linux下检测本机是否可以上网

首先，本机PC需是直连接网络，没有设置代理，代码如下：

#include<stdio.h>
#include<netdb.h>
#include<string.h>

#define PORT 80

int main()
{
	struct hostent* host = NULL;
	host = gethostbyname("www.baidu.com");
	if(NULL == host)
	{
		printf("don't connect internet...");
		return -1;
	}
	///定义sockfd
	 int sock_cli = -1;
	 sock_cli = socket(AF_INET,SOCK_STREAM, 0);

	 ///定义sockaddr_in
	 struct sockaddr_in servaddr;
	 memset(&servaddr, 0, sizeof(servaddr));
	 servaddr.sin_family = AF_INET;
	 servaddr.sin_port = htons(PORT);  ///服务器端口
	 //servaddr.sin_addr.s_addr = inet_addr();  ///服务器ip
	 servaddr.sin_addr = *((struct in_addr *)host->h_addr);

	 ///连接服务器，成功返回0，错误返回-1
	 if (connect(sock_cli, (struct sockaddr *)&servaddr, sizeof(servaddr)) < 0)
	 {
		 perror("connect");
		 return -1;
	 }
	 else
	 {
		 printf("connect internet...");
	 }
	 return 0;
}