DLL String Pointer Question

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Hi Markus,

> I've forgotten one thing:
>
> > a *CSTRING requires eight bytes.
>
> What ist the format of *CSTRING? 4 bytes pointer + 4 bytes length?

It's some kind of "hidden" pointer to an appropriate amount of memory. It
pushes a hidden argument on the stack, which is a pointer to a temporary
buffer (located on the stack). The called function itself then copies the
return value to this buffer.

Friedrich

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Is this clarion specific?

Or can you give me a "real world" example, when I should use *CSTRING?

Markus

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Hi Markus,

> Is this clarion specific?
>
> Or can you give me a "real world" example, when I should use *CSTRING?

If you make use of Windows APIs or DLLs written in Visual Studio C/C++ then
you would not use the *CSTRING type. You would use *STRING in this case.

To be honest, I don't know if this is Clarion specific. But we need this
type if we call a Clarion DLL.

Friedrich

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Thank you.

Markus

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Hi Friedrich,

here are the important sentences of our conversation. It would be nice,
if you could add this to the documentation:

String Encoding
The "Call Dll" script function makes use of the ANSI string encoding.

Result Type
The internal return types in the underlying Call Dll methoda are an
union of standard types, ranging from a four-byte INT (generic four-byte
type) to an eight-byte DOUBLE. %_SB_RETURN% itself is "typeless". SB
script variables are always represented as String and SB do the
conversion on the fly, if it is needed for arithmetics or call dll and
so on.

*STRING and *CSTRING
The difference between *CSTRING and *STRING is that the byte width of
the individual function arguments is different (64 bit for *CSTRING and
32 bit for *STRING). In the Call DLL method, it always allocates 10,240
bytes. All the parameters are pushed directly onto the stack. If the
called function (e.g. GetUserName) returns then it copies the retrieved
return value via lstrcpy() to the "final" variable location (e.g.
%STRINGBUFFER%). This variable is dynamically allocated (using
lstrlen). Everything you have after the null terminating character is
"ignored" in this final step. We adjust the stack and read the return
value(s). If the return value isn't passed through registers, memory
copy is performed instead.

What ist the format of *CSTRING?
It's some kind of "hidden" pointer to an appropriate amount of memory. It
pushes a hidden argument on the stack, which is a pointer to a temporary
buffer (located on the stack). The called function itself then copies the
return value to this buffer.

When should I use *CSTRING and when *STRING?
If you make use of Windows APIs or DLLs written in Visual Studio C/C++
then you would use the *STRING type. If you call a Clarion DLL, use
*CSTRING.


Markus

[NewsArchive]

Hi Friedrich,

this seems not to be added to the coumentation in 7.2.3062

Markus

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Hi Markus,

>
> this seems not to be added to the coumentation in 7.2.3062
>

I don't know if there were plans to add this to the documentation. But I'll
check this.

Thanks,
Friedrich

[NewsArchive]

Added as a FAQ topic to the "Call DLL Function" description now.

Thanks,
Friedrich

[NewsArchive]

Thank you.

Markus Zander