This question already has an answer here:
The istream operator>> is used to read the data and the function returns reference to istream.
For example,
istream& operator>> (bool& val);
But how does the istream is converted into a bool when it is used inside the conditional statement.
For example,
ifstream ifs(.....); // open the file
istream &is = (istream&)ifs;
char c;
if(is >> c) // how the istream is been evaluated into as bool
{
// character read
}
Can anyone explain how it is being converted into a bool inside a conditional expression?
From cppreference:
So since an if statement is a boolean context, it will invoke
std::istream
's member function operator.operator >> return a reference to istream (istream&).
and so you're actually writing if (istream) which is in turn calling the operator bool..
in conditionals 0 is false anything else is true -> istream has an opeartor bool that checks if the stream is ok so it will return !fail()...hence true.