inet_ntop — convert IPv4 and IPv6 addresses from binary to text form


#include <arpa/inet.h>

const char *inet_ntop(int af, const void *src,
                      char *dst, socklen_t size);


This function converts the network address structure src in the af address family into a character string. The resulting string is copied to the buffer pointed to by dst, which must be a non-null pointer. The caller specifies the number of bytes available in this buffer in the argument size.

inet_ntop() extends the inet_ntoa(3) function to support multiple address families, inet_ntoa(3) is now considered to be deprecated in favor of inet_ntop(). The following address families are currently supported:


src points to a struct in_addr (in network byte order) which is converted to an IPv4 network address in the dotted-decimal format, "ddd.ddd.ddd.ddd". The buffer dst must be at least INET_ADDRSTRLEN bytes long.


src points to a struct in6_addr (in network byte order) which is converted to a representation of this address in the most appropriate IPv6 network address format for this address. The buffer dst must be at least INET6_ADDRSTRLEN bytes long.

Return Value

On success, inet_ntop() returns a non-null pointer to dst. NULL is returned if there was an error, with errno set to indicate the error.



af was not a valid address family.


The converted address string would exceed the size given by size.


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

Interface Attribute Value
inet_ntop() Thread safety MT-Safe locale

Conforming to

POSIX.1-2001, POSIX.1-2008. Note that RFC 2553 defines a prototype where the last argument size is of type size_t. Many systems follow RFC 2553. Glibc 2.0 and 2.1 have size_t, but 2.2 and later have socklen_t.


AF_INET6 converts IPv4-mapped IPv6 addresses into an IPv6 format.


See inet_pton(3).

See Also

getnameinfo(3), inet(3), inet_pton(3)


This page is part of release 5.04 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

Referenced By

fmt_ip4(3), fmt_ip6(3), gethostbyname(3), getipnodebyname(3), getnameinfo(3), inet(3), inet_pton(3), lwres_net_ntop(3).

2017-09-15 Linux Programmer's Manual