data in binary, and the world of computing is still heterogeneous. – Huey

Thank you for all the useful information ! – Gironde

Answer 1

Host TO Network translation. It makes sure the endian of a 32 bit data value is correct (Big endian) for network transport. ntohl -- Network TO Host -- is used by the receiver to ensure that the endian is correct for the receiver's CPU. Keep an eye out for htons and ntohs for handling 16 bits, and out there somewhere are likely htonll and ntohll for 64 bits.

Using all of them is as simple as pass in the number you want converted and out comes the converted number. You may find that absolutely nothing has happened on some processors because their endian is already big.

uint32_t inval = 0xAABBCCDD;
uint32_t outval = htonl(inval);

Will, on most desktop hardware, result in outval being set to 0xDDCCBBAA

Jessen