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0

Part of the code:

LRESULT CALLBACK WindowProc(
 _In_ HWND hwnd,
 _In_ UINT uMsg,
 _In_ WPARAM wParam,
 _In_ LPARAM lParam)
 ...
 switch(uMsg)
 ...
 case WM_SYSKEYDOWN:
 case WM_SYSKEYUP:
 case WM_KEYDOWN:
 case WM_KEYUP:
 
 uint8_t VKCODE = wParam;
 bool WasDown = ((lParam & (1<<30)) != 0);
 bool IsDown = ((lParam & (1<<31)) == 0);
 if(WasDown != IsDown)
 
 if(VKCode == 'W')
 
 OutputDebugStringA("W: ");
 if(WasDown)
 
 OutputDebugStringA("WasDown ");
 
 if(IsDown)
 
 OutputDebugStringA("IsDown ");
 
 OutputDebugStringA("n");
 
 else if(VKCode == 'A')
 
 OutputDebugStringA("An");
 
 ...
 
 break;
 ...
 
 ...

1) First, when I press 'A', will always output 2 'A's.

2) Second, according to this page:
https://docs.microsoft.com/en-us/windows/desktop/inputdev/wm-keyup

30 The previous key state. The value is always 1 for a WM_KEYUP message.

31 The transition state. The value is always 1 for a WM_KEYUP message.

then (lParam & (1<<31)) will always be non-zero, so IsDown will always be false, but when I press(hit and release) 'W' it will output:

IsDown
WasDown

How come it will output "IsDown" if bool IsDown is always false?

3) If I comment out 3 cases before WM_KEYUP like this:

// case WM_SYSKEYDOWN:
// case WM_SYSKEYUP:
// case WM_KEYDOWN:

then when I press 'A' will only output one 'A', when I press 'W' will only output "WasDown", never "IsDown". I didn't wrote any code under previous 3 cases before comment them out anyway, what happened?

BTW, I'm following this video if anyone wants to see the full code:

https://www.youtube.com/watch?v=J3y1x54vyIQ

c++ windows winapi windows-messages

share|improve this question

edited Mar 28 at 10:31

oNion

asked Mar 28 at 10:23

oNionoNion

4511 silver badge88 bronze badges

• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  
  From what you say under point 3 it sounds like you don't quite understand how case statements work in C/C++. The way you have your code structured, all four messages will be processed the same way. As far as #2 goes, bit 30 and 31 are always 1 for WM_KEYUP but for WM_KEYDOWN bit 30 can be 0 or 1 and bit 31 is always 0.
  
  – Jonathan Potter
  Mar 28 at 10:38
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @JonathanPotter So when I press a key, WindowProc process the message for WM_KEYDOWN and WM_KEYUP with the same block of code under case KEY_UP?
  
  – oNion
  Mar 28 at 10:44
  

  
  
  
  


• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  Yes, because when you have multiple case statements without a break in between them, control will flow through them from the matching case to the next break.
  
  – Jonathan Potter
  Mar 28 at 10:48
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  cboard.cprogramming.com/cplusplus-programming/…
  
  – David Heffernan
  Mar 28 at 10:52
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @oNion general advice: before trying to make Windows programs you should get familiar with the basics of the C language.
  
  – Jabberwocky
  Mar 28 at 12:41
  

  
  
  
  

 | 
show 1 more comment

0

Part of the code:

LRESULT CALLBACK WindowProc(
 _In_ HWND hwnd,
 _In_ UINT uMsg,
 _In_ WPARAM wParam,
 _In_ LPARAM lParam)
 ...
 switch(uMsg)
 ...
 case WM_SYSKEYDOWN:
 case WM_SYSKEYUP:
 case WM_KEYDOWN:
 case WM_KEYUP:
 
 uint8_t VKCODE = wParam;
 bool WasDown = ((lParam & (1<<30)) != 0);
 bool IsDown = ((lParam & (1<<31)) == 0);
 if(WasDown != IsDown)
 
 if(VKCode == 'W')
 
 OutputDebugStringA("W: ");
 if(WasDown)
 
 OutputDebugStringA("WasDown ");
 
 if(IsDown)
 
 OutputDebugStringA("IsDown ");
 
 OutputDebugStringA("n");
 
 else if(VKCode == 'A')
 
 OutputDebugStringA("An");
 
 ...
 
 break;
 ...
 
 ...

1) First, when I press 'A', will always output 2 'A's.

2) Second, according to this page:
https://docs.microsoft.com/en-us/windows/desktop/inputdev/wm-keyup

30 The previous key state. The value is always 1 for a WM_KEYUP message.

31 The transition state. The value is always 1 for a WM_KEYUP message.

then (lParam & (1<<31)) will always be non-zero, so IsDown will always be false, but when I press(hit and release) 'W' it will output:

IsDown
WasDown

How come it will output "IsDown" if bool IsDown is always false?

3) If I comment out 3 cases before WM_KEYUP like this:

// case WM_SYSKEYDOWN:
// case WM_SYSKEYUP:
// case WM_KEYDOWN:

then when I press 'A' will only output one 'A', when I press 'W' will only output "WasDown", never "IsDown". I didn't wrote any code under previous 3 cases before comment them out anyway, what happened?

BTW, I'm following this video if anyone wants to see the full code:

https://www.youtube.com/watch?v=J3y1x54vyIQ

c++ windows winapi windows-messages

share|improve this question

edited Mar 28 at 10:31

oNion

asked Mar 28 at 10:23

oNionoNion

4511 silver badge88 bronze badges

• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  
  From what you say under point 3 it sounds like you don't quite understand how case statements work in C/C++. The way you have your code structured, all four messages will be processed the same way. As far as #2 goes, bit 30 and 31 are always 1 for WM_KEYUP but for WM_KEYDOWN bit 30 can be 0 or 1 and bit 31 is always 0.
  
  – Jonathan Potter
  Mar 28 at 10:38
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @JonathanPotter So when I press a key, WindowProc process the message for WM_KEYDOWN and WM_KEYUP with the same block of code under case KEY_UP?
  
  – oNion
  Mar 28 at 10:44
  

  
  
  
  


• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  Yes, because when you have multiple case statements without a break in between them, control will flow through them from the matching case to the next break.
  
  – Jonathan Potter
  Mar 28 at 10:48
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  cboard.cprogramming.com/cplusplus-programming/…
  
  – David Heffernan
  Mar 28 at 10:52
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @oNion general advice: before trying to make Windows programs you should get familiar with the basics of the C language.
  
  – Jabberwocky
  Mar 28 at 12:41
  

  
  
  
  

 | 
show 1 more comment

Part of the code:

LRESULT CALLBACK WindowProc(
 _In_ HWND hwnd,
 _In_ UINT uMsg,
 _In_ WPARAM wParam,
 _In_ LPARAM lParam)
 ...
 switch(uMsg)
 ...
 case WM_SYSKEYDOWN:
 case WM_SYSKEYUP:
 case WM_KEYDOWN:
 case WM_KEYUP:
 
 uint8_t VKCODE = wParam;
 bool WasDown = ((lParam & (1<<30)) != 0);
 bool IsDown = ((lParam & (1<<31)) == 0);
 if(WasDown != IsDown)
 
 if(VKCode == 'W')
 
 OutputDebugStringA("W: ");
 if(WasDown)
 
 OutputDebugStringA("WasDown ");
 
 if(IsDown)
 
 OutputDebugStringA("IsDown ");
 
 OutputDebugStringA("n");
 
 else if(VKCode == 'A')
 
 OutputDebugStringA("An");
 
 ...
 
 break;
 ...
 
 ...

1) First, when I press 'A', will always output 2 'A's.

2) Second, according to this page:
https://docs.microsoft.com/en-us/windows/desktop/inputdev/wm-keyup

30 The previous key state. The value is always 1 for a WM_KEYUP message.

31 The transition state. The value is always 1 for a WM_KEYUP message.

then (lParam & (1<<31)) will always be non-zero, so IsDown will always be false, but when I press(hit and release) 'W' it will output:

IsDown
WasDown

How come it will output "IsDown" if bool IsDown is always false?

3) If I comment out 3 cases before WM_KEYUP like this:

// case WM_SYSKEYDOWN:
// case WM_SYSKEYUP:
// case WM_KEYDOWN:

then when I press 'A' will only output one 'A', when I press 'W' will only output "WasDown", never "IsDown". I didn't wrote any code under previous 3 cases before comment them out anyway, what happened?

BTW, I'm following this video if anyone wants to see the full code:

https://www.youtube.com/watch?v=J3y1x54vyIQ

c++ windows winapi windows-messages

share|improve this question

edited Mar 28 at 10:31

oNion

asked Mar 28 at 10:23

oNionoNion

4511 silver badge88 bronze badges

LRESULT CALLBACK WindowProc(
 _In_ HWND hwnd,
 _In_ UINT uMsg,
 _In_ WPARAM wParam,
 _In_ LPARAM lParam)
 ...
 switch(uMsg)
 ...
 case WM_SYSKEYDOWN:
 case WM_SYSKEYUP:
 case WM_KEYDOWN:
 case WM_KEYUP:
 
 uint8_t VKCODE = wParam;
 bool WasDown = ((lParam & (1<<30)) != 0);
 bool IsDown = ((lParam & (1<<31)) == 0);
 if(WasDown != IsDown)
 
 if(VKCode == 'W')
 
 OutputDebugStringA("W: ");
 if(WasDown)
 
 OutputDebugStringA("WasDown ");
 
 if(IsDown)
 
 OutputDebugStringA("IsDown ");
 
 OutputDebugStringA("n");
 
 else if(VKCode == 'A')
 
 OutputDebugStringA("An");
 
 ...
 
 break;
 ...
 
 ...

IsDown
WasDown

// case WM_SYSKEYDOWN:
// case WM_SYSKEYUP:
// case WM_KEYDOWN:

share|improve this question

edited Mar 28 at 10:31

oNion

asked Mar 28 at 10:23

oNionoNion

4511 silver badge88 bronze badges

share|improve this question

edited Mar 28 at 10:31

oNion

asked Mar 28 at 10:23

oNionoNion

4511 silver badge88 bronze badges

asked Mar 28 at 10:23

oNionoNion

4511 silver badge88 bronze badges

asked Mar 28 at 10:23

oNionoNion

4511 silver badge88 bronze badges