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How to call a function present in a COM based DLL

I want to use a COM component known as DigiSign. Following is an extract of the help file.

About DigiSign 2.0
DigiSign implements the most popular message digest and checksum algorithms: SHA-1, SHA-256, SHA-384, SHA-512, MD5, MD2, RIPEMD160, CRC32 and ADLER32.

DigiSign can be used with any COM compliant environment: Scripting languages (VBScript, JavaScript), Visual Basic (Versions 4 and up), VBA (Word, Excel, Access ...), VC++, BC++, Delphi, Power Builder.

The VB Example that is given is as follows:

'DigiSign 2.0 VBScript Sample
'Create Hash Object
Set H = CreateObject ("DigiSign.Hash")

'Calculate the MD5 Signature of a string
S = H.CalculateStringDigest("This is our test string", 4)

MY QUESTION is how do we do the same in C++/VC++

Please note:
1. GUID is not provided
2. No .h files are provided
3. The above code works properly in VB
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1 Solution
I would recommend importing the file that contains the object.  Running a generic compile after importing should generate a tlh (?? i might be wrong) file which contains most of the prototypes etc.  I used

#import "C:\Program Files\Donia Software\Digisign 2.0\Digisign.dll"

void main(void)


and a TLH file was generated in the debug directory when i compiled this. From that I was able to derive the class names, the members and the methods.  

#import "C:\Program Files\Donia Software\Digisign 2.0\Digisign.dll" no_namespace

void main(void)
     IHashPtr test;


Hope this helps.
reacharunAuthor Commented:
Following is the dump of errors I got after doing what you specified

--------------------Configuration: testDigi - Win32 Debug--------------------
E:\workarea\msdev\testDigi\testDigi.cpp(7) : error C2065: 'IHashPtr' : undeclared identifier
E:\workarea\msdev\testDigi\testDigi.cpp(7) : error C2146: syntax error : missing ';' before identifier 'test'
E:\workarea\msdev\testDigi\testDigi.cpp(7) : error C2065: 'test' : undeclared identifier
E:\workarea\msdev\testDigi\testDigi.cpp(8) : error C2228: left of '.CreateInstance' must have class/struct/union type
E:\workarea\msdev\testDigi\testDigi.cpp(10) : error C2227: left of '->About' must point to class/struct/union
Error executing cl.exe.

testDigi.obj - 5 error(s), 0 warning(s)
Is the precompiler #import directive pointing to the correct location of the digisign DLL? I used the default installation directory.  Also, check the TLH file and ensure that the IHash object exists. Hope this will help.
No comment has been added lately, so it's time to clean up this TA. I will
leave a recommendation in the Cleanup topic area that this question is:

Answered: Points to mmurrell: Grade A

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