Scnlib Files

Breaking changes

• The default behavior for scanning integers is now d (decimal) instead of i (detect base from prefix).

  :::cpp // v3 auto result = scn::scan<int>("077", "{}"); // result->value() == 77 result = scn::scan<int>("078", "{}"); // result->value() == 78

  // v2 auto result = scn::scan<int>("077", "{}"); // result->value() == 63 result = scn::scan<int>("078", "{}"); // result->value() == 7 // result->range() == "8" // (Because of the '0' prefix, an octal number is expected, // and '8' is not a valid octal digit, so reading is stopped)

• A large part of the bundled <ranges>-implementation is removed. Only the parts strictly needed for the library are included.

• The library no longer uses a stdlib provided <ranges>, even if available.
• This cut down compile times massively for library consumers

• You now may need to specialize scn::ranges::enable_borrowed_range for your own range types, even if you've already specialized std::ranges::enable_borrowed_range. Specializations of std::basic_string_view are already borrowed out of the box.

  :::cpp // std::span is a borrowed_range, // but scnlib doesn't know about it auto result = scn::scan<...>(std::span{...}, ...); // decltype(result->range()) is scn::ranges::dangling

  namespace scn::ranges { template <typename T, size_t E> inline constexpr bool enable_borrowed_range<std::span\<T, E>> = true; }

  auto result = scn::scan<...>(std::span{...}, ...); // decltype(result->range()) is a scn::ranges::subrange<const T*>

• scn::span is removed

• scan_arg_store and borrowed_subrange_with_sentinel are removed from the public interface
• scan_arg_store is changed to be non-copyable and non-movable, for correctness reasons (it holds references to itself, copying and moving would be needlessly expensive)

• The interface of make_scan_result is changed to take a tuple instead of the now unmovable scan_arg_store.

  :::cpp // v3 auto args = make_scan_args<scan_context, Args...>(); auto result = vscan(source, format, args); return make_scan_result(std::move(result), std::move(args.args()));

  // v2 auto args = make_scan_args<scan_context, Args...>(); auto result = vscan(source, format, args); return make_scan_result(std::move(result), std::move(args));

• The meaning of the "width" field in format specifiers is changed to mean the minimum field width (like in std::format), instead of the maximum (sort of like in scanf)

  :::cpp // v3 auto result = std::scan<int>("123", "{:2}"); // result->value() == 123 // result->range() == ""

  // v2 auto result = std::scan<int>("123", "{:2}"); // result->value() == 12 // result->range() == "3"

Features

• The "precision" field is added as a format specifier, which specifies the maximum fields width to scan (like in std::format)

  :::cpp // Scan up to 2 width units auto result = scn::scan<int>("123", "{:.2}"); // result->value() == 12 // result->range() == "3"

• Support for field fill and alignment is added. This interacts well with the new width and precision fields

  :::cpp // Read an integer, aligned to the right ('>'), with asterisks ('') auto result = std::scan<int>("*42", "{:>}"); // result->value() == 42 // result->range() == ""

  // Read an integer, aligned to the left ('<'), with whitespace (default), // with a maximum total width of 3 auto result = std::scan<int>("42 ", "{:<.3}"); // result->value() == 42 // result->range() == " "

• In general, there seems to be a ~10% to 20% improvement in run-time performance.

Changes

• The dependency on simdutf is removed. The library now has no external dependencies to compiled libraries (FastFloat, an internal dependency, is a header-only library)
• The number of source files is dramatically decreased: there are now just the public headers, a private implementation header, and a private implementation source file. This cuts down the time needed to compile the library, and any user code including it to a half (yes, really!)

Fixes

• Fix skipping of multiple characters of whitespace in the format string (reported in [#116], thanks @Jonathan-Greve (Jonathan Bjørn Greve))

Full Changelog: https://github.com/eliaskosunen/scnlib/compare/v2.0.3...v3.0.0