Verify that there are at least n bits in an input stream

Hy Guys, I'm new in C++ and I Have a problem whit input file, I'm reading a file from the disk and I just can't read it until the end because at the end of the file there may be junk information.

My problem now is to find a function that verifies me if there are other X bits in the file otherwise, I stop because those for me are junk information

Sorry for my terrible English but I'm learning