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;
};

#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);

}