oicompare

oicompare is a very simple program for comparing files. It works both as a command line utility and as a library, for example for embedding in custom checker programs. Tested on 1300 submissions with 80k tests, it's faster than old compare. It's used in OIOIOI when no custom checker is provided.

Building

oicompare has very minimal dependencies:

• A C++20 compatible compiler (tested on recent GCC and Clang)
• The Meson build system (so also the Ninja build tool)

oicompare also uses two libraries internally, but these are both embedded and there is no extra effort in getting them:

• fmt for message formatting
• mio for memory mapped files

Command line usage

To use the oicompare program, simply pass it two files:

oicompare expected.txt received.txt

You may also pass the third argument to select a different translation:

oicompare expected.txt received.txt english_terse

Please note that most translations will assume that the first file is the expected program output and the second file is the got program output. Specify the translation in the form language_kind.

The following languages are available:

• english (the default) – messages in English
• polish – messages in Polish

The following translation kinds are available:

• terse – only print whether the inputs match, this yields no more information than the exit code
• abbreviated – show the mismatched tokens, using no more than 100 bytes for each token's representation, and thus no more than 255 bytes for the entire report
• full – show the mismatched tokens

API usage

The header-only API in oicompare.hh provides the oicompare::compare function (in two variants), along with supporting types oicompare::token_type, oicompare::token<It> and oicompare::mismatch<It1, It2>.

The oicompare::compare function accepts either two forward ranges of char, or two iterator-sentinel pairs. This means that memory-mapped files and strings are easily comparable. However, to use this on sequential file streams (for example, for pipes), you would need to implement a buffer with unlimited look-back.

The result is optional<mismatch<It1, It2>>, with mismatch specialized for iterators of the two ranges passed (they need not be of the same type). An empty value means that no mismatch was found (so the inputs are equivalent). The mismatch structure has the following fields:

enum class token_type
{
  word,
  newline,
  eof
};

template <typename It>
struct token
{
  token_type type;
  It first;
  It last;
};

template <typename It1, typename It2>
struct mismatch
{
  make_unsigned_t<iter_difference_t<It1>> line_number;
  optional<pair<It1, It2>> first_difference;
  token<It1> first;
  token<It2> second;
};

Where first and second are the tokens from the first and second file respectively that differ.

Tests

Test data is encoded in tests.hh. The file tester.cc runs these tests both during compile time (as all of oicompare logic is constexpr) and during run time. The tester is primitive and may be expanded in the future. The API of the test data is currently not stable.