I'm looking for a C or C++ diff library. I know I can use the Unix diff tool in combination with system or exec, but I really want a library. It would be handy if the library could perform patches as well, like the Unix patch tool.
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Matt Fichman
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It seems to me that a diff library would be pretty common, but Google has yet to turn up a good answer. – Matt Fichman Sep 21 '09 at 19:28
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[An excellent approach was provided for C/C++ on a similar post.](https://stackoverflow.com/questions/42377443/diff-compare-two-files-by-file-descriptor-fd-instead-of-file-name/42380790#42380790) – Cloud Feb 22 '17 at 22:53
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I think I've found a good solution, finally:
The DTL - Diff Template Library --- Tutorial
It supports patch. I had to type "diff.cpp" into Google to find it. Hopefully it works!
maxschlepzig
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Matt Fichman
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It seems like the Google Diff, Match and Patch libraries are what you need.
Paul Biggar
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3Eh, but the C++ version of that library is dependent on Qt. I need a diff/patch library for a non-GUI application. – Matt Fichman Sep 20 '09 at 23:46
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13Qt is a large library dependency I don't want to have. Why didn't the author use STL? – Matt Fichman Sep 29 '09 at 20:48
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8An STL port [is available on GitHub](https://github.com/leutloff/diff-match-patch-cpp-stl). – Josh Kelley Oct 20 '14 at 20:19
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That's definitely better than DTL (which apparently does not offer a per-line diff algorithm) – jpo38 Nov 24 '16 at 20:29
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This is an implementation of a "solution to SES/LCS with the Hirschberg linear space refinement as described in the following publication":
E. Myers, ``An O(ND) Difference Algorithm and Its Variations,'' Algorithmica 1, 2 (1986), 251-266. http://www.cs.arizona.edu/people/gene/PAPERS/diff.ps
Found it on the Wikipedia page on diff.
That's only for finding a diff though, not applying it as a patch. I think that application of a patch is actually a harder problem; due to the risk of conflicts. It would need some form of user-controlling feedback mechanism, to resolve conflicts.
unwind
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This is the best I answer so far, but I really would like a patch library as well. I'll wait a little to see if anyone else has an answer. – Matt Fichman Sep 24 '09 at 16:48
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The file `diff.c` linked at the beginning appears to have disappeared. (It is still in the Google index though...) – Tanuva Jul 24 '17 at 09:02
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@unwind Oh my, I'm sorry. It is just the https transport that yields a 404 error. Disabling HTTPS Everywhere results in the file being loaded. – Tanuva Jul 24 '17 at 14:26
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There is one that is part of Mercurial. It exists as some C code that's designed as a Python extension, but it could probably be extracted pretty easily. I believe it can also do binary diffs.
The relevant .c files are mercurial/bdiff.c, mercurial/mpatch.c and possibly mercurial/diffhelpers.c.
Omnifarious
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Also pretty much unfindable in Google, it turns out that Gnulib has a diff module. This one seems sufficient for what I wanted a diff library for. It doesn't seem to have a patch module, though.
ptomato
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