inet_aton,inet_addr和inet_ntoa在點分十進位制數串（如，“192.168.1.10")與他的32位網路位元組二進位制值之間轉換IPV4地址，有2個比較新的函式inet_pton和inet_ntop，這2個對IPV4和IPV6地址都能處理。

       char *inet_ntoa(struct in_addr in);

（一）inet_aton() 

轉換網路主機地址cp為二進位制數值，並存儲在struct in_addr結構中，即第二個引數*inp,函式返回非0表示cp主機有地有效，返回0表示主機地址無效。

       inet_aton() converts the Internet host address cp from the standard numbers-and-dots notation into binary data and stores it in the structure that inp points to. inet_aton() returns non-zero if the address is valid, zero if not.

（二）inet_addr

函式轉換網路主機地址（如192.168.1.10)為網路位元組序二進位制值，如果引數char *cp無效，函式返回-1(INADDR_NONE),這個函式在處理地址為255.255.255.255時也返回－1,255.255.255.255是一個有效的地址，不過inet_addr無法處理;

The inet_addr() function converts the Internet host address cp from numbers-and-dots notation into binary data in network byte order.   If the input is invalid, INADDR_NONE (usually -1) is returned. This is an

The inet_ntoa() function converts the Internet host address in given in network byte order to a string in standard numbers-and-dots notation. The string is returned in a statically allocated buffer, which subse

（三）inet_ntoa 

函式轉換網路位元組排序的地址為標準的ASCII以點分開的地址,,該函式返回指向點分開的字串地址的指標，該字串的空間為靜態分配的，這意味著在第二次呼叫該函式時，上一次呼叫將會被重寫（覆蓋），所以如果需要儲存該串最後複製出來自己管理！

The inet_ntoa() function converts the Internet host address in given in network byte order to a string in standard numbers-and-dots notation. The string is returned in a statically allocated buffer, which subsequent calls will overwrite.

（四）有兩個更新的函式inet_pton和inet_ntop這2個函式能夠處理ipv4和ipv6,原型如下

===============================================================================

    printf("%s \n", inet_ntoa(inp));

    printf("%x \n",inet_addr(ip));

}

// Internet address.
struct in_addr {
        union {
                struct { u_char s_b1,s_b2,s_b3,s_b4; } S_un_b;
                struct { u_short s_w1,s_w2; } S_un_w;
                u_long S_addr; /* port in network byte order */
        } S_un;
#define s_addr  S_un.S_addr
};
// Socket address, internet style.
struct sockaddr_in {        // struct sockaddr的一種特殊形式
        short            sin_family;    /* address family: AF_INET */
        u_short        sin_port;        /* port in network byte order */
        struct in_addr sin_addr;        /* port in network byte order */
        char            sin_zero[8];    /* 8 byte pad */
};
// Structure used by kernel to store most addresses.
struct sockaddr {
        u_short sa_family; /* address family */
        char    sa_data[14]; /* up to 14 bytes of direct address */
};

struct in_addr {
    unsigned long int s_addr;
}