getch returns 2 characters when I type one

问题:

When I use getch, it always appends the caracter read with a null character.

When I use the following code:

#include "stdafx.h"
#include <conio.h>

int main()
{
    char c = 0;

    while (c != 'x')
    {
        c = _getch();
        printf("Char read: <%c> \n", c);
    }
}

It returns the follwing on the console, when I press the keys "asdx":

Char read: <a>
Char read: < >
Char read: <s>
Char read: < >
Char read: <d>
Char read: < >
Char read: <x>

This is compiled in VS 2017 in a plain new single file project, running on a windows 10 console window. I tried removing the _UNICODE and UNICODE define.

回答1:

Well, crap!

It's a (rather new) bug in windows.

https://developercommunity.visualstudio.com/content/problem/247770/-getch-broken-in-vs-157.html

"When building a console application using the _getch() function suddenly returns two times for each keypress"

got the following response from microsoft:

" Thanks for reporting this! This will be fixed on a future windows update."

UPDATE: As stated in the link above, setting the runtime to statically link with a previous version of the C runtime will fix the issue, but you need to make sure all your related projects (if you are building a library, for example) also use the same runtime. (I tested it)

回答2:

If you don't want to (or you can't) use a previous version of the Universal C Runtime, you can use _getwch instead of _getch, as the problem doesn't affect to _getwch function.

Note that _getwch can return Unicode characters, so it may return distinct values than _getch for some keys. For example, for € character, _getch returns 0x3f (?) while _getwch returns 0x20ac (Unicode value for €)