FlushConsoleInputBuffer

Hi,

I have some problems flushing the input buffer of a console using the FlushConsoleInputBuffer function. It just doesn't seem to work, even if the function return success. Maybe my vision of what is an input buffer is wrong (i always thought that if characters aren't return to you by a read function, they are considered still being in the input buffer; at least, that's how it "works" with the standard C functions). So... why isn't it working ? I'm quite lost.

Here's a simple test program i did, trying to find out what was wrong

Code:

---

#include <windows.h>
#include <string.h>

#define ERR() MessageBoxA(NULL, "Something went wrong somewhere", "Error", MB_OK)

int WINAPI WinMain(HINSTANCE hI, HINSTANCE hPI, LPSTR lpCL, int nCS)
{
    HANDLE stdOutputHandle;
    HANDLE stdInputHandle;
    DWORD dw;
    BOOL b;
    char c;

    const char *msg1 = "Enter 'q' to quit.";

    if (AllocConsole() != 0)
    {
        /* A: Houston, we have a console */

        stdOutputHandle = GetStdHandle(STD_OUTPUT_HANDLE);
        if (stdOutputHandle == INVALID_HANDLE_VALUE)
            ERR();
        stdInputHandle = GetStdHandle(STD_INPUT_HANDLE);
        if (stdInputHandle == INVALID_HANDLE_VALUE)
            ERR();

        do
        {
            WriteConsoleA(stdOutputHandle, msg1, strlen(msg1), &dw, NULL);
            if (dw != strlen(msg1))
                ERR();

            ReadConsoleA(stdInputHandle, &c, 1, &dw, NULL);
            if (dw != 1)
                ERR();

            if (FlushConsoleInputBuffer(stdInputHandle) == 0)
                ERR();
        } while (c != 'q');

        FreeConsole();
    }

    return 0;
}

---

As for the compiler, I'm using Visual Studio 2005 Pro.

Thanks

Perhaps you'd like to tell us what the error code is from your function, using GetLastError()?

--
Mats

Well, every function return "success". So there's no error code to show, except if I'm missing something. :confused:

You should learn how to use PCH, since including windows.h everytime you compile is pretty painful :)

Quote:

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Originally Posted by foxman

Well, every function return "success". So there's no error code to show, except if I'm missing something. :confused:

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So, what are you then saying is not working as you expect?

--
Mats

If you call GetNumberOfConsoleInputEvents before and after FlushConsoleInputBuffer you will see that as it is stated in the description the Flush does remove the InputEvents from buffer

Quote:

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So, what are you then saying is not working as you expect?

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As I saw it - If you press " \n" when asking to input something

ReadConsoleA reads one byte, but on the next iteration it continues to read next char, so it seems that input buffer was not cleared as expected (and in the same time GetNumberOfConsoleInputEvents returns 0). It seems to me ReadConsoleA buffers the current input event buffer somehow, so it is already remove from the queue.

Quote:

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Originally Posted by matsp

So, what are you then saying is not working as you expect?

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Well i was expecting the FlushConsoleInputBuffer function to flush the input buffer, but it's not doing it the way i was thinking.

Example, if i enter "hello" when ask to enter something, the ReadConsoleFunction will return me the 'h' in the car variable on the first iteration, then 'e' at the second iteration, etc, where i was expecting the FlushConsoleInputBuffer function to remove all this stuff so i could enter something on the next iteration.

From what i saw from vart explanation, the Flush function does remove something from the input buffer, but what, i don't know lol (i would need to check this out but i don't have the time right now), but i do know it's not removing what i wanted it to remove (the characters).

Anyway, thanks for the replies everyone. Guess I'll just empty the buffer (or whatever you want to call it) by making repetitive call to ReadConsole until the '\n' character is reached.

I noticed that FlushConsoleInputBuffer() is a "Low-Level Console Input Function", and ReadConsole() is a "High-Level Console Input Function" - perhaps one doesn't affect the other?

Would be interesting to see if any of the "High-Level Console Modes" changes this behavior.

gg