Niels Lohmann
abbe52d6de
* docs: qualify the operator>> stream positioning guarantee operator>>'s notes state that it leaves the stream positioned right after the parsed value, so that concatenated JSON values can be read back to back. That does not hold when the value is a number: a number is only terminated by the character that follows it, and the lexer's unget() is simulated (it rewinds only the lexer's own bookkeeping), so that character stays consumed from the stream. Document the actual behaviour: the guarantee holds for all value types except numbers, which must be followed by whitespace. Also qualify the cross-reference on the JSON Lines page, which repeated the unqualified claim. Documentation only; the behaviour itself is tracked in #5340. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * fix: restore the character that terminates a number (#5340) operator>> is documented to leave the stream positioned right after the parsed value, so that concatenated JSON values can be read back to back. That did not hold for numbers: a number is only terminated by the character following it, and lexer::scan_number() reads that character and calls unget() -- which is simulated and rewinds only the lexer's own bookkeeping. input_stream_adapter consumes via sbumpc() with no matching sungetc(), so the terminating character stayed consumed and the next extraction started one byte too late ('1true' left the stream at 'rue'). Propagating unget() to the adapter directly does not work: next_unget makes the following get() replay the cached character, so the terminator would be delivered twice. Instead, restore the still-pending character once at the end of a non-strict parse, where the input is handed back to the caller: - input_stream_adapter gains unget_character() (sungetc()) and advertises it via supports_unget, detected the same way as supports_seek. - lexer::restore_pending_unget() turns a pending simulated unget of a real (non-EOF) character into a real one and clears next_unget so the character is not also replayed. It is a no-op for adapters that cannot unget, and reports failure when sungetc() fails, in which case the input is left as it was before. - parser calls it on the three non-strict paths, i.e. for operator>> and sax_parse(strict = false). Strict parse()/accept() are unaffected: they require the input to end after the value, so the character is consumed by the end-of-input check anyway. Parse error messages and reported positions are unchanged. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * tests: fix CI failures in the #5340 test helpers Four CI failures, all in the new test code: - GCC (-Werror=useless-cast): drop the `json(...)` wrapper around `json::parse(...)`, which already returns a `json`. - GCC (-Werror=unused-result): assign the discarded `json::parse()` result to a dummy, the idiom used elsewhere in the test suite, and catch `json::parse_error&` for consistency. - clang-tidy (google-default-arguments): remove the default argument from the `pbackfail()` override; `sungetc()` supplies the base declaration's default. - MSVC (bad allocation): `no_putback_streambuf::underflow()` set a one-character get area without advancing `m_pos`, so an implementation whose `istream::get` peeks before it bumps re-read the same character forever. Keep no get area at all: `underflow()` peeks, `uflow()` consumes, and `sungetc()` still always lands in `pbackfail()`, which is what the test needs. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * fix: leave the character that terminates a number in the input Read the character following a number without consuming it, instead of consuming it and putting it back. input_stream_adapter now peeks with sgetc() and only steps over the character when the next one is requested or when the adapter is destroyed, so releasing it cannot fail - no putback position is required from the streambuf. Suggested by gregmarr in #5344. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * docs: match the version history wording to the peek-based fix Signed-off-by: Niels Lohmann <mail@nlohmann.me> * docs: drop the whitespace-separator caveat from the parsing pages The caveat added in #5343 describes the behavior this branch fixes: a number no longer consumes the character that terminates it, so concatenated values need no separator. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * refactor: split the strict and non-strict paths in parser Folding the release_lookahead() call into the existing strict check left the "in strict mode" comment on an else-if branch, and made the strict condition in sax_parse() redundant with the branch it followed. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Put the stream position fix behind JSON_PRECISE_STREAM_POSITION Leaving the character that terminates a number in the stream is observable: reading "1,2,3" with repeated operator>> works today only because the comma after each number is swallowed, and std::getline after a number skips the line break. Both break with the fix, so make it opt-in for 3.x, as suggested by @gregmarr in the review. - JSON_PRECISE_STREAM_POSITION (default 0) selects the peek-based input_stream_adapter. Without it, the adapter is the consuming one from develop and has no supports_lookahead, so lexer::release_lookahead() and the parser's calls to it compile to nothing. - The macro changes input_stream_adapter's layout and member functions, so it gets the ABI tag _psp, after _bics. The ABI config tests, the natvis generator, and nlohmann_json.natvis (regenerated) know the tag. - The tests for the fix move to unit-precise-stream-position.cpp, which defines the macro itself and runs in every build, and gain the two cases above. unit-deserialization.cpp pins the default behavior instead. - The docs describe the default behavior again and point to the new macro page; version history says "added in 3.13.0, planned default in 4.0.0". Signed-off-by: Niels Lohmann <mail@nlohmann.me> --------- Signed-off-by: Niels Lohmann <mail@nlohmann.me>
7.4 KiB
Macros
Some aspects of the library can be configured by defining preprocessor macros before including the json.hpp
header. See also the macro overview page.
Runtime assertions
- JSON_ASSERT(x) - control behavior of runtime assertions
Exceptions
- JSON_CATCH_USER(exception)
JSON_THROW_USER(exception)
JSON_TRY_USER - control exceptions - JSON_DIAGNOSTICS - control extended diagnostics
- JSON_DIAGNOSTIC_POSITIONS - access positions of elements
- JSON_NOEXCEPTION - switch off exceptions
Parsing
- JSON_PRECISE_STREAM_POSITION - opt in to leaving an input stream positioned right after a parsed number
- JSON_STRICT_NUL_HANDLING - opt in to rejecting a NUL byte in the input instead of treating it as end of input
Language support
- JSON_HAS_CPP_11
JSON_HAS_CPP_14
JSON_HAS_CPP_17
JSON_HAS_CPP_20 - set supported C++ standard - JSON_HAS_FILESYSTEM
JSON_HAS_EXPERIMENTAL_FILESYSTEM - controlstd::filesystemsupport - JSON_HAS_RANGES - control
std::rangessupport - JSON_HAS_STD_FORMAT - control
std::format/std::formattersupport - JSON_HAS_THREE_WAY_COMPARISON - control 3-way comparison support
- JSON_NO_IO - switch off functions relying on certain C++ I/O headers
- JSON_NO_THREAD_LOCAL - switch off the use of
thread_localstorage - JSON_SKIP_UNSUPPORTED_COMPILER_CHECK - do not warn about unsupported compilers
- JSON_USE_GLOBAL_UDLS - place user-defined string literals (UDLs) into the global namespace
- JSON_USE_SIMDUTF - use the simdutf library to accelerate UTF-8 validation
Library version
- JSON_SKIP_LIBRARY_VERSION_CHECK - skip library version check
- NLOHMANN_JSON_VERSION_MAJOR
NLOHMANN_JSON_VERSION_MINOR
NLOHMANN_JSON_VERSION_PATCH - library version information
Library namespace
- NLOHMANN_JSON_NAMESPACE - full name of the
nlohmannnamespace - NLOHMANN_JSON_NAMESPACE_BEGIN
NLOHMANN_JSON_NAMESPACE_END - open and close the library namespace - NLOHMANN_JSON_NAMESPACE_NO_VERSION - disable the version component of the inline namespace
Type conversions
- JSON_BRACE_INIT_COPY_SEMANTICS - opt in to copy/move semantics for single-element brace initialization
- JSON_DISABLE_ENUM_SERIALIZATION - switch off default serialization/deserialization functions for enums
- JSON_USE_IMPLICIT_CONVERSIONS - control implicit conversions
Comparison behavior
- JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON - control comparison of discarded values
Serialization/deserialization macros
Enums
- NLOHMANN_JSON_SERIALIZE_ENUM - serialize/deserialize an enum
- NLOHMANN_JSON_SERIALIZE_ENUM_STRICT - serialize/deserialize an enum with exceptions
Classes and structs
-
NLOHMANN_DEFINE_TYPE_INTRUSIVE - serialize/deserialize a non-derived class with private members
-
NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT - serialize/deserialize a non-derived class with private members; uses default values
-
NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE - serialize a non-derived class with private members
-
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE - serialize/deserialize a non-derived class
-
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT - serialize/deserialize a non-derived class; uses default values
-
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE - serialize a non-derived class
-
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE - serialize/deserialize a derived class with private members
-
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT - serialize/deserialize a derived class with private members; uses default values
-
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE - serialize a derived class with private members
-
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE - serialize/deserialize a derived class
-
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT - serialize/deserialize a derived class; uses default values
-
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE - serialize a derived class
-
NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_NAMES - serialize/deserialize a non-derived class with private members; uses custom names
-
NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES - serialize/deserialize a non-derived class with private members; uses default values; uses custom names
-
NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES - serialize a non-derived class with private members; uses custom names
-
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES - serialize/deserialize a non-derived class; uses custom names
-
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES - serialize/deserialize a non-derived class; uses default values; uses custom names
-
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES - serialize a non-derived class; uses custom names
-
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_NAMES - serialize/deserialize a derived class with private members; uses custom names
-
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES - serialize/deserialize a derived class with private members; uses default values; uses custom names
-
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES - serialize a derived class with private members; uses custom names
-
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_NAMES - serialize/deserialize a derived class; uses custom names
-
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES - serialize/deserialize a derived class; uses default values; uses custom names
-
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES - serialize a derived class; uses custom names