Beej 的《网络编程指南》一书中的 showip.c 中的编译器错误（第 5.1 节）

Question

我正在尝试从 Beej 的网络编程书中学习网络编程。 5.1节有一段代码

/*
** showip.c -- show IP addresses for a host given on the command line
*/

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <netinet/in.h>

int main(int argc, char *argv[])
{
    struct addrinfo hints, *res, *p;
    int status;
    char ipstr[INET6_ADDRSTRLEN];

    if (argc != 2) {
        fprintf(stderr,"usage: showip hostname\n");
        return 1;
    }

    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC; // AF_INET or AF_INET6 to force version
    hints.ai_socktype = SOCK_STREAM;

    if ((status = getaddrinfo(argv[1], NULL, &hints, &res)) != 0) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(status));
        return 2;
    }

    printf("IP addresses for %s:\n\n", argv[1]);

    for(p = res;p != NULL; p = p->ai_next) {
        void *addr;
        char *ipver;

        // get the pointer to the address itself,
        // different fields in IPv4 and IPv6:
        if (p->ai_family == AF_INET) { // IPv4
            struct sockaddr_in *ipv4 = (struct sockaddr_in *)p->ai_addr;
            addr = &(ipv4->sin_addr);
            ipver = "IPv4";
        } else { // IPv6
            struct sockaddr_in6 *ipv6 = (struct sockaddr_in6 *)p->ai_addr;
            addr = &(ipv6->sin6_addr);
            ipver = "IPv6";
        }

        // convert the IP to a string and print it:
        inet_ntop(p->ai_family, addr, ipstr, sizeof ipstr);
        printf("  %s: %s\n", ipver, ipstr);
    }

    freeaddrinfo(res); // free the linked list

    return 0;
}

当我在 Ubuntu 终端中编译它时，出现以下错误

showip.c: In function ‘main’:
showip.c:15:25: error: storage size of ‘hints’ isn’t known
   15 |         struct addrinfo hints, *res, *p;
      |                         ^~~~~
showip.c:28:23: warning: implicit declaration of function ‘getaddrinfo’ [-Wimplicit-function-declaration]
   28 |         if ((status = getaddrinfo(argv[1], NULL, &hints, &res)) != 0) {
      |                       ^~~~~~~~~~~
showip.c:29:54: warning: implicit declaration of function ‘gai_strerror’; did you mean ‘strerror’? [-Wimplicit-function-declaration]
   29 |                 fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(status));
      |                                                      ^~~~~~~~~~~~
      |                                                      strerror
showip.c:29:48: warning: format ‘%s’ expects argument of type ‘char *’, but argument 3 has type ‘int’ [-Wformat=]
   29 |                 fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(status));
      |                                               ~^     ~~~~~~~~~~~~~~~~~~~~
      |                                                |     |
      |                                                |     int
      |                                                char *
      |                                               %d
showip.c:35:37: error: invalid use of undefined type ‘struct addrinfo’
   35 |         for(p = res;p != NULL; p = p->ai_next) {
      |                                     ^~
showip.c:41:22: error: invalid use of undefined type ‘struct addrinfo’
   41 |                 if (p->ai_family == AF_INET) { // IPv4
      |                      ^~
showip.c:42:75: error: invalid use of undefined type ‘struct addrinfo’
   42 |                         struct sockaddr_in *ipv4 = (struct sockaddr_in *)p->ai_addr;
      |                                                                           ^~
showip.c:46:77: error: invalid use of undefined type ‘struct addrinfo’
   46 |                         struct sockaddr_in6 *ipv6 = (struct sockaddr_in6 *)p->ai_addr;
      |                                                                             ^~
showip.c:52:28: error: invalid use of undefined type ‘struct addrinfo’
   52 |                 inet_ntop(p->ai_family, addr, ipstr, sizeof ipstr);
      |                            ^~
showip.c:56:9: warning: implicit declaration of function ‘freeaddrinfo’ [-Wimplicit-function-declaration]
   56 |         freeaddrinfo(res); // free the linked list
      |         ^~~~~~~~~~~~

我检查了他网站上给出的勘误表页面，但发现它没有帮助。似乎所有必需的库都包含在这里，所以我不知道错误的根源是什么。如果有人能指出，那就太好了。 谢谢

Answer 1

正如@stark提到的，addrinfo的存储大小未知应该有助于编译代码。

由于我没有足够的声誉来评论，关于运行时错误

getaddrinfo: Name or service not known

，您需要删除协议

https://

和终止正斜杠。

如果您查看

getaddrinfo

的联机帮助页：

node specifies either a
numerical network address (for IPv4, numbers-and-dots notation as
supported by inet_aton(3); for IPv6, hexadecimal string format as
supported by inet_pton(3)), or a network hostname

我们只需要主机名，不需要协议。所以你应该按如下方式运行该程序：

$ ./a.out www.google.com
IP addresses for www.google.com:

  IPv4: 142.251.163.106
...

事实上，如果您查看链接的页面，它会为您提供示例输出：

$ showip www.example.net
IP addresses for www.example.net:

  IPv4: 192.0.2.88

$ showip ipv6.example.com
IP addresses for ipv6.example.com:

  IPv4: 192.0.2.101
  IPv6: 2001:db8:8c00:22::171