网络地址转换相关函数使用(inet_addr,inet_ntoa,inet_addr)

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相关函数原型及参数类型：

函数原型：
int inet_aton(const char *cp, struct in_addr *inp);

in_addr_t inet_addr(const char *cp);

in_addr_t inet_network(const char *cp);

char *inet_ntoa(struct in_addr in);

struct in_addr inet_makeaddr(int net, int host);

in_addr_t inet_lnaof(struct in_addr in);

in_addr_t inet_netof(struct in_addr in);

int inet_pton(int af, const char *src, void *dst);
       inet_pton()  returns  1 on success (network address was successfully converted).  0 is returned if src does not contain a character string representing a valid network address in the specified
       address family.  If af does not contain a valid address family, -1 is returned and errno is set to EAFNOSUPPORT.

参数类型：
/* Internet address.  */
typedef uint32_t in_addr_t;
struct in_addr
{
    in_addr_t s_addr;
};

inet_addr函数：将IPv4的点分十进制地址转换为网络字节序

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <arpa/inet.h>

int main(int argc, char *argv[])
{
    struct in_addr addr;

    if (argc != 2) {
        fprintf(stderr, "%s <dotted-address>\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    if (inet_aton(argv[1], &addr) == 0) {
        perror("inet_aton");
        exit(EXIT_FAILURE);
    }
    printf("addr = 0x%-10x\n", addr.s_addr);

    printf("%s\n", inet_ntoa(addr));
    exit(EXIT_SUCCESS);
}

yinguicai@Cpl-IBP-Product:~/tmp/network$ ./a.out 127.0.0.1
addr = 0x100007f   
127.0.0.1

char *inet_ntoa(struct in_addr in)
{
    static char buf[INET_NTOA_MAX_LEN];
    return inet_ntoa_r(in, buf);
}

注意：

1、inet_ntoa的返回值是一个static类型的char *指针，所以使用的时候需要注意(不可重入,可以使用线程安全的inet_ntoa_r函数代替)

2、The inet_addr() function converts the Internet host address cp from IPv4 numbers-and-dots notation into binary data in network byte order.  If the input is invalid, INADDR_NONE (usually -1) is
       returned.  Use of this function is problematic(有问题的) because -1 is a valid address (255.255.255.255).  Avoid its use in favor of inet_aton(), inet_pton(3), or getaddrinfo(3) which provide a  cleaner
       way to indicate error return.(因为其返回值为in_addr_t，当返回-1时，有二义性->表示两个含义)

3、inet_aton() returns nonzero if the address is valid, zero if not.

4、inet_aton/inet_addr/inet_ntoa仅适用于ipv4地址

5、inet_pton/inet_ntop对于v4和v6地址均适用