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In the whodunit assignment, when I used the copy.c given in the pset4.zip on smiley.bmp and executed the diff check, there was no message shown. However, when I used the copy.c and diff on the clue.bmp, it gave me the message "Binary files clue.bmp and verdict.bmp differ." Could someone tell me what I'm doing wrong?

Thanks so much

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  • so you created a copy from clue.bmp and named it verdict.bmp using copy and diff says the two copies are different?
    – kzidane
    Jul 4 '15 at 4:42
  • yep, but I see they are both 922KB Jul 4 '15 at 4:45
  • having the same size doesn't necessarily mean that the data is the same. did you by any chance modify copy.c and recompiled the program?
    – kzidane
    Jul 4 '15 at 4:55
  • nope i didn't modify copy.c Jul 4 '15 at 4:58
  • yeah actually diff doesn't say two files are different unless they truly are. so just to be absolutely sure about what you did, did you execute ./copy clue.bmp verdict.bmp then diff clue.bmp verdict.bmp and diff said they were different?
    – kzidane
    Jul 4 '15 at 5:02
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I just checked and apparently this is the answer. that is, the program that was used to create clue.bmp added 2 bytes at the end of the file. copy.c does not assume there are any additional bytes other than the BMP itself (i.e., the headers and the image).

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