| Re: HOW CAN I CALL AN EXTERNAL C ROUTINE FROM IDL ??? [message #20499] |
Thu, 29 June 2000 00:00 |
Steve Hartmann
Messages: 21
Registered: March 2000
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Junior Member |
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Terenzio Pucci wrote:
> I tried also examples that are contained in the
> "rsi\idl52\external\call_external\c" directory, but they don't work.
> They refer to a file call_library.dll that doesn't exist.
> "Call_library.def" and "Call_library.opt" only exist.
> Then i tried to build a dll, compiling one of the examples, under
> visual c++ 5.0.
>
xxx - Some example code removed - xxx
>
>
> CAN ANYONE HELP ME ???
>
> I NEED AN ILLUSTRATED EXAMPLE.
>
> THANKS
I agree that the documentation on this is not very complete. I spent quite a
bit of time trying to get this to work, but now I find it really easy to add
new functions when I need them. To help myself and others in our lab, I
created a small 'how to' document explaining how to create a DLL using MS
Visual C++ that can be called from IDL using Call_External. This works for
my Windows NT machine, but I think the procedure for a Mac is very similar.
I hope this helps,
Steve Hartmann
------------------------------------
How to create a Windows NT DLL for use with IDL's Call_External:
------------------------------------------------------------ ---
1. Create a Win32 DLL project using VC++.
2. Create desired member functions for this project.
a. It must have a DLLMain function.
3. The DLL must also include one of two additional items.
a. A .DEF file listing the DLL name and export member functions, OR
b. Member function defined using the _declspec(dllexport) command.
4. Compile and Link the project to create the DLL.
5. Use this DLL with Call_External.
------------------------------------------------------------ -------------
METHOD#1 -- Including a .def file in the project.
Here is an example of a .def file (include this with the project):
LIBRARY FunctionName
DESCRIPTION 'Optional description of function'
CODE PRELOAD MOVEABLE DISCARDABLE {Optional}
DATA PRELOAD MOVEABLE SINGLE {Optional}
EXPORTS MemberFunction1 @1
MemberFunction2 @2
MemberFunction3 @3
MemberFunction4 @4
Note: the @number field is optional and denotes the ordinal value.
Member functions are called as in method #2, without the DLLExport keyword.
------------------------------------------------------------ -------------
METHOD#2 -- Define member functions using _declspec(dllexport)
Here is an example of the header file definition of the member functions:
//myDLL.h
//Define a pointer to a float type.
#ifndef LPFLOAT
#define LPFLOAT FLOAT FAR*
#endif
#define DllExport _declspec(dllexport)
//Function prototypes.
BOOL WINAPI DllMain(HINSTANCE hInst, ULONG ulReason, LPVOID lpReserved);
long DllExport MemberFunction1(LONG lArgc, LPVOID lpvArgv);
long DllExport MemberFunction2(LONG lArgc, LPVOID lpvArgv);
int DllExport MemberFunction3(LONG lArgc, LPVOID lpvArgv);
LPSTR DllExport MemberFunction4(LONG lArgc, LPVOID lpvArgv);
--------------------------------------
Here are examples of the member functions included in myDLL.c:
1. Example 1
LONG DllExport MemberFunction1(LONG lArgc, LPVOID lpvArgv)
{
MessageBox(NULL, (LPSTR)"The call to TestOne() was successful.",
(LPSTR)"Reply From dlltst32.dll", MB_OK | MB_ICONINFORMATION);
return(1);
}
--------------------------------------
2. Example 2
LONG DllExport MemberFunction2(LONG lArgc, LPVOID lpvArgv)
{
LPLONG lplArray = NULL;
LPLONG* lplplArgv = NULL;
LONG lLen = 0;
LONG lSum = 0;
CHAR szMsg[256];
lplplArgv = (LPLONG*)lpvArgv;
lplArray = lplplArgv[0];
lLen = *lplplArgv[1];
// Determine the sum of the array elements.
while (lLen-- > 0) {
lSum += *lplArray++;
}
return(lSum);
}
------------------------------------------------------------ -----------
Both methods require a DllMain function in the DLL, similar to this:
#include "myDLL.h"
//Windows DLL entry point.
BOOL WINAPI DllMain(HINSTANCE hInst, ULONG ulReason, LPVOID lpReserved)
{
return(TRUE);
}
------------------------------------------------------------ -----------
------------------------------------------------------------ -----------
How to use the DLL in IDL:
1. Call without passing parameters:
lResult = CALL_EXTERNAL('myDLL.dll', 'MemberFunction1')
2. Call and pass a LONG array by reference, and a LONG scalar by reference.
lResult = CALL_EXTERNAL('myDLL.dll', 'MemberFunction2', LINDGEN(x), xL)
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