htonl, htons, ntohl, ntohs — convert values between host and network byte order


#include <arpa/inet.h>
uint32_t htonl( uint32_t hostlong);
uint16_t htons( uint16_t hostshort);
uint32_t ntohl( uint32_t netlong);
uint16_t ntohs( uint16_t netshort);


The htonl() function converts the unsigned integer hostlong from host byte order to network byte order.

The htons() function converts the unsigned short integer hostshort from host byte order to network byte order.

The ntohl() function converts the unsigned integer netlong from network byte order to host byte order.

The ntohs() function converts the unsigned short integer netshort from network byte order to host byte order.

On the i386 the host byte order is Least Significant Byte first, whereas the network byte order, as used on the Internet, is Most Significant Byte first.


For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
htonl(), htons(), ntohl(), ntohs() Thread safety MT-Safe


POSIX.1-2001, POSIX.1-2008.

Some systems require the inclusion of <netinet/in.h> instead of <arpa/inet.h>


bswap(3), endian(3), gethostbyname(3), getservent(3)


This page is part of release 5.11 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at−pages/.

  Copyright 1993 David Metcalfe (

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References consulted:
    Linux libc source code
    Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
    386BSD man pages
Modified Sat Jul 24 21:29:05 1993 by Rik Faith (
Modified Thu Jul 26 14:06:20 2001 by Andries Brouwer (