The Basics ========== An overview of what you need to know to use simdjson, with examples. * [Requirements](#requirements) * [Including simdjson](#including-simdjson) * [Using simdjson as a CMake dependency](#using-simdjson-as-a-cmake-dependency) * [The Basics: Loading and Parsing JSON Documents](#the-basics-loading-and-parsing-json-documents) * [Using the Parsed JSON](#using-the-parsed-json) * [C++11 Support and string_view](#c11-support-and-string_view) * [C++17 Support](#c17-support) * [Minifying JSON strings without parsing](#minifying-json-strings-without-parsing) * [UTF-8 validation (alone)](#utf-8-validation-alone) * [JSON Pointer](#json-pointer) * [Error Handling](#error-handling) * [Error Handling Example](#error-handling-example) * [Exceptions](#exceptions) * [Tree Walking and JSON Element Types](#tree-walking-and-json-element-types) * [Newline-Delimited JSON (ndjson) and JSON lines](#newline-delimited-json-ndjson-and-json-lines) * [Thread Safety](#thread-safety) * [Standard Compliance](#standard-compliance) Requirements ------------------ - A recent compiler (LLVM clang6 or better, GNU GCC 7.4 or better) on a 64-bit (ARM or x64 Intel/AMD) POSIX systems such as macOS, freeBSD or Linux. We require that the compiler supports the C++11 standard or better. - Visual Studio 2017 or better under 64-bit Windows. Users should target a 64-bit build (x64) instead of a 32-bit build (x86). We support the LLVM clang compiler under Visual Studio (clangcl) as well as as the regular Visual Studio compiler. We also support MinGW 64-bit under Windows. Including simdjson ------------------ To include simdjson, copy [simdjson.h](/singleheader/simdjson.h) and [simdjson.cpp](/singleheader/simdjson.cpp) into your project. Then include it in your project with: ```c++ #include "simdjson.h" using namespace simdjson; // optional ``` You can compile with: ``` c++ myproject.cpp simdjson.cpp ``` Note: - Users on macOS and other platforms were default compilers do not provide C++11 compliant by default should request it with the appropriate flag (e.g., `c++ -std=c++17 myproject.cpp simdjson.cpp`). - Visual Studio users should compile with the `_CRT_SECURE_NO_WARNINGS` flag to avoid warnings with respect to our use of standard C functions such as `fopen`. Using simdjson with package managers ------------------ You can install the simdjson library on your system or in your project using multiple package managers such as MSYS2, the conan package manager, vcpkg, brew, the apt package manager (debian-based Linux systems), the FreeBSD package manager (FreeBSD), and so on. [Visit our wiki for more details](https://github.com/simdjson/simdjson/wiki/Installing-simdjson-with-a-package-manager). Using simdjson as a CMake dependency ------------------ You can include the simdjson as a CMake dependency by including the following lines in your `CMakeLists.txt`: ```cmake include(FetchContent) FetchContent_Declare( simdjson GIT_REPOSITORY https://github.com/simdjson/simdjson.git GIT_TAG v0.5.0 GIT_SHALLOW TRUE) set(SIMDJSON_JUST_LIBRARY ON CACHE INTERNAL "") set(SIMDJSON_BUILD_STATIC ON CACHE INTERNAL "") FetchContent_MakeAvailable(simdjson) ``` You should replace `GIT_TAG v0.5.0` by the version you need. If you omit `GIT_TAG v0.5.0`, you will work from the main branch of simdjson: we recommend that if you are working on production code, Elsewhere in your project, you can declare dependencies on simdjson with lines such as these: ```cmake add_executable(myprogram myprogram.cpp) target_link_libraries(myprogram simdjson) ``` We recommend CMake version 3.15 or better. See [our CMake demonstration](https://github.com/simdjson/cmake_demo_single_file). It works under Linux, FreeBSD, macOS and Windows (including Visual Studio). The CMake build in simdjson can be taylored with a few variables. You can see the available variables and their default values by entering the `cmake -LA` command. The Basics: Loading and Parsing JSON Documents ---------------------------------------------- The simdjson library offers a simple DOM tree API, which you can access by creating a `dom::parser` and calling the `load()` method: ```c++ dom::parser parser; dom::element doc = parser.load(filename); // load and parse a file ``` Or by creating a padded string (for efficiency reasons, simdjson requires a string with SIMDJSON_PADDING bytes at the end) and calling `parse()`: ```c++ dom::parser parser; dom::element doc = parser.parse("[1,2,3]"_padded); // parse a string ``` The parsed document resulting from the `parser.load` and `parser.parse` calls depends on the `parser` instance. Thus the `parser` instance must remain in scope. Furthermore, you must have at most one parsed document in play per `parser` instance. During the`load` or `parse` calls, neither the input file nor the input string are ever modified. After calling `load` or `parse`, the source (either a file or a string) can be safely discarded. All of the JSON data is stored in the `parser` instance. The parsed document is also immutable in simdjson: you do not modify it by accessing it. For best performance, a `parser` instance should be reused over several files: otherwise you will needlessly reallocate memory, an expensive process. It is also possible to avoid entirely memory allocations during parsing when using simdjson. [See our performance notes for details](performance.md). Using the Parsed JSON --------------------- Once you have an element, you can navigate it with idiomatic C++ iterators, operators and casts. * **Extracting Values (with exceptions):** You can cast a JSON element to a native type: `double(element)` or `double x = json_element`. This works for double, uint64_t, int64_t, bool, dom::object and dom::array. An exception is thrown if the cast is not possible. * **Extracting Values (without expceptions):** You can use a variant usage of `get()` with error codes to avoid exceptions. You first declare the variable of the appropriate type (`double`, `uint64_t`, `int64_t`, `bool`, `dom::object` and `dom::array`) and pass it by reference to `get()` which gives you back an error code: e.g., ```c++ simdjson::error_code error; simdjson::padded_string numberstring = "1.2"_padded; // our JSON input ("1.2") simdjson::dom::parser parser; double value; // variable where we store the value to be parsed error = parser.parse(numberstring).get(value); if (error) { std::cerr << error << std::endl; return EXIT_FAILURE; } std::cout << "I parsed " << value << " from " << numberstring.data() << std::endl; ``` * **Field Access:** To get the value of the "foo" field in an object, use `object["foo"]`. * **Array Iteration:** To iterate through an array, use `for (auto value : array) { ... }`. If you know the type of the value, you can cast it right there, too! `for (double value : array) { ... }` * **Object Iteration:** You can iterate through an object's fields, too: `for (auto [key, value] : object)` * **Array Index:** To get at an array value by index, use the at() method: `array.at(0)` gets the first element. > Note that array[0] does not compile, because implementing [] gives the impression indexing is a > O(1) operation, which it is not presently in simdjson. Instead, you should iterate over the elements > using a for-loop, as in our examples. * **Array and Object size** Given an array or an object, you can get its size (number of elements or keys) with the `size()` method. * **Checking an Element Type:** You can check an element's type with `element.type()`. It returns an `element_type`. * **Output to streams and strings:** Given a document or an element (or node) out of a JSON document, you can output a minified string version using the C++ stream idiom (`out << element`). You can also request the construction of a minified string version (`simdjson::minify(element)`). Here are some examples of all of the above: ```c++ auto cars_json = R"( [ { "make": "Toyota", "model": "Camry", "year": 2018, "tire_pressure": [ 40.1, 39.9, 37.7, 40.4 ] }, { "make": "Kia", "model": "Soul", "year": 2012, "tire_pressure": [ 30.1, 31.0, 28.6, 28.7 ] }, { "make": "Toyota", "model": "Tercel", "year": 1999, "tire_pressure": [ 29.8, 30.0, 30.2, 30.5 ] } ] )"_padded; dom::parser parser; // Iterating through an array of objects for (dom::object car : parser.parse(cars_json)) { // Accessing a field by name cout << "Make/Model: " << car["make"] << "/" << car["model"] << endl; // Casting a JSON element to an integer uint64_t year = car["year"]; cout << "- This car is " << 2020 - year << "years old." << endl; // Iterating through an array of floats double total_tire_pressure = 0; for (double tire_pressure : car["tire_pressure"]) { total_tire_pressure += tire_pressure; } cout << "- Average tire pressure: " << (total_tire_pressure / 4) << endl; // Writing out all the information about the car for (auto field : car) { cout << "- " << field.key << ": " << field.value << endl; } } ``` Here is a different example illustrating the same ideas: ```C++ auto abstract_json = R"( [ { "12345" : {"a":12.34, "b":56.78, "c": 9998877} }, { "12545" : {"a":11.44, "b":12.78, "c": 11111111} } ] )"_padded; dom::parser parser; // Parse and iterate through an array of objects for (dom::object obj : parser.parse(abstract_json)) { for(const auto& key_value : obj) { cout << "key: " << key_value.key << " : "; dom::object innerobj = key_value.value; cout << "a: " << double(innerobj["a"]) << ", "; cout << "b: " << double(innerobj["b"]) << ", "; cout << "c: " << int64_t(innerobj["c"]) << endl; } } ``` And another one: ```C++ auto abstract_json = R"( { "str" : { "123" : {"abc" : 3.14 } } } )"_padded; dom::parser parser; double v = parser.parse(abstract_json)["str"]["123"]["abc"]; cout << "number: " << v << endl; ``` C++11 Support and string_view ------------- The simdjson library builds on compilers supporting the [C++11 standard](https://en.wikipedia.org/wiki/C%2B%2B11). It is also a strict requirement: we have no plan to support older C++ compilers. We represent parsed strings in simdjson using the `std::string_view` class. It avoids the need to copy the data, as would be necessary with the `std::string` class. It also avoids the pitfalls of null-terminated C strings. The `std::string_view` class has become standard as part of C++17 but it is not always available on compilers which only supports C++11. When we detect that `string_view` is natively available, we define the macro `SIMDJSON_HAS_STRING_VIEW`. When we detect that it is unavailable, we use [string-view-lite](https://github.com/martinmoene/string-view-lite) as a substitute. In such cases, we use the type alias `using string_view = nonstd::string_view;` to offer the same API, irrespective of the compiler and standard library. The macro `SIMDJSON_HAS_STRING_VIEW` will be *undefined* to indicate that we emulate `string_view`. C++17 Support ------------- While the simdjson library can be used in any project using C++ 11 and above, field iteration has special support C++ 17's destructuring syntax. For example: ```c++ padded_string json = R"( { "foo": 1, "bar": 2 } )"_padded; dom::parser parser; dom::object object; auto error = parser.parse(json).get(object); if (error) { cerr << error << endl; return; } for (auto [key, value] : object) { cout << key << " = " << value << endl; } ``` For comparison, here is the C++ 11 version of the same code: ```c++ // C++ 11 version for comparison padded_string json = R"( { "foo": 1, "bar": 2 } )"_padded; dom::parser parser; dom::object object; auto error = parser.parse(json).get(object); if (error) { cerr << error << endl; return; } for (dom::key_value_pair field : object) { cout << field.key << " = " << field.value << endl; } ``` Minifying JSON strings without parsing ---------------------- In some cases, you may have valid JSON strings that you do not wish to parse but that you wish to minify. That is, you wish to remove all unnecessary spaces. We have a fast function for this purpose (`simdjson::minify(const char * input, size_t length, const char * output, size_t& new_length)`). This function does not validate your content, and it does not parse it. It is much faster than parsing the string and re-serializing it in minified form (`simdjson::minify(parser.parse())`). Usage is relatively simple. You must pass an input pointer with a length parameter, as well as an output pointer and an output length parameter (by reference). The output length parameter is not read, but written to. The output pointer should point to a valid memory region that is as large as the original string length. The input pointer and input length are read, but not written to. ```C++ // Starts with a valid JSON document as a string. // It does not have to be null-terminated. const char * some_string = "[ 1, 2, 3, 4] "; size_t length = std::strlen(some_string); // Create a buffer to receive the minified string. Make sure that there is enough room (length bytes). std::unique_ptr buffer{new char[length]}; size_t new_length{}; // It will receive the minified length. auto error = simdjson::minify(some_string, length, buffer.get(), new_length); // The buffer variable now has "[1,2,3,4]" and new_length has value 9. ``` Though it does not validate the JSON input, it will detect when the document ends with an unterminated string. E.g., it would refuse to minify the string `"this string is not terminated` because of the missing final quote. UTF-8 validation (alone) ---------------------- The simdjson library has fast functions to validate UTF-8 strings. They are many times faster than most functions commonly found in libraries. You can use our fast functions, even if you do not care about JSON. ```C++ const char * some_string = "[ 1, 2, 3, 4] "; size_t length = std::strlen(some_string); bool is_ok = simdjson::validate_utf8(some_string, length); ``` The UTF-8 validation function merely checks that the input is valid UTF-8: it works with strings in general, not just JSON strings. Your input string does not need any padding. Any string will do. The `validate_utf8` function does not do any memory allocation on the heap, and it does not throw exceptions. JSON Pointer ------------ The simdjson library also supports [JSON pointer](https://tools.ietf.org/html/rfc6901) through the `at_pointer()` method, letting you reach further down into the document in a single call: ```c++ auto cars_json = R"( [ { "make": "Toyota", "model": "Camry", "year": 2018, "tire_pressure": [ 40.1, 39.9, 37.7, 40.4 ] }, { "make": "Kia", "model": "Soul", "year": 2012, "tire_pressure": [ 30.1, 31.0, 28.6, 28.7 ] }, { "make": "Toyota", "model": "Tercel", "year": 1999, "tire_pressure": [ 29.8, 30.0, 30.2, 30.5 ] } ] )"_padded; dom::parser parser; dom::element cars = parser.parse(cars_json); cout << cars.at_pointer("/0/tire_pressure/1") << endl; // Prints 39.9 ``` A JSON Path is a sequence of segments each starting with the '/' character. Within arrays, an integer index allows you to select the indexed node. Within objects, the string value of the key allows you to select the value. If your keys contain the characters '/' or '~', they must be escaped as '~1' and '~0' respectively. An empty JSON Path refers to the whole document. We also extend the JSON Pointer support to include *relative* paths. You can apply a JSON path to any node and the path gets interpreted relatively, as if the currrent node were a whole JSON document. Consider the following example: ```c++ auto cars_json = R"( [ { "make": "Toyota", "model": "Camry", "year": 2018, "tire_pressure": [ 40.1, 39.9, 37.7, 40.4 ] }, { "make": "Kia", "model": "Soul", "year": 2012, "tire_pressure": [ 30.1, 31.0, 28.6, 28.7 ] }, { "make": "Toyota", "model": "Tercel", "year": 1999, "tire_pressure": [ 29.8, 30.0, 30.2, 30.5 ] } ] )"_padded; dom::parser parser; dom::element cars = parser.parse(cars_json); cout << cars.at_pointer("/0/tire_pressure/1") << endl; // Prints 39.9 for (dom::element car_element : cars) { dom::object car; simdjson::error_code error; if ((error = car_element.get(car))) { std::cerr << error << std::endl; return; } double x = car.at_pointer("/tire_pressure/1"); cout << x << endl; // Prints 39.9, 31 and 30 } ``` Error Handling -------------- All simdjson APIs that can fail return `simdjson_result`, which is a <value, error_code> pair. You can retrieve the value with .get(), like so: ```c++ dom::element doc; auto error = parser.parse(json).get(doc); if (error) { cerr << error << endl; exit(1); } ``` When you use the code this way, it is your responsibility to check for error before using the result: if there is an error, the result value will not be valid and using it will caused undefined behavior. We can write a "quick start" example where we attempt to parse a file and access some data, without triggering exceptions: ```C++ #include "simdjson.h" int main(void) { simdjson::dom::parser parser; simdjson::dom::element tweets; auto error = parser.load("twitter.json").get(tweets); if (error) { std::cerr << error << std::endl; return EXIT_FAILURE; } simdjson::dom::element res; if ((error = tweets["search_metadata"]["count"].get(res))) { std::cerr << "could not access keys" << std::endl; return EXIT_FAILURE; } std::cout << res << " results." << std::endl; } ``` ### Error Handling Example This is how the example in "Using the Parsed JSON" could be written using only error code checking: ```c++ auto cars_json = R"( [ { "make": "Toyota", "model": "Camry", "year": 2018, "tire_pressure": [ 40.1, 39.9, 37.7, 40.4 ] }, { "make": "Kia", "model": "Soul", "year": 2012, "tire_pressure": [ 30.1, 31.0, 28.6, 28.7 ] }, { "make": "Toyota", "model": "Tercel", "year": 1999, "tire_pressure": [ 29.8, 30.0, 30.2, 30.5 ] } ] )"_padded; dom::parser parser; dom::array cars; auto error = parser.parse(cars_json).get(cars); if (error) { cerr << error << endl; exit(1); } // Iterating through an array of objects for (dom::element car_element : cars) { dom::object car; if ((error = car_element.get(car))) { cerr << error << endl; exit(1); } // Accessing a field by name std::string_view make, model; if ((error = car["make"].get(make))) { cerr << error << endl; exit(1); } if ((error = car["model"].get(model))) { cerr << error << endl; exit(1); } cout << "Make/Model: " << make << "/" << model << endl; // Casting a JSON element to an integer uint64_t year; if ((error = car["year"].get(year))) { cerr << error << endl; exit(1); } cout << "- This car is " << 2020 - year << "years old." << endl; // Iterating through an array of floats double total_tire_pressure = 0; dom::array tire_pressure_array; if ((error = car["tire_pressure"].get(tire_pressure_array))) { cerr << error << endl; exit(1); } for (dom::element tire_pressure_element : tire_pressure_array) { double tire_pressure; if ((error = tire_pressure_element.get(tire_pressure))) { cerr << error << endl; exit(1); } total_tire_pressure += tire_pressure; } cout << "- Average tire pressure: " << (total_tire_pressure / 4) << endl; // Writing out all the information about the car for (auto field : car) { cout << "- " << field.key << ": " << field.value << endl; } } ``` Here is another example: ```C++ auto abstract_json = R"( [ { "12345" : {"a":12.34, "b":56.78, "c": 9998877} }, { "12545" : {"a":11.44, "b":12.78, "c": 11111111} } ] )"_padded; dom::parser parser; dom::array array; auto error = parser.parse(abstract_json).get(array); if (error) { cerr << error << endl; exit(1); } // Iterate through an array of objects for (dom::element elem : array) { dom::object obj; if ((error = elem.get(obj))) { cerr << error << endl; exit(1); } for (auto & key_value : obj) { cout << "key: " << key_value.key << " : "; dom::object innerobj; if ((error = key_value.value.get(innerobj))) { cerr << error << endl; exit(1); } double va, vb; if ((error = innerobj["a"].get(va))) { cerr << error << endl; exit(1); } cout << "a: " << va << ", "; if ((error = innerobj["b"].get(vc))) { cerr << error << endl; exit(1); } cout << "b: " << vb << ", "; int64_t vc; if ((error = innerobj["c"].get(vc))) { cerr << error << endl; exit(1); } cout << "c: " << vc << endl; } } ``` And another one: ```C++ auto abstract_json = R"( { "str" : { "123" : {"abc" : 3.14 } } } )"_padded; dom::parser parser; double v; auto error = parser.parse(abstract_json)["str"]["123"]["abc"].get(v); if (error) { cerr << error << endl; exit(1); } cout << "number: " << v << endl; ``` Notice how we can string several operations (`parser.parse(abstract_json)["str"]["123"]["abc"].get(v)`) and only check for the error once, a strategy we call *error chaining*. The next two functions will take as input a JSON document containing an array with a single element, either a string or a number. They return true upon success. ```C++ simdjson::dom::parser parser{}; bool parse_double(const char *j, double &d) { auto error = parser.parse(j, std::strlen(j)) .at(0) .get(d, error); if (error) { return false; } return true; } bool parse_string(const char *j, std::string &s) { std::string_view answer; auto error = parser.parse(j,strlen(j)) .at(0) .get(answer, error); if (error) { return false; } s.assign(answer.data(), answer.size()); return true; } ``` ### Exceptions Users more comfortable with an exception flow may choose to directly cast the `simdjson_result` to the desired type: ```c++ dom::element doc = parser.parse(json); // Throws an exception if there was an error! ``` When used this way, a `simdjson_error` exception will be thrown if an error occurs, preventing the program from continuing if there was an error. Tree Walking and JSON Element Types ----------------------------------- Sometimes you don't necessarily have a document with a known type, and are trying to generically inspect or walk over JSON elements. To do that, you can use iterators and the type() method. For example, here's a quick and dirty recursive function that verbosely prints the JSON document as JSON (* ignoring nuances like trailing commas and escaping strings, for brevity's sake): ```c++ void print_json(dom::element element) { switch (element.type()) { case dom::element_type::ARRAY: cout << "["; for (dom::element child : dom::array(element)) { print_json(child); cout << ","; } cout << "]"; break; case dom::element_type::OBJECT: cout << "{"; for (dom::key_value_pair field : dom::object(element)) { cout << "\"" << field.key << "\": "; print_json(field.value); } cout << "}"; break; case dom::element_type::INT64: cout << int64_t(element) << endl; break; case dom::element_type::UINT64: cout << uint64_t(element) << endl; break; case dom::element_type::DOUBLE: cout << double(element) << endl; break; case dom::element_type::STRING: cout << std::string_view(element) << endl; break; case dom::element_type::BOOL: cout << bool(element) << endl; break; case dom::element_type::NULL_VALUE: cout << "null" << endl; break; } } void basics_treewalk_1() { dom::parser parser; print_json(parser.load("twitter.json")); } ``` Newline-Delimited JSON (ndjson) and JSON lines ---------------------------------------------- The simdjson library also support multithreaded JSON streaming through a large file containing many smaller JSON documents in either [ndjson](http://ndjson.org) or [JSON lines](http://jsonlines.org) format. If your JSON documents all contain arrays or objects, we even support direct file concatenation without whitespace. The concatenated file has no size restrictions (including larger than 4GB), though each individual document must be no larger than 4 GB. Here is a simple example, given "x.json" with this content: ```json { "foo": 1 } { "foo": 2 } { "foo": 3 } ``` ```c++ dom::parser parser; dom::document_stream docs = parser.load_many("x.json"); for (dom::element doc : docs) { cout << doc["foo"] << endl; } // Prints 1 2 3 ``` In-memory ndjson strings can be parsed as well, with `parser.parse_many(string)`: ```c++ dom::parser parser; auto json = R"({ "foo": 1 } { "foo": 2 } { "foo": 3 })"_padded; dom::document_stream docs = parser.parse_many(json); for (dom::element doc : docs) { cout << doc["foo"] << endl; } // Prints 1 2 3 ``` Unlike `parser.parse`, both `parser.load_many(filename)` and `parser.parse_many(string)` may parse "on demand" (lazily). That is, no parsing may have been done before you enter the loop `for (dom::element doc : docs) {` and you should expect the parser to only ever fully parse one JSON document at a time. 1. When calling `parser.load_many(filename)`, the file's content is loaded up in a memory buffer owned by the `parser`'s instance. Thus the file can be safely deleted after calling `parser.load_many(filename)` as the parser instance owns all of the data. 2. When calling `parser.parse_many(string)`, no copy is made of the provided string input. The provided memory buffer may be accessed each time a JSON document is parsed. Calling `parser.parse_many(string)` on a temporary string buffer (e.g., `docs = parser.parse_many("[1,2,3]"_padded)`) is unsafe (and will not compile) because the `document_stream` instance needs access to the buffer to return the JSON documents. In constrast, calling `doc = parser.parse("[1,2,3]"_padded)` is safe because `parser.parse` eagerly parses the input. Both `load_many` and `parse_many` take an optional parameter `size_t batch_size` which defines the window processing size. It is set by default to a large value (`1000000` corresponding to 1 MB). None of your JSON documents should exceed this window size, or else you will get the error `simdjson::CAPACITY`. You cannot set this window size larger than 4 GB: you will get the error `simdjson::CAPACITY`. The smaller the window size is, the less memory the function will use. Setting the window size too small (e.g., less than 100 kB) may also impact performance negatively. Leaving it to 1 MB is expected to be a good choice, unless you have some larger documents. See [parse_many.md](parse_many.md) for detailed information and design. Thread Safety ------------- We built simdjson with thread safety in mind. The simdjson library is single-threaded except for [`parse_many`](parse_many.md) which may use secondary threads under its control when the library is compiled with thread support. We recommend using one `dom::parser` object per thread in which case the library is thread-safe. It is unsafe to reuse a `dom::parser` object between different threads. The parsed results (`dom::document`, `dom::element`, `array`, `object`) depend on the `dom::parser`, etc. therefore it is also potentially unsafe to use the result of the parsing between different threads. The CPU detection, which runs the first time parsing is attempted and switches to the fastest parser for your CPU, is transparent and thread-safe. Standard Compliance -------------------- The simdjson library is fully compliant with the [RFC 8259](https://www.tbray.org/ongoing/When/201x/2017/12/14/rfc8259.html) JSON specification. - The only insignificant whitespace characters allowed are the space, the horizontal tab, the line feed and the carriage return. In particular, a JSON document may not contain an unespaced null character. - A single string or a single number is considered to be a valid JSON document. - We fully validate the numbers according to the JSON specification. For example, the string `01` is not valid JSON document since the specification states that *leading zeros are not allowed*. - The specification allows implementations to set limits on the range and precision of numbers accepted. We support 64-bit floating-point numbers as well as integer values. - We parse integers and floating-point numbers as separate types which allows us to support all signed (two complement's) 64-bit integers, like a Java `long` or a C/C++ `long long` and all 64-bit unsigned integers. When we cannot represent exactly an integer as a signed or unsigned 64-bit value, we reject the JSON document. - We support the full range of 64-bit floating-point numbers (binary64). The values range from `std::numeric_limits::lowest()` to `std::numeric_limits::max()`, so from -1.7976e308 all the way to 1.7975e308. Extreme values (less or equal to -1e308, greater or equal to 1e308) are rejected: we refuse to parse the input document. Numbers are parsed with with a perfect accuracy (ULP 0): the nearest floating-point value is chosen, rounding to even when needed. If you serialized your floating-point numbers with 17 significant digits in a standard compliant manner, the simdjson library is guaranteed to recovere the example same numbers, exactly. - The specification states that JSON text exchanged between systems that are not part of a closed ecosystem MUST be encoded using UTF-8. The simdjson library does full UTF-8 validation as part of the parsing. The specification states that implementations MUST NOT add a byte order mark: the simdjson library rejects documents starting with a byte order mark. - The simdjson library validates string content for unescaped characters. Unescaped line breaks and tabs in strings are not allowed. - The simdjson library accepts objects with repeated keys: all of the name/value pairs, including duplicates, are reported. We do not enforce key uniqueness. - The specification states that an implementation may set limits on the size of texts that it accepts. The simdjson library limits single JSON documents to 4 GiB. It will refuse to parse a JSON document larger than 4294967295 bytes. (This limitation does not apply to streams of JSON documents, only to single JSON documents.) - The specification states that an implementation may set limits on the maximum depth of nesting. By default, the simdjson will refuse to parse documents with a depth exceeding 1024. Backwards Compatibility ----------------------- The only header file supported by simdjson is `simdjson.h`. Older versions of simdjson published a number of other include files such as `document.h` or `ParsedJson.h` alongside `simdjson.h`; these headers may be moved or removed in future versions.