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GeneralRe: Accessing HDD drive Pin
Richard MacCutchan19-Apr-20 3:25
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GeneralRe: Accessing HDD drive Pin
_Flaviu19-Apr-20 8:48
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GeneralRe: Accessing HDD drive Pin
JudyL_MD19-Apr-20 4:31
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Questionvoid type Pin
CalinNegru(fearless_)10-Apr-20 22:20
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AnswerRe: void type Pin
Richard MacCutchan10-Apr-20 22:25
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GeneralRe: void type Pin
CalinNegru(fearless_)10-Apr-20 22:44
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GeneralRe: void type Pin
Richard MacCutchan10-Apr-20 23:18
mveRichard MacCutchan10-Apr-20 23:18 
GeneralRe: void type Pin
Member 798912211-Apr-20 1:22
MemberMember 798912211-Apr-20 1:22 
Your struct contains one int and one pointer. If the second member said int* rather than void*, it would be exactly the same at run time - but at compile time, you would be warned if you tried to set .pBits to point to anything but an int. A void* can be set to point to anything.

Remember that in C, a pointer is nothing but a runtime address - no type info, no size info. An array name is a pointer to the start of a memory area; the index is an offset from this start address (the index value must be multiplied with the element size to get the offset in bytes). Runtime info knows only of the start address, and nothing of index limits and element type. In memory, a 1-element DWORD array is identical to a single DWORD variable. It looks like an array because you write code to address memory locations with some offset.

If you ask the compiler to address something pointed to by .pBits, the compiler doesn't know what to find there. Do you want to fetch a single byte from memory? Or a DWORD? Maybe .pBits really is a pointer to a struct, and you want to address a struct member at a given offset (i.e. member name). You have to tell the compiler how to interpret the pointer. This is because you haven't declared it as e.g. a DWORD* but as a void*.

In your example, the programmer tells the compiler: "Treat .pBits as a DWORD*, a pointer to a double word!" Here, the pointer itself is copied to another pointer, which can be used to access the DWORD pointed to - that is just as a convenient shorthand notation. Whether following code uses the typed DWORD* 'pbits' or '(DWORD*)lockedrect.pBits' makes no difference (at least not until you want to change one of the two pointers without changing the other one).

I can't tell why the void* was cast to a DWORD*. My guess, from the name D3DLOCKED_RECT, is that .pBits points to a 3D coordinate, like a 3 element array (or maybe even an array of 3D points). The code you quote wants to manipulate the 3 values as a single unit (e.g for more efficient moving/copying). Why is a void* used, instead of a typed pointer? Probably because the struct can be used with different resolutions (maybe that is what is indicated by the .pitch member?): In some applications, the coordinates are represented by three 16 bit values, in other applications by three 32 bit values. In low-resolution applications, it could even be three 8-bit values. You cast it to whatever coordinate size you use.

The quoted code makes it look as if the coordinates could be three 64 bit values. I very much doubt that any graphical system would use 64 bit coordinates (unless you make 3D model of the known universe...). So probably the use of DWORD is just for efficiency, doing moving/copying of as few operations as possible. That you could probably find out reading the rest of the code where you found this line.
GeneralRe: void type Pin
CalinNegru(fearless_)11-Apr-20 10:25
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GeneralRe: void type Pin
Member 798912211-Apr-20 11:36
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GeneralRe: void type Pin
Richard MacCutchan11-Apr-20 23:40
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GeneralRe: void type Pin
Member 798912211-Apr-20 12:01
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GeneralRe: void type Pin
Greg Utas12-Apr-20 0:20
professionalGreg Utas12-Apr-20 0:20 
GeneralRe: void type Pin
leon de boer11-Apr-20 21:51
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GeneralRe: void type Pin
CalinNegru(fearless_)11-Apr-20 21:47
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QuestionHow do I add listboxes to a back buffer and use that? Pin
PotatoSoup6-Apr-20 5:57
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AnswerRe: How do I add listboxes to a back buffer and use that? Pin
Richard MacCutchan6-Apr-20 6:21
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GeneralRe: How do I add listboxes to a back buffer and use that? Pin
PotatoSoup6-Apr-20 6:46
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GeneralRe: How do I add listboxes to a back buffer and use that? Pin
Richard MacCutchan6-Apr-20 7:04
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GeneralRe: How do I add listboxes to a back buffer and use that? Pin
PotatoSoup6-Apr-20 7:26
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GeneralRe: How do I add listboxes to a back buffer and use that? Pin
Victor Nijegorodov6-Apr-20 8:24
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GeneralRe: How do I add listboxes to a back buffer and use that? Pin
PotatoSoup6-Apr-20 8:43
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GeneralRe: How do I add listboxes to a back buffer and use that? Pin
Victor Nijegorodov6-Apr-20 8:49
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GeneralRe: How do I add listboxes to a back buffer and use that? Pin
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GeneralRe: How do I add listboxes to a back buffer and use that? Pin
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