Question

这是我的代码。

#include <stdio.h>
#include <stdlib.h>
#include <inttypes.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>

int main()
{
    struct addrinfo *ai, *p;

    if (getaddrinfo("localhost", "http", NULL, &ai) != 0) {
        printf("error\n");
        return EXIT_FAILURE;
    }

    for (p = ai; p != NULL; p = p->ai_next)
    {
        if (p->ai_family == AF_INET) {
            struct sockaddr_in *addr = (struct sockaddr_in *) p->ai_addr;
            printf("IPv4 port: %d\n", addr->sin_port);
        } else if (p->ai_family == AF_INET6) {
            struct sockaddr_in6 *addr = (struct sockaddr_in6 *) p->ai_addr;
            printf("IPv6 port: %d\n", addr->sin6_port);
        }
    }

    return 0;
}

这是输出。

$ gcc -std=c99 -D_POSIX_SOURCE -Wall -Wextra -pedantic foo.c
$ ./a.out 
IPv6 port: 20480
IPv6 port: 20480
IPv4 port: 20480
IPv4 port: 20480

我期待端口号为80.为什么我在输出中看到20480呢？

Answer 1

端口按网络顺序返回。尝试拨打#include <iostream> struct always_10 { constexpr static double value() { return 10.0; } }; template <class X> void show_x() { constexpr auto x = X::value(); std::cout<<"x is always "<< x <<" in the entire program."<<std::endl; } template<class X> void show_x(X x_) { constexpr auto x = x_.value(); std::cout<<"x is always "<< x <<" in the entire program."<<std::endl; } int main() { show_x<always_10>(); show_x(always_10()); return 0; }

请参见反向字节顺序：

0x5000 = 20480

0x0050 = 80

为什么getaddrinfo为HTTP返回端口号20480？

1 个答案: