套接字编程，将sockaddr_in转换为sockaddr。为什么？

Question

#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>
#define PORT 8080
int main ( int argument, char const *argv[] )
{
int obj_socket = 0, reader;
struct sockaddr_in serv_addr;
char *message = "A message from Client !";
char buffer[1024] = {0};
if (( obj_socket = socket (AF_INET, SOCK_STREAM, 0 )) < 0)
{
printf ( "Socket creation error !" );
return -1;
}
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(PORT);
if(inet_pton ( AF_INET, "127.0.0.1", &serv_addr.sin_addr)<=0)
{
printf ( "\nInvalid address ! This IP Address is not supported !\n" );
return -1;
}
if ( connect( obj_socket, (struct sockaddr *)&serv_addr, sizeof(serv_addr )) < 0) // <--- QUESTION ABOUT THIS LINE
{
Printf ( "Connection Failed : Can't establish a connection over this socket !" );
return -1;
}
send ( obj_socket , message , strlen(message) , 0 );
printf ( "\nClient : Message has been sent !\n" );
reader = read ( obj_socket, buffer, 1024 );
printf ( "%s\n",buffer );
return 0;
}

我一直在阅读文档并遍历头文件以理解结构，然而，还有最后一件事我无法获得。

头定义sockaddr结构，该结构至少包括以下成员:sa_family_t、sa_family address family char、SA_Data[]套接字地址（可变长度数据）

标头应定义sockaddr_in结构，该结构应至少包括以下成员:sa_family_t sin_family AF_INET。in_port_t sin_port端口号。结构in_addr sin_addr IP地址。

if ( connect( obj_socket, (struct sockaddr *)&serv_addr, sizeof(serv_addr )) < 0)

Answer 1

这里的这个铸造的目的是什么，它把sockaddr_in铸造成sockaddr。

sockaddr_in未被种姓为sockaddr。sockaddr_in*被种姓为sockaddr*。

执行强制转换是因为正在调用的函数connect不接受sockaddr_in*参数，而是接受sockaddr*参数。