Question

I am reading a std::istream and I need to verify without extracting characters that:

1. The stream is not "empty", i.e. that trying to read a char will not result in an fail state (solved by using peek() member function and checking fail state, then setting back to original state)

2. That among the characters left there is at least one which is not a space, a tab or a newline char.

The reason for this is, is that I am reading text files containing say one int per line, and sometimes there may be extra spaces / new-lines at the end of the file and this causes issues when I try get back the data from the file to a vector of int.

A peek(int n) would probably do what I need but I am stuck with its implementation.
I know I could just read istream like:

while (myInt << myIstream) {…} //Will fail when I am at the end 

but the same check would fail for a number of different conditions (say I have something which is not an int on some line) and being able to differentiate between the two reading errors (unexpected thing, nothing left) would help me to write more robust code, as I could write:

while (something_left(myIstream)) {
  myInt << myIstream;
  if (myStream.fail()) {…} //Horrible things happened
}

Thank you!

Answer 1

this is what I did to skip whitespace/detect EOF before the actual input:

char c;
if (!(cin >> c)) //skip whitespace
    return false;  // EOF or other error
cin.unget();

This is independent of what data you are going to read.

This code relies on the skipws manipulator being set by default for standard streams, but it can be set manually cin >> skipw >> c;