协议不支持的地址族 [英] Address family not supported by protocol

问题描述

以下代码是TCP客户端的套接字编程示例.

Following code is a socket programming sample for a TCP client.

但是当我运行此命令时，connect()返回为协议不支持的地址族.

But when I run this, connect() is returned as Address family not supported by protocol.

我听说，如果平台不支持ipv6，则会出现此问题.

I have heard, this problem will happen if the platform does not support ipv6.

但是我写的AF_INET是ipv4.

But AF_INET I wrote is ipv4.

我的服务器CentOS6.4也在inet6 addr中配置.

Also my server, that is CentOS6.4, is configured within an inet6 addr .

有人知道为什么吗?

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

int
main(){
    struct sockaddr_in server;
    int sock;
    char buf[32];
    int n;
    sock = socket(AF_INET,SOCK_STREAM,0);
    perror("socket");
    server.sin_family = AF_INET;
    server.sin_port = htons(12345);
    inet_pton(AF_INET,"127.0.0.1",&server,sizeof(server));
    connect(sock,(struct sockaddr *)&server,sizeof(server));
    perror("connect");
    memset(buf,0,sizeof(buf));
    n = read(sock,buf,sizeof(buf));
    perror("read");
    printf("%d,%s\n",n,buf);
    close(sock);
    return 0;
}

推荐答案

代码将错误的目标地址和错误数量的参数传递给inet_pton(). (对于后者，编译器应该警告过您，顺便说一句)

The code passes the wrong destination address and wrong number of arguments to inet_pton(). (For the latter the compiler should have warned you about, btw)

此行

 inet_pton(AF_INET, "127.0.0.1", &server, sizeof(server));

应该是

 inet_pton(AF_INET, "127.0.0.1", &server.sin_addr);

逐字记录来自 man inet_pton :

Verbatim from man inet_pton:

int inet_pton(int af，const char * src，void * dst);

AF_INET

[...]地址被转换为 一个struct in_addr并复制到dst，该长度必须为sizeof(struct in_addr)(4)字节(32位)长.

[...] The address is converted to a struct in_addr and copied to dst, which must be sizeof(struct in_addr) (4) bytes (32 bits) long.

---

与问题无关，但也有问题，是read()返回ssize_t而不是int.

---

Not related to the problem, but also an issue, is that read() returns ssize_t not int.

以下行应调整:

int n;
[...]
printf("%d, %s\n", n, buf);

成为:

ssize_t n;
[...]
printf("%zd, %s\n", n, buf);

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