Check for Empty sstream - c++

Question

I am wrote a function that can replace cin for integers and potentially doubles, that includes error checking capabilities. Using cin.fail() I was able to check for most cases, but that didn't cover the case where the input was followed by a string without a space. For example, "23tewnty-three." The following code accommodates this.
int getUserInt(string prompt = "Enter an integer: ", string errorMessage "Error: Invalid Input") {
const int IGNORE_MAX = 100;
int userInt = 0;
bool isContinue = true;
do {
// initialize and reset variables
string inputStr;
istringstream inputCheck;
userInt = 0;
// get input
cout << prompt;
cin >> inputStr;
inputCheck.str(inputStr);
// check for valid input
inputCheck >> userInt;
if (!inputCheck.fail()) {
// check for remaining characters
if (inputCheck.eof()) { // Edit: This is the section that I tried replacing with different code (made code compilable in response to comment)
isContinue = false;
}
else {
cout << errorMessage << endl;
}
}
else {
// reset cin and print error message
cin.ignore(IGNORE_MAX, '\n');
cin.clear();
cout << errorMessage << endl;
}
} while (isContinue);
return userInt;
}
This code works, but the reason I am posting this to Stack Overflow instead of Code Review is because my main question is about why some of code didn't work as I expected. The following is what I tried in place of inputCheck.eof() in the previous code. My questions are what are the differences between the following code? Why didn't methods 2) and 3) work? and which method is preferred?
inputCheck.eof()
inputCheck.peek() == EOF
inputCheck.str().empty()
inputCheck.rdbuf()->in_avail() == 0
1) and 4) worked as expected, but 2) and 3) did not.
Edit:
I believe 3) didn't work as expected because inputCheck.str() returns what was contained in inputStr when inputCheck.str(inputStr) was called. However, I have no idea why inputCheck.peek() == EOF didn't work.
If this is relevant information, I am compiling and running on windows through bash g++.

Answer 1

For every prompt you provide, you can expect your user to press Enter. Obtain input as a string, then try to convert. (Don’t try to convert from cin.)
Bonus: here’s a function to perform conversion.
template <typename T>
auto string_to( const std::string & s )
{
T value;
std::istringstream ss( s );
return ((ss >> value) and (ss >> std::ws).eof())
? value
: std::optional<T> { };
}
You’ll need C++17 for that, or to #include <boost/optional.hpp> instead.
Now:
std::cout << "Enter an integer! ";
std::string s;
getline( std::cin, s );
auto x = string_to <int> ( s );
if (!x)
{
std::cout << "That was _not_ an integer.\n";
}
else
{
std::cout << "Good job. You entered the integer " << *x << ".\n";
}
No more worrying about clearing or resetting cin. Handily perform some loops (such as allow user three attempts before quitting). Et cetera.