dev-cpp-users

[Dev-C++] Curiosity about CHOOSECOLOR.

[<ten...@ne...>]

  In the Win32 API reference it's claimed that when you want to use the 
lpCustColors of that structure, you shall provide a pointer to a 16 
COLORREF values.
So you shall do this:
LPCOLORREF rgbCust = (LPCOLORREF)GlobalAlloc(GPTR, 16 * sizeof(COLORREF));
And in the message where you want select a color through the common dialog
CHOOSECOLOR chc;
[...]
chc.lpCusrtColors = rgbCust;
if (!ChooseColor(&chc)){
[...]

When I do this I get that the first square of custom colors is 
initialized to a random color, not black, and if I select it, then when 
I want paint something I get a memory access violation.
Then I change rgbCust to point to 17 values.
The same happens.
Then I make it point to 17 and pass &rgbCust[1];
Now it works nice.
Then I make it point to 16 values and I pass &rgbCust[1]. It works.
So this is the problem: you pass the COLORREF array to the struct but it 
receives &rgbCust[-1] from the pointer you provide.

Re: [Dev-C++] Curiosity about CHOOSECOLOR.

[Zodiaq <zo...@ac...>]

Hello Carlos and all Dev-C++ users,

Wednesday, July 23, 2003, 7:07:33 PM, Carlos wrote as follows:

CGdM>   In the Win32 API reference it's claimed that when you want to use the 
CGdM> lpCustColors of that structure, you shall provide a pointer to a 16 
CGdM> COLORREF values.
CGdM> So you shall do this:
CGdM> LPCOLORREF rgbCust = (LPCOLORREF)GlobalAlloc(GPTR, 16 * sizeof(COLORREF));
CGdM> And in the message where you want select a color through the common dialog
CGdM> CHOOSECOLOR chc;
CGdM> [...]
CGdM> chc.lpCusrtColors = rgbCust;
CGdM> if (!ChooseColor(&chc)){
CGdM> [...]

CGdM> When I do this I get that the first square of custom colors is 
CGdM> initialized to a random color, not black, and if I select it, then when 
CGdM> I want paint something I get a memory access violation.
CGdM> Then I change rgbCust to point to 17 values.
CGdM> The same happens.
CGdM> Then I make it point to 17 and pass &rgbCust[1];
CGdM> Now it works nice.
CGdM> Then I make it point to 16 values and I pass &rgbCust[1]. It works.
CGdM> So this is the problem: you pass the COLORREF array to the struct but it 
CGdM> receives &rgbCust[-1] from the pointer you provide.

There is nothing strange when you do likt this (code from Platform SDK
AFAIR):
        CHOOSECOLOR cc;                 // common dialog box structure
        static COLORREF custClrs[ 16 ];
        // Initialize CHOOSECOLOR 
        ZeroMemory( &cc, sizeof( CHOOSECOLOR ));
        cc.lStructSize = sizeof( CHOOSECOLOR );
        cc.hwndOwner = main_hwnd;//main_hwnd is my var
        //cc.hInstance = hInstance;
        cc.rgbResult = chosen_color;//my global var for storing color
        cc.Flags = CC_ANYCOLOR | CC_RGBINIT | CC_FULLOPEN;
        cc.lpCustColors = custClrs;
        if( ChooseColor( &cc ) == TRUE )
        {
                chosen_color = cc.rgbResult;
                return TRUE;
        }
        return FALSE;


-- 
regards, Zodiaq