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How to transfer binary data form an ActiveX control ....

Posted on 2002-04-09
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Last Modified: 2013-11-20
I make a ActiveX control by "MFC ActiveX ControlWizard",now I want to transfer large numbers of binary data from ActiveX control to the caller.I do it like this:
ActiveX control source code:

BOOL CPctCtrl::MyTest(BSTR FAR* szOutBuffer, long nBufferLength)
{
     if(szOutBuffer == NULL)
     {
          return FALSE;
     }

     memcpy(szOutBuffer,"Test",sizeof("Test"));

     return TRUE;
}

I use Visual basic 6.0 to call this ActiveX control like this:

dim szOutBuffer(1024) as string
MyObject1.MyTest szOutBuffer(1),1024
end sub

when run the line "MyObject1.MyTest szOutBuffer(1),1024
" , the program will crashed with "invalid memroy address accessed!"

Cound help me to solve this problem?
Thanks in advance.
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Question by:gdzdongdong
  • 4
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8 Comments
 
LVL 3

Accepted Solution

by:
job_s earned 100 total points
ID: 6933494
I'm not an expert in VB
one doubt why ur calling szOutBuffer(1)

is szOutBuffer engough ??
MyObject1.MyTest szOutBuffer(1),1024

and why Ur using memcpy( ).
Allocate the BSTR by ::SysAllocStringByteLen( string, size );





BOOL CPctCtrl::MyTest(BSTR FAR* szOutBuffer, long nBufferLength)
{
    if(szOutBuffer == NULL)
    {
         return FALSE;
    }
    if( nBufferLength < strlen(test))
          return false; //buffer small to copy
    *szOutBuffer = ::SysAllocStringByteLen( "test", strlen(test));
    return TRUE;
}

0
 

Author Comment

by:gdzdongdong
ID: 6934022
Thank you for you answer,but my "szOutBuffer" is enough , because I just copy 10 bytes to "szOubBuffer", I think ,I'm in incorrect way ? Could any can help me ???
0
 
LVL 3

Expert Comment

by:job_s
ID: 6934079
If u want to follow ur current method U must add



memcpy(szOutBuffer,"Test",sizeof("Test"));

ZeroMemory( szOutBuffer, nBufferLength);
memcpy(szOutBuffer,"Test",strlen("test"));



try this


   

0
 
LVL 3

Expert Comment

by:job_s
ID: 6934497
I think the problem is because of missing the NULL char on the END of string.
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Author Comment

by:gdzdongdong
ID: 6935877
Thank yo job_b, but I already do it like this , memcpy(szOutBuffer,"test",sizeof("test")); but the program still crashed.... Help me???
0
 
LVL 3

Expert Comment

by:job_s
ID: 6936669
I think the problem is because of missing the NULL char on the END of string.
So use
ZeroMemory( szOutBuffer, nBufferLength);
memcpy(szOutBuffer,"Test",strlen("test"));
or use strcpy for copying string





0
 

Author Comment

by:gdzdongdong
ID: 6939439
Thanks everyone , I'll try it ...
0
 

Author Comment

by:gdzdongdong
ID: 6940118
I've tried all the way you have suggested , but the program still crashed ,,, how to do , everyone?
0

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