std::getline() returns

Question

I have a loop that reads each line in a file using getline():

istream is; string line; while (!getline(is, line).eof()) {     // ... } 

I noticed that calling getline() like this also seems to work:

while (getline(is, line)) 

What's going on here? getline() returns a stream reference. Is it being converted to a pointer somehow? Is this actually a good practice or should I stick to the first form?

Answer 1

The istream returned by getline() is having its operator void*() method implicitly called, which returns whether the stream has run into an error. As such it's making more checks than a call to eof().

Answer 2

Updated:

I had mistakenly pointed to the basic_istream documentation for the operator bool() method on the basic_istream::sentry class, but as has been pointed out this is not actually what's happening. I've voted up Charles and Luc's correct answers. It's actually operator void*() that's getting called. More on this in the C++ FAQ.