C ++->>运算符如何工作？

Question

I have a question regarding the >> operator.
I wrote a program to count number of words in a binary file.
My question is about the while loop, shouldn't the >> read the space, go into the loop, increment c, but just not put anything into w ?
It gives me an output of 4, but counting the spaces shouldn't it be 10?
Any help is appreciated. My code is below:

#include<iostream.h>
#include<conio.h>
#include<fstream.h>
ofstream a;
ifstream b;
void main()
{
    clrscr();
    char w[20];
    a.open("newf.txt",ios::binary);
    a<<"This  is an   example\n";
    a.close();
    b.open("newf.txt");
    int c=0;
    while(b>>w)
    { 
        c++ ;
    }
    cout<<c;
    b.close();
    getch();  
}

Answer 1

By default the operator>> in ifstream ignores the whitespaces. If you want the whitespaces to be included, you have to use the std::noskipws manipulator flag as shown in the official documentation here .

Answer 2

First off, you're extracting into char w[20] don't do this . If a sting longer than 20 character is extracted bad things will happen. Instead use string w .

string::operator>> is what is called by b >> w which will:

Behaves as a FormattedInputFunction. After constructing and checking the sentry object, which may skip leading whitespace, first clears str with str.erase() , then reads characters from is and appends them to str as if by str.append(1, c) , until one of the following conditions becomes true:

• N characters are read, where N is is.width() if is.width() > 0 , otherwise N is str.max_size()
• the end-of-file condition occurs in the stream is
• std::isspace(c,is.getloc()) is true for the next character c in is (this whitespace character remains in the input stream).

If no characters are extracted then std::ios::failbit is set on is , which may throw std::ios_base::failure .

Finally, calls os.width(0) to cancel the effects of std::setw , if any.