我在 cin.get() 中遗漏了什么吗？

Question

I'm learning cin.get() in C++ and I'm trying to echo two chars (including whitespace) back to the user.

While running the code, it doesn't echo out the inputs properly.

char letter1, letter2;

cout << "Enter Letters: ";
cin >> letter1 >> letter2;
cin.get(letter1);
cin.get(letter2);
cout << "letter1 is: " << letter1 << " end.\n";
cout << "letter2 is: " << letter2 << " end.\n";

I intend to input 2 and 3, however, it gives me a different result:

Input (I had to type 3 twice for some reason)

Enter  Letters:2
3
3

Output

letter1 is:
end.
letter2 is: 3 end.

Answer 1

The formatted input operators skip leading whitespace (unless doing so is explicitly disabled, eg, using in >> std::noskipws; ). The unformatted input functions do not skip leading whitespace. As a result, the first use of std::cin.get(letter1) reads the newline character and the second use reads the entered digit.

You can explicitly skip leading whitespace, eg:

if ((std::cin >> std::ws).get(letter1)) {
    std::cout << “read ‘“ << letter1 << “‘\n”;
else {
    std::cout << “failed to read a character\n”;
}

The example also added some basic error handling: input should always be expected to fail and failures need to be handled appropriately. Obviously, failures need to be checked after the attempt to read input.