bool pointer from C++ to C#

Question

I want to use a function in a C++ DLL in my C# application using DLLImport:

BOOL IsEmpty( DWORD KeyID, BOOL *pFlag )

I tried many combinations but in vain, like:

public extern static bool IsEmpty(int KeyID, ref bool pFlag);

The method returns false (that means an error).

Any idea how to do that?

Minor note, `DWORD` is an unsigned 32-bit type. The corresponding type in C# is `uint`, not `int`. — cdhowie, Oct 03 '12 at 15:09
bool is the standard C++ type. BOOL is a MFC type. they are not the same. — Daniel Daranas, Oct 03 '12 at 15:11

score 4 · Answer 1 · edited May 23 '17 at 10:24

4

To quote "Willy" (with amendments):

Beware the booleans!

Win32 defines different versions of booleans.

1) BOOL used by most Win32 API's, is ~~an unsigned int~~ a signed int (4 bytes)

2) BOOLEAN is a single byte, only used by a few win32 API's!!

3) and C/C++ has it's builtin 'bool' which is a single byte

...and to add what @tenfour pointed out:

4) the even more bizarre VARIANT_BOOL

typedef short VARIANT_BOOL;
#define VARIANT_TRUE ((VARIANT_BOOL)-1)
#define VARIANT_FALSE ((VARIANT_BOOL)0)

The signed or unsigned nature shouldn't matter for BOOL, as the only "false" pattern is 0. So try treating it as a 4 byte quantity...however you interface with a DWORD may be satisfactory, (I've not dealt with Windows 64-bit conventions.)

edited May 23 '17 at 10:24

Community

1
1

answered Oct 03 '12 at 15:12

HostileFork says dont trust SE

32,904
11
98
167

I don't believe that the size of BOOL nor DWORD changes on 64-bit Windows. – cdhowie Oct 03 '12 at 15:15
1

I'd add the even more bizarre `VARIANT_BOOL` where `VARIANT_FALSE` is -1. – tenfour Oct 03 '12 at 15:20

score 1 · Answer 2 · answered Oct 03 '12 at 15:12

1

BOOL in Win32 is a typedef of int, so you should just change bool to Int32, so the definition is int IsEmpty(uint KeyID, ref int pFlag)

answered Oct 03 '12 at 15:12

BigBoss

6,904
2
23
38

score 1 · Answer 3 · answered Oct 03 '12 at 15:18

1

because in c++ BOOL is defined as int. You should use

    [return: System.Runtime.InteropServices.MarshalAsAttribute(System.Runtime.InteropServices.UnmanagedType.Bool)]
    public static extern  bool IsEmpty(uint KeyID, ref int pFlag) ;

answered Oct 03 '12 at 15:18

Manuel Amstutz

1,311
13
33

To be more precise: BOOL is defined inside the Win32 API header files (not any C++ standard, though C++ added a `bool` that did not exist in C). MSDN does however say it's a [signed int from WinDef.h](http://msdn.microsoft.com/en-us/library/windows/desktop/aa383751(v=vs.85).aspx)...not an unsigned as from the source I quoted. Although signed/unsigned technically should not matter as only 0 is FALSE and that has the same bit pattern regardless. :-/ – HostileFork says dont trust SE Oct 03 '12 at 15:40

score 0 · Accepted Answer · answered Oct 04 '12 at 07:58

0

Thank you for your help!

finally this works for me

public extern static int IsEmpty( int KeyID, int[] pFlag)

answered Oct 04 '12 at 07:58

user1717487

41
1
6

bool pointer from C++ to C#

4 Answers4