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Function gethostbyaddr

Function gethostbyaddr performs a DNS lookup on a given IP address:

struct hostent * gethostbyaddr(char * address, int len, int type);

Parameters

address

32-bit IP address in network byte order.

len

Length of *address. Must be 4.

type

Type of address. Must be AF_INET.

return value

Returns pointer to a hostent structure if successful, otherwise NULL. If an error occurred, call xn_getlasterror and xn_geterror_string to return the error value. Possible values for this function are:

This function performs the reverse of gethostbyname, taking a 32-bit IP address and returning a pointer to a hostent structure, in which the domain name string is contained. The returned pointer points to an entry in an internal host cache. The entries are allocated using a round robin method; therefore, the information returned should be extracted immediately from the entry returned. DNS uses the UDP protocol to retrieve the information from the DNS server.

Note that xn_set_server_list must have been called before this function can be used.

The hostentext structure is defined as follows:

struct hostent 
{ 
    char *         h_name;             /* official name of host */  
    char *         h_aliases[1];       /* alias list */  
    WORD           h_addrtype;         /* host address type */  
    WORD           h_len               /* length of address */  
    char *         h_addrlist[3]       /* list of addresses */  
    long           l_time_to_live;     /* Time to live for entry */  
    int            b_used;             /* 1 if entry is used */  
    char           sz_name[100]; 
    struct in_addr ip_addr; 
    char           alias[100]; 
};

Socket API

Function connect

Function gethostbyname