GCC 4.7 istream::tellg() returns -1 after reaching EOF

Question

The following code works with gcc 4.4.
But gcc 4.7 will give assertion failure.

#include 
#include 
#include 

        

Answer 1

To be precise, eofbit won't cause tellg() to return -1. But the fact that you read past EOF sets the failbit, and tellg() will return -1 if badbit or failbit are set.

The solution is to clear the status flags before calling tellg():

iss.clear();
iss.tellg();  // should work

Answer 2

According to C++11 section 27.7.2.3p40,

if fail() != false, returns pos_type(-1)

So gcc 4.7 has the correct behavior for the current version of C++ (assuming that peek() at end of stream causes failbit to be set, and it does during sentry construction, since skipws is set by default).

Looking at the wording of C++03, it is the same. 27.6.1.3p37. So the behavior you describe in gcc 4.4 is a bug.