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My task is to input individual characters , terminate the input with "space" or "ESC" and then retrieve / save the characters entered.
getchar and its variety waits in loop (?) and outputs to stdout until "enter" key is pressed.
putchar outputs ( to stdout) EACH character entered in do { ...} while loop - runs the loop.
Questions
1. Is there a way to terminate getchar other than entering "enter "?
2. How does putchar "runs" in do { .. } while loop ignoring getchar?
3. How can I "retrieve" characters in WHAT buffer for additional processing AFTER the do{} while loop is terminated ?
char next;
do
{
next = getchar(); putchar(next); }
while (next != '\n');
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Vaclav_ wrote: getchar and its variety waits in loop (?) and outputs to stdout until "enter" key is pressed.
No, getchar merely reads the next character entered at the terminal. If the terminal is in (normal) echo mode then it displays the character as typed. The putchar function merely displays a character, it has no knowledge of the loop or anything else.
1. Yes, you can terminate on anything, just inspect the character as entered and compare it to your terminator.
2. As above, putchar does nothing beyond displaying a single character.
3. Save them somewhere.
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I am seeing this
char next;
do
{
next = getchar(); cout << "text entered " << endl;
putchar(next); }
while (next != '\n');
qwerty
text entered
qtext entered
wtext entered
etext entered
rtext entered
ttext entered
ytext entered
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you need to turn off canonical mode on input. man termios, and look for ICANON. As a quick test without recompiling:
$ myprog
qwerty
text entered
qtext entered
wtext entered
etext entered
rtext entered
ttext entered
ytext entered
$ stty -icanon
$ myprog
qtext entered
qwtext entered
wetext entered
ertext entered
rttext entered
tytext entered
y
text entered
$ stty icanon
See: [FAQ - Cprogramming.com](https://faq.cprogramming.com/cgi-bin/smartfaq.cgi?answer=1045691686&id=1043284392)
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It seems that reading characters one at a time is no longer possible (on Windows). While getchar returns the characters one at a time, the system does not present them until after the enter key was pressed. So although you are trying to read single characters, they are still streamed internally.
[edit]
Same result on Ubuntu.
[/edit]
modified 16-Jun-19 13:01pm.
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It has nothing to do with windows 
Whoever writes the C/C++ library determines how it works, you are making a C/C++ standard call not a windows call and if they don't do the standard then it is hardly a fault of windows.
On windows really the easy way is to hook the WM_CHAR and/or WM_SYSCHAR messages because the message queue is available even in console apps since windows XP service pack 2.
In vino veritas
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I know that, I was merely pointing out its behaviour on Windows as opposed to Linux.
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Richard MacCutchan wrote: the system does not present them until after the enter key was pressed.
Not quite true, or at least not complete: if there is something in the input buffer already, getchar will immediately return with the next char it finds in that buffer. It will only wait if the input buffer is empty. AFAIK this is not dependend on the OS.
GOTOs are a bit like wire coat hangers: they tend to breed in the darkness, such that where there once were few, eventually there are many, and the program's architecture collapses beneath them. (Fran Poretto)
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Well that is exactly what happened in my tests, none of the characters were retrieved until the enter key was pressed.
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No it doesn't always it depends on the canonical mode of your input, this was covered above.
The C standard doesn't cover how the underlying system is operating and it cant present what it doesn't yet have.
Richard simply has an OS that is in canonical mode.
In vino veritas
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Well it always worked as I described for me. But I admit I haven't heard of the canonical mode before, so I'm going to trust you on this.
GOTOs are a bit like wire coat hangers: they tend to breed in the darkness, such that where there once were few, eventually there are many, and the program's architecture collapses beneath them. (Fran Poretto)
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Hi,
There are icon for Maximize and Restore Down on Wondow Title.
Can I change Maximize icon to Restore down on button click?
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I am processing the WM_MOUSEWHEEL messages in a C++ application,
void CView::OnMouseWheel(
HWND hWnd,
int xPos,
int yPos,
int zDelta,
UINT fwKeys
)
{
zDelta /= WHEEL_DELTA; if (zDelta != 0)
{
OnVScroll(hWnd, NULL, zDelta > 0 ? SB_LINEUP : SB_LINEDOWN, 3);
}
}
</blockquote>
but when I use the touchpad nothing happens. Following the advice in the MSDN documentation I divide the zDelta value by 120 (WHEEL_DELTA) to calculate the (approximate) number of lines to scroll. The debugger shows that the resulting value is always zero. If I use my mouse and turn the wheel it scrolls correctly. The weird part is that using other applications (VS, Word, Chrome etc.) the touchpad works correctly. So I conclude that the code should somehow get some other information that identifies the touchpad, and adjusts the delta accordingly. Anyone else seen similar problems?
[edit]
Thanks to David D's sugestion I modified the code to accumulate deltas that are less than the value of WHEEL_DELTA, thus:
static int myDelta = 0;
if (abs(zDelta) < WHEEL_DELTA)
{
myDelta += zDelta;
zDelta = myDelta;
}
zDelta /= WHEEL_DELTA; if (zDelta != 0)
{
myDelta = myDelta % WHEEL_DELTA; OnVScroll(hWnd, NULL, zDelta > 0 ? SB_LINEUP : SB_LINEDOWN, 3);
}
which works a treat.
Note that I use the value 3 for the number of lines to scroll. In a proper commercial application the code should use the value of the system parameter: SPI_GETWHEELSCROLLLINES.
[/edit]
modified 14-Jun-19 9:09am.
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I found the mouse wheel events specific to the "mouse wheel".
When using only touch (tablet swipe) I got the scrolling, but the "wheel event" that I used to detect "at bottom or top" no longer fires and I need to find something else. I think it now has to tie into a "view changing" and / or "view changed" event and / or manipulation started / ended.
(And I think a touchpad is treated as a "pointer" in Windows 10).
The Master said, 'Am I indeed possessed of knowledge? I am not knowing. But if a mean person, who appears quite empty-like, ask anything of me, I set it forth from one end to the other, and exhaust it.'
― Confucian Analects
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The messages are coming through correctly, but the delta value is always less than 120. That is unless I give a fast swipe from top to bottom of the pad. I have checked the parameters sent with the message and, apart from the delta value, they are the same for the mouse or the touchpad. More debugging required I expect.
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The touchpad is just a mouse to the system, but it sends WM_MOUSEWHEEL messages somewhat differently. I have added the solution to my original post.
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Glad you got it working.
Yes, "delta" is a double, so it has quite a range.
I needed the "Manipulation events" which give scroll direction and distance.
The Master said, 'Am I indeed possessed of knowledge? I am not knowing. But if a mean person, who appears quite empty-like, ask anything of me, I set it forth from one end to the other, and exhaust it.'
― Confucian Analects
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The strange thing was that using both the debugger and Spy++, I could not 'see' the multiple messages coming in. In both cases after a scroll gesture on the touchpad, they both showed just one message and then went back to the application window. So it as if the delta values were just too small.
BTW, thanks for your interest.
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Is your message loop receiving any other messages (e.g., WM_TOUCH) when the touch pad is being interacted with?
"One man's wage rise is another man's price increase." - Harold Wilson
"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons
"You can easily judge the character of a man by how he treats those who can do nothing for him." - James D. Miles
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Not sure about that, but thanks I will definitely check.
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No, it never gets WM_TOUCH. But see my update and solution.
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Hi,
Richard MacCutchan wrote: I divide the zDelta value by 120 (WHEEL_DELTA) to calculate the (approximate) number of lines to scroll.
While it is true that the many of the old mouse drivers sent WHEEL_DELTA in multiples of 120 that is not always the case for high-precision mice and touchpads.
You are probably getting values much smaller than 120. To fix your code you need to keep track of the delta modulo of +/- 120 in a static local or class variable and add/subtract the latest delta from the previous value.
I also observe that you are hard-coding the line count rather than retrieving the user preference via SystemParametersInfo with SPI_GETWHEELSCROLLLINES.
Best Wishes,
-David Delaune
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Randor wrote: you need to keep track of the delta
Thanks David, that works perfectly - simple when you know how. As to the fixed value, this is purely for personal use so I am not too concerned with system settings; although I notice that 3 is the default value.
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Richard MacCutchan wrote: Thanks David, that works perfectly
Looks good, although I do see a minor issue with your latest code.
You are dropping the remainder without the modulo operation. Rather than setting your delta to zero you should keep the remainder after scrolling with:
myDelta = myDelta % WHEEL_DELTA;
Such a precision loss is probably not a big deal for simply scrolling a text window. But let's make our code samples more correct.
Best Wishes,
-David Delaune
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