calling a shared lib from VBA in Excel

[Ian Kennedy]

Hi I'm attempting to call a function in a shared library from a VBA
macro in excel. This is a typical c function:

extern "C" bool SetBootstraps(int nBootstraps)

In VBA I have it declared as:

declare function SetBootstraps lib "mylib" (nBootstraps as long) as
Boolean

When I attempt to run this via the c debugger I don't get the value
passed down to excel that I would expect. What do I have to do to pass
variables down correctly. Do I need to use CDecl in the VBA or do I need
to use pascal in the C. Which is correct.

Also am I correct in thinking that the following is correct

VBA C
Integer short
Long int
Double double
Boolean bool

Thanks
Ian

 

[Chip Pearson]

Ian,

The C DLL function must have been compiled with the "__stdcall" modifier,
and the function must have been exported with a DEF file. Also, since the
SetBootstraps function requires a value of nBootstraps, not a pointer, you
need the ByVal modifier in your Declare statement.

Declare Function SetBootstraps lib "mylib" (ByVal nBootstraps As Long) As
Boolean


--
Cordially,
Chip Pearson
Microsoft MVP - Excel
Pearson Software Consulting, LLC
www.cpearson.com
(email address is on the web site)

 

[Chip Pearson]

Declare Function SetBootstraps lib "mylib" (ByVal nBootstraps As Long) As
Boolean

Should be

Declare Function SetBootstraps lib "mylib" (ByVal nBootstraps As Long) As
Long

Also, in VC++, there is "BOOL" and "bool", two distinct types: "BOOL" is a
long int (32-bits) and "bool" is a char (8-bits).

You can test the difference with

int __stdcall SizeOfBOOLUpperCase()
{
return sizeof(BOOL);
}

int _stdcall SizeOfboolLowerCase()
{
return sizeof(bool);
}

SizeOfBOOLUpperCase returns 4.
SizeOfboolLowerCase returns 1.


--
Cordially,
Chip Pearson
Microsoft MVP - Excel
Pearson Software Consulting, LLC
www.cpearson.com
(email address is on the web site)

 

[Ian Kennedy]

Ian,

The C DLL function must have been compiled with the "__stdcall" modifier,
and the function must have been exported with a DEF file. Also, since the
SetBootstraps function requires a value of nBootstraps, not a pointer, you
need the ByVal modifier in your Declare statement.

Thanks. I did have the ByVal in there I had forgotten to add it to by
post. The problem I have is that I am on a Mac.

What is the __stdcall equivilent on CodeWarrior, code warrior complains
at this structure. I have exported the function into my shared lib and
made it visible to the outside world. I can call into it but get junk
arguments passed down.

Declare Function SetBootstraps lib "mylib" (ByVal nBootstraps As Long) As
Boolean

Thanks
Ian

 

[Ian Kennedy]

Should be

Declare Function SetBootstraps lib "mylib" (ByVal nBootstraps As Long) As
Long

Also, in VC++, there is "BOOL" and "bool", two distinct types: "BOOL" is a
long int (32-bits) and "bool" is a char (8-bits).

I'm not on windows, so BOOL is probably not available. What is Excel VBA
expecting for a boolean return value? It seems to be 16 bit so I could
just use a 'short'.

You can test the difference with

int __stdcall SizeOfBOOLUpperCase()
{
return sizeof(BOOL);
}

int _stdcall SizeOfboolLowerCase()
{
return sizeof(bool);
}

SizeOfBOOLUpperCase returns 4.
SizeOfboolLowerCase returns 1.

Thanks again
Ian

 

[Chip Pearson]

Ian,

The safest bet in to check with your compiler documentation to see exactly
how it defines "bool". In older version of MS VC, 'bool' was defined the
same size as 'int'. In version 4.2, it was changed to a single char.

Additionally, you could write a simple "Hello, World" program to display the
length of "bool" and use a compatible variable type in VBA. E.g,

long int SizeOfbool()
{
printf("Size Of 'bool' in bytes: %d", sizeof(bool));
return sizeof(bool);
}

If bool is a single byte, use the VBA Byte data type. E.g.,

Public Declare Function ReturnboolLC Lib "TestDLL.dll" () As Byte

Sub AAA()
Dim L As Long ' can be any integral variable type. VBA will convert.
L = ReturnboolLC()
Debug.Print CStr(L)
End Sub

The _stdcall calling convention is a Microsoft-specific option in C. It
isn't supported in ANSI C. Therefore, if you want to call functions in C DLL
from VB/VBA, you need to write non-ANSI C code. If you need to keep your
procedures ANSI-compatible, you'll need to write an additional DLL that
wraps your ANSI functions up in _stdcall functions and compile that DLL in
VC++. You can read more about __stdcall at

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vclang/html/_core___stdcall.asp



--
Cordially,
Chip Pearson
Microsoft MVP - Excel
Pearson Software Consulting, LLC
www.cpearson.com
(email address is on the web site)

 

[Ian Kennedy]

Ian,

The safest bet in to check with your compiler documentation to see exactly
how it defines "bool". In older version of MS VC, 'bool' was defined the
same size as 'int'. In version 4.2, it was changed to a single char.

Additionally, you could write a simple "Hello, World" program to display the
length of "bool" and use a compatible variable type in VBA. E.g,

long int SizeOfbool()
{
printf("Size Of 'bool' in bytes: %d", sizeof(bool));
return sizeof(bool);
}

If bool is a single byte, use the VBA Byte data type. E.g.,

Public Declare Function ReturnboolLC Lib "TestDLL.dll" () As Byte

Sub AAA()
Dim L As Long ' can be any integral variable type. VBA will convert.
L = ReturnboolLC()
Debug.Print CStr(L)
End Sub

Sorry, you have be backwards, I was asking what Excel VBA used for the
size of Boolean, I will then match my C to that.

The _stdcall calling convention is a Microsoft-specific option in C. It
isn't supported in ANSI C. Therefore, if you want to call functions in C DLL
from VB/VBA, you need to write non-ANSI C code. If you need to keep your
procedures ANSI-compatible, you'll need to write an additional DLL that
wraps your ANSI functions up in _stdcall functions and compile that DLL in
VC++. You can read more about __stdcall at

Sorry, but I'm on a Macintosh, VC++ and DLLs have nothing to do with it.
Do you know what the calling convention should be for a Mac version of
Excel VBA? CodeWarrior on the Mac dose not have __stdcall so Excel can't
be using that, what does it use.
Thanks
Ian

 

[Chip Pearson]

Sorry, you have be backwards, I was asking what Excel VBA used for the
size of Boolean, I will then match my C to that.

I do have it backwards. Sorry about that. In VBA, a Boolean is a 2-byte
Integer.

Sorry, but I'm on a Macintosh, VC++ and DLLs have nothing to do with it.

You should said that initially. It makes a big difference. I wouldn't have
wasted my time. Macs make up a very small part of the universe, so I assumed
you were on a Windows machine.

You can use

Sub AAA()
Dim B As Boolean
Debug.Print LenB(B)
End Sub

to see how many bytes are occupied by Boolean.

I have no idea how things work on Mac. You might ask in one the dedicated
Mac Office newsgroups.



--
Cordially,
Chip Pearson
Microsoft MVP - Excel
Pearson Software Consulting, LLC
www.cpearson.com
(email address is on the web site)

 

[Ian Kennedy]

I do have it backwards. Sorry about that. In VBA, a Boolean is a 2-byte
Integer.


You should said that initially. It makes a big difference. I wouldn't have
wasted my time. Macs make up a very small part of the universe, so I assumed
you were on a Windows machine.

Appologies, I thought I had but looking back I see that I didn't.

You can use

Sub AAA()
Dim B As Boolean
Debug.Print LenB(B)
End Sub

to see how many bytes are occupied by Boolean.

I have no idea how things work on Mac. You might ask in one the dedicated
Mac Office newsgroups.

I have but today I have had no response. The trouble with an Excel Mac
newsgroup is that this is really a programming question to do with
Excel. This would seem to be the correct group, perhaps it should be
renamed to include windows.

Thanks for you time
Ian