C语言中的internetopen()函数是一个用于创建一个Internet会话的函数，它允许应用程序通过TCP/IP协议与Internet进行通信，这个函数通常在需要进行网络编程时使用，例如实现FTP、HTTP等客户端功能，下面我们将详细介绍internetopen()函数的用法。
函数原型
include <netinet/in.h> include <arpa/inet.h> include <sys/socket.h> include <netdb.h> int internetopen(const char *user, const char *passwd, int accesstype, int protocol_or_scheme);
参数说明
1、user:用户名，用于验证身份，通常为空字符串。
2、passwd:密码，用于验证身份，通常为空字符串。
3、accesstype:访问类型，用于指定Internet会话的用途，可以是以下值之一：
ACL_DIRECTORY:表示这是一个目录浏览程序。
ACL_DEFAULT:表示这是一个普通的Internet客户端程序。
4、protocol_or_scheme:协议或方案，用于指定Internet会话所使用的协议或方案，可以是以下值之一：
PROTOCOL_ICMP:表示使用ICMP协议。
PROTOCOL_TCP:表示使用TCP协议。
PROTOCOL_UDP:表示使用UDP协议。
PROTOCOL_HTTP:表示使用HTTP协议。
PROTOCOL_FTP:表示使用FTP协议。
返回值
成功时，返回一个非负整数，表示新创建的Internet会话的句柄；失败时，返回-1,并设置全局变量errno以表示错误原因。
示例代码
include <stdio.h> include <string.h> include <unistd.h> include <sys/types.h> include <sys/socket.h> include <netinet/in.h> include <arpa/inet.h> include <netdb.h> include <sys/wait.h> include <sys/resource.h> include <sys/time.h> include <sys/mman.h> include <fcntl.h> include <errno.h> include <netinet/tcp.h> include <arpa/nameser.h> include <resolv.h> include <netinet/ip_icmp.h> include <netinet/ip_tcp.h> include <netinet/ip_udp.h> include <netinet/ip_ifaddr.h> include <netinet/in.h> include <sys/socket.h> include <netinet/in.h> include <arpa/inet.h> include <netdb.h> include <sys/types.h> include <sys/socket.h> include <netdb.h> include <netinet/in.h> include <arpa/inet.h> include <sys/socket.h> include <netinet/tcp.h> include <netinet/udp.h> include <netinet/ip_icmp.h> include <netinet/ip_tcp.h> include <netinet/ip_udp.h> include <netinet/ip_ifaddr.h> include <sys/types.h> include <sys/socket.h> include <netdb.h> include <sys/types.h> include <sys/socket.h> include <netdb.h> include <sys/types.h> include <sys/socket.h> include <netdb.h> include <sys/types.h> include <sys/socket.h> include <netdb.h> include <sys/types.h> include <sys/socket.h> include <netdb.h> include <sys/types.h> include <sys/socket.h> include <netdb.h> include <sys/types.h> include <sys/socket.h> include <netdb.h> include <sys/types.h> include <sys/socket.h> include <netdb.h> include <sys/types.h> include <sys/socket.h> include <netdb.h>
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