我对以下简单代码有两个问题：
/*
test.cpp
© BS.
Example of creation of a class of a flow for which it is possible to assign the additional
characters interpreted as separators.
11/06/2013, Раздел 11.7
*/
//--------------------------------------------------------------------------------------------------
#include <iostream>
#include <sstream>
#include <algorithm>
#include <exception>
#include <string>
#include <vector>
using namespace std;
//--------------------------------------------------------------------------------------------------
class Punct_stream
// it is similar to istream flow, but the user can independently set separators.
{
private:
istream& source; // source of chars
istringstream buffer; // buffer for formatting
string white; // whitespaces
bool sensitive; // case sensitive
public:
Punct_stream(istream& is): source(is), sensitive(true) {}
void whitespace(const string& s) { white = s; }
void add_white(char c) { white += c; }
void case_sensitive(bool b) { sensitive = b; }
bool is_case_sensitive() { return sensitive; }
bool is_whitespace(char c);
Punct_stream& operator >> (string& s);
operator bool();
};
//--------------------------------------------------------------------------------------------------
bool Punct_stream::is_whitespace(char c)
// is the c a whitespace?
{
for(int i = 0; i < white.size(); ++i) if(c == white[i]) return true;
return false;
}
//--------------------------------------------------------------------------------------------------
Punct_stream::operator bool()
// check the input result
{
return !(source.fail() || source.bad()) && source.good();
}
//--------------------------------------------------------------------------------------------------
Punct_stream& Punct_stream::operator >> (string& s){
while(!(buffer >> s)){ // try to read the data from the buffer
if(buffer.bad() || !source.good()) return *this;
buffer.clear();
string line;
getline(source,line); // read the line from the source
// if necessary we replace characters
for(int i = 0; i < line.size(); ++i)
if(is_whitespace(line[i])) line[i] = ' ';
else if(!sensitive) line[i] = tolower(line[i]);
buffer.str(line); // write a string line to the stream
}
return *this;
}
//==================================================================================================
int main()
// entry point
try{
Punct_stream ps(cin);
ps.whitespace(";:,.?!()\"{}<>/&$@#%^*|~");
ps.case_sensitive(false);
cout << "Enter the words, please: ";
vector<string> vs;
string word;
while(ps >> word) vs.push_back(word); // enter words
sort(vs.begin(), vs.end());
// we delete counterparts
for(int i = 0; i < vs.size(); ++i) if(i == 0 || vs[i] != vs[i-1]) cout << vs[i] << endl;
}
catch(exception& e){
cerr << e.what() << endl;
return 1;
}
catch(...){
cerr << "Unknown exception." << endl;
return 2;
}
Punct_stream::operator bool() 函数中的检查对我来说不清楚：
return !(source.fail() || source.bad()) && source.good();
我的问题：
为什么作者检查“失败”和“坏”？为什么不只限制“好”检查？除非积极的“好”不自动暗示，“失败”和“坏”设置在“假”值中？
此外，经常在代码中编写这样的结构：
cin >> x; while(cin){//...}
为什么作者没有如此类推：
Punct_stream::operator bool()
// check the input result
{
// return !(source.fail() || source.bad()) && source.good();
return source;
}
我显示的替代选项对我不起作用（Windows 崩溃），最好了解为什么，我错过了什么？
谢谢你。