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#1234 WinMerge fails comparing two large files (>500m)


I am comparing two copies of
WINDOWS_SERVER_2003_R2_ENT.iso wich is about 566m in
size. WinMerge 2.4.6 fails and says that there was an
error without further details.


  • Kimmo Varis
    Kimmo Varis

    Logged In: YES

    WinMerge cannot open such big files to file compare. And it
    cannot open binary files anyway. Folder compare can compare
    big files and show if they are identical or different.

  • Neo

    Logged In: YES

    So you have already that function but however that function
    is not hooked into FILE compare? That's strange...

  • Kimmo Varis
    Kimmo Varis

    Logged In: YES

    Not strange at all. Targets for file and folder compare are
    totally different. For folder compare we only need info if
    files are identical or different. For file compare we need
    exact list of differences inside files.

    So for folder compare it is enough we found one difference
    from files. We don't need anything else. So we don't even
    need to try to look for exact differences. (That is what
    different compare methods are for: content compare looks for
    exact differences, quick compare just looks for one difference).

    So for file compare we always have to try to get exact
    differences, otherwise there is no point in merging. This
    error situation you reported is not easy to solve. We should
    somehow know beforehand we can't get exact differences from
    file (too large, binary file, situations like that) and
    switch to simpler mode.

    We could of course do compare with simple method after exact
    differences method fails. But if files are like in your
    case, Gigabyte, it would take considerable time.

  • Logged In: NO

    So why not just use the function in folder compare? It 2
    files are different, just display 'different'; if they are
    identical, display 'identical'. That's enough. I don't
    expect you to display the differences for such big files
    (>50m). Anyway, I can use UltraEdit's free compare to
    compare binary files safely, even for these large files.

  • Kimmo Varis
    Kimmo Varis

    Logged In: YES

    Problem is need for multiple compares for files which may
    take a lot of time.

    We cannot know before comparing if the file is binary file
    or text file. So we must first compare it as a text file. If
    that fails then we could compare it again as a binary file...

    And before somebody suggests it: we cannot use filename
    extension. It is not reliable in Windows. For example you
    can have file.doc file which could be just simple text file
    or MS Word document file.

  • Kimmo Varis
    Kimmo Varis

    • milestone: --> Branch_+_Trunk
    • priority: 5 --> 3
  • Ian Ward
    Ian Ward

    Logged In: YES
    Originator: NO

    WinMerge fails comparing large text files also (the files in question being log 2.5 MB each). It shows differences in the beginning of the file (up to about 5000 lines into the file), but does not show any of the later portions of the file. I do this regularly and so have had to use a different differencing program to compare them.