读取文件中的Eof位

Question

When i have something like this

ifstream f("file.txt");
int z=0;
while(f>>z)
cout<<z<<"\n";

I was asking in that while for which field it is looking to continue? For rdstate to evaluate if eof bit is set? And for any field that is set except good bit that rdstate is set to non-zero value?

Answer 1

while(f>>z)
    cout<<z<<"\n";

In this the operator >>() returns an ifstream& . That ifstream has an operator bool() that will return true as long as no error flags are set.

So for every successful read f>>z evaluates to true and you continue the loop. As soon as you get a bad read( data type mismatch, end of file, stream error) then f>>z evaluates to false the the loop ends.

The stream states that ifstream has are:

goodbit no error
badbit  irrecoverable stream error
failbit input/output operation failed (formatting or extraction error)
eofbit  associated input sequence has reached end-of-file