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• VB.Net Union Type (3-Feb-06 12:30)
  
• Union Types · Sorbet
  

union beispiel

{

  float preis;

  int anzahl;

} beispiel_fuer_zwei;

Declare Function xyz ( . . .ByVal lpString As Any) As Integer

(05-30-2024, 09:02 PM)Kernelpanic Wrote: A "union{}" is a mixed type in C. It is comparable to a *)"struct{}" in C with the difference that all variables share the same memory space; the memory space is determined by the compiler based on the longest variable.
*)A C-struct{} is comparable to Type ... End Type in Basic.
...
The "As Any" command in Visual Basic is used to remove the parameter type check when passing parameters. Simply put, it is a hint to the programmer that there is a type difference.

(05-30-2024, 09:55 PM)DSMan195276 Wrote: I'm pretty sure in this context the `ByRef pData As Any` is just their way of expressing the `void *` type in C. That itself more or less just means it's a pointer to data but the type of data is not specified. As far as QB64 is concerned, you'd just replace it with a ByVal _OFFSET.

KernelPanic explained the Union thing, I'd say in practice what you'll need to do in QB64 is use a memory buffer and copy the data into variables of the right kind based on the dwType entry, so a fair amount more annoying (since QB64 doesn't have actual unions to use). I'd probably just use `_MEMNEW()` to create a memory block of the right size and pass that in as `pData`. Then you can use `_MEMGET` to copy the union section into separate variables of the proper TYPE after checking the `dwType` value, and go from there.

(05-30-2024, 10:14 PM)SpriggsySpriggs Wrote: Check the code in that "GPT just rewrote my code" thread. The code there handles MEM for any type.

//union und struct Beispiel - 31. Mai 2024



#include <stdio.h>

#include <stdlib.h>



int main(void)

{

union uni_beispiel

{

int i_zahl;

float f_zahl;

char c_zeichen;

}u_beispiel;



struct stu_beispiel

{

int i_stzahl;

float f_stzahl;

char c_stzeichen;

}st_beispiel;



u_beispiel.i_zahl = 12;

printf("\nUnion-Zahl: %3d", u_beispiel.i_zahl);



u_beispiel.f_zahl = 44.15;

printf("\nUnion-Fliesskommazahl: %5.2f", u_beispiel.f_zahl);



u_beispiel.c_zeichen = 'A';

printf("\nUnion-Zeichen: %c", u_beispiel.c_zeichen);



//Anzeigen wieviel Speicher union und struct belegen

printf("\n\nGroesse im Speicher von struct: %3d Bytes", sizeof(struct stu_beispiel));

printf("\nGroesse im Speicher der union : %3d Bytes", sizeof(union uni_beispiel));



return(0);

}

Dim Shared Motorrad As MotorradModell

"Modell : ", Motorrad.Modell

(05-31-2024, 01:16 PM)Kernelpanic Wrote: An example of how unions and structures are used, and how much memory is used.

To explain again: In a union, the memory requirement is equal to the largest variable.
All variables in a union have to share this memory, so one have to know exactly which one one want to use.
In a structure, each variable gets its own memory space.

(05-30-2024, 09:55 PM)DSMan195276 Wrote: I'm pretty sure in this context the `ByRef pData As Any` is just their way of expressing the `void *` type in C. That itself more or less just means it's a pointer to data but the type of data is not specified. As far as QB64 is concerned, you'd just replace it with a ByVal _OFFSET.

KernelPanic explained the Union thing, I'd say in practice what you'll need to do in QB64 is use a memory buffer and copy the data into variables of the right kind based on the dwType entry, so a fair amount more annoying (since QB64 doesn't have actual unions to use). I'd probably just use `_MEMNEW()` to create a memory block of the right size and pass that in as `pData`. Then you can use `_MEMGET` to copy the union section into separate variables of the proper TYPE after checking the `dwType` value, and go from there.

(06-01-2024, 01:18 AM)DSMan195276 Wrote: I don't have tons of time at the moment, but to address a couple of the things you mentioned:

You're correct about the `_OFFSET` type. The member you identified (`hDevice`) is a `HANDLE` type which is the same size as a pointer.

Yes `ASCIIZ * 50` would be a 50 byte string, you'll need to check if the 50 includes the NUL byte at the end or not (if it does, then you can use `STRING * 50` for it, if the NUL byte is extra then it's a `STRING * 51`).

The ` bRawData[1]` thing is hard to explain, but basically it's a C concept where the size of the TYPE/struct is not really defined, instead there's an array of unknown length at the end of it. If you read the specs, it says that the size of the `bRawData` array is `dwSizeHid * dwCount`. I assume you then split the `bRawData` bytes up into `dwSizeHid`-sized chunks and each is a HID report or something.

Also, something to keep in mind is the C padding rules. Each type has a required alignment and the C compiler will insert empty space between the members of the struct to make sure each member hits its required alignment. QB64 does not do this, so you have to manually insert extra members for the padding. The majority of those structures are designed such that they don't need any padding, but maybe not all of them.