How to create UNION type like C Programer ?

[scila1996]

i Have a C Code

union
{
    int a;
    byte b;
} test_union;

int main
{
    test_union _var;
    _var.a = 256;
    _var.b = 2;
}

=> Result of _var.a => 258

I'm try with DllStructCreate with this way

Local $_union = DllStructCreate("byte[4]")
Local $_test_union = DllStructCreate("int a;int b", DllStructGetPtr($_union))
DllStructSetData($_test_union, 1, 256)
DllStructSetData($_test_union, 2, 2)
MsgBox(64, "", DllStructGetData($_test_union, "a"))

=> result is : 256 ?

 

How do i create a union with data organize like C ? Please help me ! Thank you for reply 

[jchd]

You're playing with firearms here: $_test_union is twice as large as $_union.

Anyway, this is the counterpart of your C example:

Local $_union = DllStructCreate("byte[4]")
Local $_test_union = DllStructCreate("int a", DllStructGetPtr($_union))
DllStructSetData($_test_union, 1, 256)
DllStructSetData($_union, 1, 2, 1)
MsgBox(64, "", DllStructGetData($_test_union, "a"))

 

[scila1996]

You're playing with firearms here: $_test_union is twice as large as $_union.

Anyway, this is the counterpart of your C example:

Local $_union = DllStructCreate("byte[4]")
Local $_test_union = DllStructCreate("int a", DllStructGetPtr($_union))
DllStructSetData($_test_union, 1, 256)
DllStructSetData($_union, 1, 2, 1)
MsgBox(64, "", DllStructGetData($_test_union, "a"))

 

How to get data of int b ?

[scila1996]

How to i create union with element is struct ? Example

typedef union _ULARGE_INTEGER {
  struct {
    DWORD LowPart;
    DWORD HighPart;
  };
  struct {
    DWORD LowPart;
    DWORD HighPart;
  } u;
  ULONGLONG QuadPart;
} ULARGE_INTEGER, *PULARGE_INTEGER;

 

Edited November 6, 2015 by scila1996

[jchd]

The struct u is pointless.

Simply like this:

Local $_union = DllStructCreate("long[2]")
Local $_test_union = DllStructCreate("int64 a", DllStructGetPtr($_union))
DllStructSetData($_union, 1, 0x12345678, 1)
DllStructSetData($_union, 1, 0x99999999, 2)
MsgBox(64, "", Hex(DllStructGetData($_union, 1, 1), 8))
MsgBox(64, "", Hex(DllStructGetData($_union, 1, 2), 8))
MsgBox(64, "", Hex(DllStructGetData($_test_union, "a"), 16))
MsgBox(64, "", DllStructGetData($_test_union, "a"))

 

[JohnOne]

How to get data of int b ?

I'm not 100% on this, but quite sure that you are missing the point of union.

I believe it's that it will be one variable stored in it, either the byte or the int, not both.

So because it can be an int, and an int is larger than byte, it has to at least the size of int.

Don't take that as definite, I've been known to be wrong.