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How to determint whether two DCOM files (DLL files) are the same or not?

Posted on 2009-03-31
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Hi Experts:

    I have a VB6 project producing a DLL file. I did the following experiment:
1. I open the VB6 project and compile it, then rename the resulted DLL file to Lib.DLL_1
2. compile again and rename the resulted DLL file to Lib.DLL_2
3. compare the files Lib.DLL_1 and Lib.DLL_2 with HEXCMP software(from http://www.grigsoft.com/hexcmp.htm)
4. I tried to compare these two files with MD5.exe, and the MD5 codes are different.

    Then the software show me that these two DLL files are different, while I expect them to be the same. Please help me at the following concerns:
1. Why would I get this result? Is it because of the time stamp of the files? or something else?
2. Can you suggest me a good way to compare the DCOM files?

More related information that I have: I have two files A and B with different names, and shown identical by HEXCMP and MD5.exe, so the file name should not matter. File B is obtained by moving A to a Visual Source Safe repository, and then retrive a copy from the repository. Then A and B are both renamed.

Thank you!
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Question by:huangs3
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cj_1969 earned 2000 total points
ID: 24039953
I'm no expert but reading this might help explain it ... http://en.wikipedia.org/wiki/MD5

Given that the hash is comprised of padded code, based on 128 bit segments then any optimization within the compile process that might change the order that the code is created and written out in not aonly CAN but WILL affect the hash code that is generated by the resultant file.

That said ... I don't know what is actually going on when you compile your code so this is purely hypothetical and just one idea/reason it would be producing different values.
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Author Closing Comment

by:huangs3
ID: 31565146
You point out a part that nobody except Microsoft programmer may know, and we cannot not tell anything without that
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