函数对比

函数	功能	头文件(Linux)	原型	源码实现
inet_ntop	convert IPv4 and IPv6 addresses from binary to text form	arpa/inet.h	const char inet_ntop(int af, const void src, char *dst, socklen_t size);	here
inet_ntoa	converts the Internet host address in, given in network byte order, to a string in IPv4 dotted-decimal notation. The string is returned in a statically allocated buffer, which subsequent calls will overwrite.	arpa/inet.h	char *inet_ntoa(struct in_addr in);	here
inet_addr	converts the Internet host address cp from IPv4 numbers-and-dots notation into binary data in network byte order.	arpa/inet.h	in_addr_t inet_addr(const char *cp);	封装了inet_ntoa
inet_pton	convert IPv4 and IPv6 addresses from text to binary form	arpa/inet.h	int inet_pton(int af, const char src, void dst);	here
inet_aton	converts the Internet host address cp from the IPv4 numbers-and-dots notation into binary form (in network byte order) and stores it in the structure that inp points to.	arpa/inet.h	int inet_aton(const char cp, struct in_addr inp);

inet_ntoa() 在内部使用了static 数组存储IP，有两个问题：

1.在一个语句中两次以上调用 inet_ntoa ，会输出同样的IP地址，如： printf("src=%s, dst=%s\n", inet_ntoa(src), inet_ntoa(dst));

2.经常出现段错误

推荐使用inet_pton/inet_ntop

网络地址sockaddr_in

    #include <netinet/in.h>

    struct sockaddr_in {
        short            sin_family;    
        unsigned short   sin_port;  
        struct in_addr   sin_addr;      
        char             sin_zero[8];  // 填充对齐
    };

    typedef uint32_t in_addr_t;

    struct in_addr {
        in_addr_t s_addr;
    };

    struct sockaddr {
           sa_family_t sa_family;
           char        sa_data[14];
       };

sockaddr 的作用？

int bind(int sockfd, const struct sockaddr *addr, socklen_t addrlen);
The only purpose of sockaddr is to cast the structure pointer passed in addr in order to avoid compiler warnings.

bind()作为一个标准接口，不仅接受Network socket address参数，还有下面两种，传参时避免编译警告。

• 用于进程间通信的 UNIX socket address 结构是

    struct sockaddr_un {
    sa_family_t sun_family;               /* AF_UNIX */
    char        sun_path[108];            /* pathname */
  };
  

示例： https://goo.gl/XpBgoh

• 用于内核与用户空间通信的Netlink socket address结构是

  struct sockaddr_nl {
    sa_family_t     nl_family;  /* AF_NETLINK */
    unsigned short  nl_pad;     /* Zero. */
    pid_t           nl_pid;     /* Port ID. */
    __u32           nl_groups;  /* Multicast groups mask. */
  };
  

示例程序

• inet_aton

    struct sockaddr_in myaddr;
    int s;
    
    myaddr.sin_family = AF_INET;
    myaddr.sin_port = htons(3490);
    inet_aton("63.161.169.137", &myaddr.sin_addr.s_addr);
    
    s = socket(PF_INET, SOCK_STREAM, 0);
    bind(s, (struct sockaddr*)myaddr, sizeof(myaddr));

• inet_ntoa

   #define _BSD_SOURCE
   #include <arpa/inet.h>
   #include <stdio.h>
   #include <stdlib.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) {
           fprintf(stderr, "Invalid address\n");
           exit(EXIT_FAILURE);
       }
  
       printf("%s\n", inet_ntoa(addr));
       exit(EXIT_SUCCESS);
   }
  

• inet_ntop & inet_pton

   #include <arpa/inet.h>
   #include <stdio.h>
   #include <stdlib.h>
   #include <string.h>
  
   int
   main(int argc, char *argv[])
   {
       unsigned char buf[sizeof(struct in6_addr)];
       int domain, s;
       char str[INET6_ADDRSTRLEN];
  
       if (argc != 3) {
           fprintf(stderr, "Usage: %s {i4|i6|<num>} string\n", argv[0]);
           exit(EXIT_FAILURE);
       }
  
       domain = (strcmp(argv[1], "i4") == 0) ? AF_INET :
                (strcmp(argv[1], "i6") == 0) ? AF_INET6 : atoi(argv[1]);
  
       s = inet_pton(domain, argv[2], buf);
       if (s <= 0) {
           if (s == 0)
               fprintf(stderr, "Not in presentation format");
           else
               perror("inet_pton");
           exit(EXIT_FAILURE);
       }
  
       if (inet_ntop(domain, buf, str, INET6_ADDRSTRLEN) == NULL) {
           perror("inet_ntop");
           exit(EXIT_FAILURE);
       }
  
       printf("%s\n", str);
  
       exit(EXIT_SUCCESS);
   }
  

参考

• man7.org