c++ good() eof() fail() bad()

// fortest.cpp : 定义控制台应用程序的入口点。//#include "stdafx.h"#include <string>#include <string.h>#include <map>#include <iostream>#include <stdio.h>#include <stdlib.h>#include <sstream>int main(){std::istringstream is("123");std::cout << "--------------------读取一个\n";is.get();std::cout << is.good() << std::endl;std::cout << is.eof() << std::endl;std::cout << is.fail() << std::endl;std::cout << is.bad() << std::endl;std::cout << "--------------------读取剩下的\n";char *buf = (char *)malloc(3 + 1);memset(buf, 0, 4);is.read(buf, 2);printf("%s\n", buf);std::cout << is.good()<< std::endl;std::cout << is.eof() << std::endl;std::cout << is.fail() << std::endl;std::cout << is.bad()<<std::endl;std::cout << "--------------------再读取\n";is.get();std::cout << is.good() << std::endl;std::cout << is.eof() << std::endl;std::cout << is.fail() << std::endl;std::cout << is.bad() << std::endl;std::cout << "--------------------再读取\n";is.get();std::cout << is.good() << std::endl;std::cout << is.eof() << std::endl;std::cout << is.fail() << std::endl;std::cout << is.bad() << std::endl;free(buf);    return 0;}/*--------------------读取一个1000--------------------读取剩下的231000--------------------再读取0110--------------------再读取0110请按任意键继续. . .*/