inet.h File Reference

  struct in_addr or some other internal binary representation, in network byte order).
 It returns 1 if the address was valid for the specified address family, or
 0 if the address was not parseable in the specified address family, or -1
 if some system error occurred.
 This function is presently valid for AF_INET and AF_INET6.

  struct in_addr or some other binary form, in network byte order) to presentation format
 (suitable for external display purposes).
 The size argument specifies the size, in bytes, of the buffer *dst It returns NULL if a system error occurs (in which case, errno will have been set), or it returns a pointer to the destination string.
 This function is presently valid for AF_INET and AF_INET6.

  The routines inet_addr and inet_aton interpret character strings representing
numbers expressed in the Internet standard . notation.

Examples:

#include <stdio.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#define IPV6ADDRSIZE 48
int main()
    {
     unsigned int nbo_value;
     char *ipaddrstring="1.2.3.4";
     char *ipaddrholdr=NULL;
     char *ipv6addrstring="8000::123:4567:89AB:CDEF";
     struct in_addr ipstruct;
     struct in6_addr ipv6struct;
     char result[IPV6ADDRSIZE];
     int err;
     int size;
     const char* error;
     nbo_value=inet_addr(ipaddrstring);
     if(nbo_value == -1)
      {
       printf("inet_addr failed0);
      }
     else
      {
       printf("inet_addr passed0);
      }
     ipstruct.s_addr=nbo_value;
     ipaddrholdr=inet_ntoa(ipstruct);
     if(ipaddrholdr==NULL)
      {
       printf("inet_ntoa failed0);
      }
     else
      {
      printf("ipaddr is %s0,ipaddrholdr);
      }
     err=inet_pton(AF_INET6,ipv6addrstring ,&ipv6struct;);
     if(err ==0  || err==-1)
     printf("inet_pton Failed0);
     else
     printf("inet_pton passed0);
     size=sizeof(result);
     error=inet_ntop(AF_INET6,&ipv6struct.s6;_addr,result,size);     
     if(error==NULL)
      {
      printf("inet_ntop failed");
      }
     else
      {
      printf("inet_ntop passed");
      }
     err=inet_aton(ipaddrstring,&ipstruct;);
     if(err==0)
     {
      printf("invalid address ");
     }
     else
      {
      printf("inet_aton passed ");
      }
    
     return 0;
}
Output:
inet_addr passed
ipaddr is 1.2.3.4
inet_pton passed
inet_ntop passed
inet_aton passed

The inet_ntop and inet_pton functions conform to -xns5.2. Note that inet_pton does not accept 1-, 2-, or 3-part dotted addresses; all four parts must be specified and are interpreted only as decimal values. This is a narrower input set than that accepted by inet_aton. These functions appeared in BSD 4.2.