There are myriads of JSON libraries out there, and each may even have its reason to exist. Our class had these design goals:
Intuitive syntax. In languages such as Python, JSON feels like a first class data type. We used all the operator magic of modern C++ to achieve the same feeling in your code. Check out the examples below and you'll know what I mean.
Trivial integration. Our whole code consists of a single header file json.hpp
. That's it. No library, no subproject, no dependencies, no complex build system. The class is written in vanilla C++11. All in all, everything should require no adjustment of your compiler flags or project settings.
Serious testing. Our class is heavily unit-tested and covers 100% of the code, including all exceptional behavior. Furthermore, we checked with Valgrind and the Clang Sanitizers that there are no memory leaks. Google OSS-Fuzz additionally runs fuzz tests agains all parsers 24/7, effectively executing billions of tests so far. To maintain high quality, the project is following the Core Infrastructure Initiative (CII) best practices.
Other aspects were not so important to us:
Memory efficiency. Each JSON object has an overhead of one pointer (the maximal size of a union) and one enumeration element (1 byte). The default generalization uses the following C++ data types: std::string
for strings, int64_t
, uint64_t
or double
for numbers, std::map
for objects, std::vector
for arrays, and bool
for Booleans. However, you can template the generalized class basic_json
to your needs.
Speed. There are certainly faster JSON libraries out there. However, if your goal is to speed up your development by adding JSON support with a single header, then this library is the way to go. If you know how to use a std::vector
or std::map
, you are already set.
See the contribution guidelines for more information.
json.hpp
is the single required file in single_include/nlohmann
or released here. You need to add
#include <nlohmann/json.hpp> // for convenience using json = nlohmann::json;
to the files you want to process JSON and set the necessary switches to enable C++11 (e.g., -std=c++11
for GCC and Clang).
You can further use file include/nlohmann/json_fwd.hpp
for forward-declarations. The installation of json_fwd.hpp (as part of cmake's install step), can be achieved by setting -DJSON_MultipleHeaders=ON
.
You can also use the nlohmann_json::nlohmann_json
interface target in CMake. This target populates the appropriate usage requirements for INTERFACE_INCLUDE_DIRECTORIES
to point to the appropriate include directories and INTERFACE_COMPILE_FEATURES
for the necessary C++11 flags.
To use this library from a CMake project, you can locate it directly with find_package()
and use the namespaced imported target from the generated package configuration:
# CMakeLists.txt find_package(nlohmann_json 3.2.0 REQUIRED) ... add_library(foo ...) ... target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json)
The package configuration file, nlohmann_jsonConfig.cmake
, can be used either from an install tree or directly out of the build tree.
To embed the library directly into an existing CMake project, place the entire source tree in a subdirectory and call add_subdirectory()
in your CMakeLists.txt
file:
# Typically you don't care so much for a third party library's tests to be # run from your own project's code. set(JSON_BuildTests OFF CACHE INTERNAL "") # Don't use include(nlohmann_json/CMakeLists.txt) since that carries with it # inintended consequences that will break the build. It's generally # discouraged (although not necessarily well documented as such) to use # include(...) for pulling in other CMake projects anyways. add_subdirectory(nlohmann_json) ... add_library(foo ...) ... target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json)
To allow your project to support either an externally supplied or an embedded JSON library, you can use a pattern akin to the following:
# Top level CMakeLists.txt project(FOO) ... option(FOO_USE_EXTERNAL_JSON "Use an external JSON library" OFF) ... add_subdirectory(thirdparty) ... add_library(foo ...) ... # Note that the namespaced target will always be available regardless of the # import method target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json)
# thirdparty/CMakeLists.txt ... if(FOO_USE_EXTERNAL_JSON) find_package(nlohmann_json 3.2.0 REQUIRED) else() set(JSON_BuildTests OFF CACHE INTERNAL "") add_subdirectory(nlohmann_json) endif() ...
thirdparty/nlohmann_json
is then a complete copy of this source tree.
:beer: If you are using OS X and Homebrew, just type brew tap nlohmann/json
and brew install nlohmann_json
and you're set. If you want the bleeding edge rather than the latest release, use brew install nlohmann_json --HEAD
.
If you are using the Meson Build System, then you can wrap this repository as a subproject.
If you are using Conan to manage your dependencies, merely add jsonformoderncpp/x.y.z@vthiery/stable
to your conanfile.py
's requires, where x.y.z
is the release version you want to use. Please file issues here if you experience problems with the packages.
If you are using Spack to manage your dependencies, you can use the nlohmann_json
package. Please see the spack project for any issues regarding the packaging.
If you are using hunter on your project for external dependencies, then you can use the nlohmann_json package. Please see the hunter project for any issues regarding the packaging.
If you are using Buckaroo, you can install this library's module with buckaroo install nlohmann/json
. Please file issues here.
If you are using vcpkg on your project for external dependencies, then you can use the nlohmann-json package. Please see the vcpkg project for any issues regarding the packaging.
If you are using cget, you can install the latest development version with cget install nlohmann/json
. A specific version can be installed with cget install nlohmann/json@v3.1.0
. Also, the multiple header version can be installed by adding the -DJSON_MultipleHeaders=ON
flag (i.e., cget install nlohmann/json -DJSON_MultipleHeaders=ON
).
If you are using CocoaPods, you can use the library by adding pod "nlohmann_json", '~>3.1.2'
to your podfile (see an example). Please file issues here.
Beside the examples below, you may want to check the documentation where each function contains a separate code example (e.g., check out emplace()
). All example files can be compiled and executed on their own (e.g., file emplace.cpp).
Here are some examples to give you an idea how to use the class.
Assume you want to create the JSON object
{ "pi": 3.141, "happy": true, "name": "Niels", "nothing": null, "answer": { "everything": 42 }, "list": [1, 0, 2], "object": { "currency": "USD", "value": 42.99 } }
With this library, you could write:
// create an empty structure (null) json j; // add a number that is stored as double (note the implicit conversion of j to an object) j["pi"] = 3.141; // add a Boolean that is stored as bool j["happy"] = true; // add a string that is stored as std::string j["name"] = "Niels"; // add another null object by passing nullptr j["nothing"] = nullptr; // add an object inside the object j["answer"]["everything"] = 42; // add an array that is stored as std::vector (using an initializer list) j["list"] = { 1, 0, 2 }; // add another object (using an initializer list of pairs) j["object"] = { {"currency", "USD"}, {"value", 42.99} }; // instead, you could also write (which looks very similar to the JSON above) json j2 = { {"pi", 3.141}, {"happy", true}, {"name", "Niels"}, {"nothing", nullptr}, {"answer", { {"everything", 42} }}, {"list", {1, 0, 2}}, {"object", { {"currency", "USD"}, {"value", 42.99} }} };
Note that in all these cases, you never need to “tell” the compiler which JSON value type you want to use. If you want to be explicit or express some edge cases, the functions json::array
and json::object
will help:
// a way to express the empty array [] json empty_array_explicit = json::array(); // ways to express the empty object {} json empty_object_implicit = json({}); json empty_object_explicit = json::object(); // a way to express an _array_ of key/value pairs [["currency", "USD"], ["value", 42.99]] json array_not_object = json::array({ {"currency", "USD"}, {"value", 42.99} });
You can create a JSON value (deserialization) by appending _json
to a string literal:
// create object from string literal json j = "{ \"happy\": true, \"pi\": 3.141 }"_json; // or even nicer with a raw string literal auto j2 = R"( { "happy": true, "pi": 3.141 } )"_json;
Note that without appending the _json
suffix, the passed string literal is not parsed, but just used as JSON string value. That is, json j = "{ \"happy\": true, \"pi\": 3.141 }"
would just store the string "{ "happy": true, "pi": 3.141 }"
rather than parsing the actual object.
The above example can also be expressed explicitly using json::parse()
:
// parse explicitly auto j3 = json::parse("{ \"happy\": true, \"pi\": 3.141 }");
You can also get a string representation of a JSON value (serialize):
// explicit conversion to string std::string s = j.dump(); // {\"happy\":true,\"pi\":3.141} // serialization with pretty printing // pass in the amount of spaces to indent std::cout << j.dump(4) << std::endl; // { // "happy": true, // "pi": 3.141 // }
Note the difference between serialization and assignment:
// store a string in a JSON value json j_string = "this is a string"; // retrieve the string value (implicit JSON to std::string conversion) std::string cpp_string = j_string; // retrieve the string value (explicit JSON to std::string conversion) auto cpp_string2 = j_string.get<std::string>(); // retrieve the string value (alternative explicit JSON to std::string conversion) std::string cpp_string3; j_string.get_to(cpp_string3); // retrieve the serialized value (explicit JSON serialization) std::string serialized_string = j_string.dump(); // output of original string std::cout << cpp_string << " == " << cpp_string2 << " == " << cpp_string3 << " == " << j_string.get<std::string>() << '\n'; // output of serialized value std::cout << j_string << " == " << serialized_string << std::endl;
.dump()
always returns the serialized value, and .get<std::string>()
returns the originally stored string value.
Note the library only supports UTF-8. When you store strings with different encodings in the library, calling dump()
may throw an exception.
You can also use streams to serialize and deserialize:
// deserialize from standard input json j; std::cin >> j; // serialize to standard output std::cout << j; // the setw manipulator was overloaded to set the indentation for pretty printing std::cout << std::setw(4) << j << std::endl;
These operators work for any subclasses of std::istream
or std::ostream
. Here is the same example with files:
// read a JSON file std::ifstream i("file.json"); json j; i >> j; // write prettified JSON to another file std::ofstream o("pretty.json"); o << std::setw(4) << j << std::endl;
Please note that setting the exception bit for failbit
is inappropriate for this use case. It will result in program termination due to the noexcept
specifier in use.
You can also parse JSON from an iterator range; that is, from any container accessible by iterators whose content is stored as contiguous byte sequence, for instance a std::vector<std::uint8_t>
:
std::vector<std::uint8_t> v = {'t', 'r', 'u', 'e'}; json j = json::parse(v.begin(), v.end());
You may leave the iterators for the range [begin, end):
std::vector<std::uint8_t> v = {'t', 'r', 'u', 'e'}; json j = json::parse(v);
The library uses a SAX-like interface with the following functions:
// called when null is parsed bool null(); // called when a boolean is parsed; value is passed bool boolean(bool val); // called when a signed or unsigned integer number is parsed; value is passed bool number_integer(number_integer_t val); bool number_unsigned(number_unsigned_t val); // called when a floating-point number is parsed; value and original string is passed bool number_float(number_float_t val, const string_t& s); // called when a string is parsed; value is passed and can be safely moved away bool string(string_t& val); // called when an object or array begins or ends, resp. The number of elements is passed (or -1 if not known) bool start_object(std::size_t elements); bool end_object(); bool start_array(std::size_t elements); bool end_array(); // called when an object key is parsed; value is passed and can be safely moved away bool key(string_t& val); // called when a parse error occurs; byte position, the last token, and an exception is passed bool parse_error(std::size_t position, const std::string& last_token, const detail::exception& ex);
The return value of each function determines whether parsing should proceed.
To implement your own SAX handler, proceed as follows:
nlohmann::json_sax<json>
as base class, but you can also use any class where the functions described above are implemented and public.my_sax
.bool json::sax_parse(input, &my_sax)
; where the first parameter can be any input like a string or an input stream and the second parameter is a pointer to your SAX interface.Note the sax_parse
function only returns a bool
indicating the result of the last executed SAX event. It does not return a json
value - it is up to you to decide what to do with the SAX events. Furthermore, no exceptions are thrown in case of a parse error - it is up to you what to do with the exception object passed to your parse_error
implementation. Internally, the SAX interface is used for the DOM parser (class json_sax_dom_parser
) as well as the acceptor (json_sax_acceptor
), see file json_sax.hpp
.
We designed the JSON class to behave just like an STL container. In fact, it satisfies the ReversibleContainer requirement.
// create an array using push_back json j; j.push_back("foo"); j.push_back(1); j.push_back(true); // also use emplace_back j.emplace_back(1.78); // iterate the array for (json::iterator it = j.begin(); it != j.end(); ++it) { std::cout << *it << '\n'; } // range-based for for (auto& element : j) { std::cout << element << '\n'; } // getter/setter const std::string tmp = j[0]; j[1] = 42; bool foo = j.at(2); // comparison j == "[\"foo\", 1, true]"_json; // true // other stuff j.size(); // 3 entries j.empty(); // false j.type(); // json::value_t::array j.clear(); // the array is empty again // convenience type checkers j.is_null(); j.is_boolean(); j.is_number(); j.is_object(); j.is_array(); j.is_string(); // create an object json o; o["foo"] = 23; o["bar"] = false; o["baz"] = 3.141; // also use emplace o.emplace("weather", "sunny"); // special iterator member functions for objects for (json::iterator it = o.begin(); it != o.end(); ++it) { std::cout << it.key() << " : " << it.value() << "\n"; } // find an entry if (o.find("foo") != o.end()) { // there is an entry with key "foo" } // or simpler using count() int foo_present = o.count("foo"); // 1 int fob_present = o.count("fob"); // 0 // delete an entry o.erase("foo");
Any sequence container (std::array
, std::vector
, std::deque
, std::forward_list
, std::list
) whose values can be used to construct JSON values (e.g., integers, floating point numbers, Booleans, string types, or again STL containers described in this section) can be used to create a JSON array. The same holds for similar associative containers (std::set
, std::multiset
, std::unordered_set
, std::unordered_multiset
), but in these cases the order of the elements of the array depends on how the elements are ordered in the respective STL container.
std::vector<int> c_vector {1, 2, 3, 4}; json j_vec(c_vector); // [1, 2, 3, 4] std::deque<double> c_deque {1.2, 2.3, 3.4, 5.6}; json j_deque(c_deque); // [1.2, 2.3, 3.4, 5.6] std::list<bool> c_list {true, true, false, true}; json j_list(c_list); // [true, true, false, true] std::forward_list<int64_t> c_flist {12345678909876, 23456789098765, 34567890987654, 45678909876543}; json j_flist(c_flist); // [12345678909876, 23456789098765, 34567890987654, 45678909876543] std::array<unsigned long, 4> c_array {{1, 2, 3, 4}}; json j_array(c_array); // [1, 2, 3, 4] std::set<std::string> c_set {"one", "two", "three", "four", "one"}; json j_set(c_set); // only one entry for "one" is used // ["four", "one", "three", "two"] std::unordered_set<std::string> c_uset {"one", "two", "three", "four", "one"}; json j_uset(c_uset); // only one entry for "one" is used // maybe ["two", "three", "four", "one"] std::multiset<std::string> c_mset {"one", "two", "one", "four"}; json j_mset(c_mset); // both entries for "one" are used // maybe ["one", "two", "one", "four"] std::unordered_multiset<std::string> c_umset {"one", "two", "one", "four"}; json j_umset(c_umset); // both entries for "one" are used // maybe ["one", "two", "one", "four"]
Likewise, any associative key-value containers (std::map
, std::multimap
, std::unordered_map
, std::unordered_multimap
) whose keys can construct an std::string
and whose values can be used to construct JSON values (see examples above) can be used to create a JSON object. Note that in case of multimaps only one key is used in the JSON object and the value depends on the internal order of the STL container.
std::map<std::string, int> c_map { {"one", 1}, {"two", 2}, {"three", 3} }; json j_map(c_map); // {"one": 1, "three": 3, "two": 2 } std::unordered_map<const char*, double> c_umap { {"one", 1.2}, {"two", 2.3}, {"three", 3.4} }; json j_umap(c_umap); // {"one": 1.2, "two": 2.3, "three": 3.4} std::multimap<std::string, bool> c_mmap { {"one", true}, {"two", true}, {"three", false}, {"three", true} }; json j_mmap(c_mmap); // only one entry for key "three" is used // maybe {"one": true, "two": true, "three": true} std::unordered_multimap<std::string, bool> c_ummap { {"one", true}, {"two", true}, {"three", false}, {"three", true} }; json j_ummap(c_ummap); // only one entry for key "three" is used // maybe {"one": true, "two": true, "three": true}
The library supports JSON Pointer (RFC 6901) as alternative means to address structured values. On top of this, JSON Patch (RFC 6902) allows to describe differences between two JSON values - effectively allowing patch and diff operations known from Unix.
// a JSON value json j_original = R"({ "baz": ["one", "two", "three"], "foo": "bar" })"_json; // access members with a JSON pointer (RFC 6901) j_original["/baz/1"_json_pointer]; // "two" // a JSON patch (RFC 6902) json j_patch = R"([ { "op": "replace", "path": "/baz", "value": "boo" }, { "op": "add", "path": "/hello", "value": ["world"] }, { "op": "remove", "path": "/foo"} ])"_json; // apply the patch json j_result = j_original.patch(j_patch); // { // "baz": "boo", // "hello": ["world"] // } // calculate a JSON patch from two JSON values json::diff(j_result, j_original); // [ // { "op":" replace", "path": "/baz", "value": ["one", "two", "three"] }, // { "op": "remove","path": "/hello" }, // { "op": "add", "path": "/foo", "value": "bar" } // ]
The library supports JSON Merge Patch (RFC 7386) as a patch format. Instead of using JSON Pointer (see above) to specify values to be manipulated, it describes the changes using a syntax that closely mimics the document being modified.
// a JSON value json j_document = R"({ "a": "b", "c": { "d": "e", "f": "g" } })"_json; // a patch json j_patch = R"({ "a":"z", "c": { "f": null } })"_json; // apply the patch j_original.merge_patch(j_patch); // { // "a": "z", // "c": { // "d": "e" // } // }
The type of the JSON object is determined automatically by the expression to store. Likewise, the stored value is implicitly converted.
// strings std::string s1 = "Hello, world!"; json js = s1; std::string s2 = js; // Booleans bool b1 = true; json jb = b1; bool b2 = jb; // numbers int i = 42; json jn = i; double f = jn; // etc.
You can also explicitly ask for the value:
std::string vs = js.get<std::string>(); bool vb = jb.get<bool>(); int vi = jn.get<int>(); // etc.
Note that char
types are not automatically converted to JSON strings, but to integer numbers. A conversion to a string must be specified explicitly:
char ch = 'A'; // ASCII value 65 json j_default = ch; // stores integer number 65 json j_string = std::string(1, ch); // stores string "A"
Every type can be serialized in JSON, not just STL containers and scalar types. Usually, you would do something along those lines:
namespace ns { // a simple struct to model a person struct person { std::string name; std::string address; int age; }; } ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60}; // convert to JSON: copy each value into the JSON object json j; j["name"] = p.name; j["address"] = p.address; j["age"] = p.age; // ... // convert from JSON: copy each value from the JSON object ns::person p { j["name"].get<std::string>(), j["address"].get<std::string>(), j["age"].get<int>() };
It works, but that‘s quite a lot of boilerplate... Fortunately, there’s a better way:
// create a person ns::person p {"Ned Flanders", "744 Evergreen Terrace", 60}; // conversion: person -> json json j = p; std::cout << j << std::endl; // {"address":"744 Evergreen Terrace","age":60,"name":"Ned Flanders"} // conversion: json -> person ns::person p2 = j; // that's it assert(p == p2);
To make this work with one of your types, you only need to provide two functions:
using nlohmann::json; namespace ns { void to_json(json& j, const person& p) { j = json{{"name", p.name}, {"address", p.address}, {"age", p.age}}; } void from_json(const json& j, person& p) { j.at("name").get_to(p.name); j.at("address").get_to(p.address); j.at("age").get_to(p.age); } } // namespace ns
That's all! When calling the json
constructor with your type, your custom to_json
method will be automatically called. Likewise, when calling get<your_type>()
or get_to(your_type&)
, the from_json
method will be called.
Some important things:
ns
, where person
is defined).get<your_type>()
, your_type
MUST be DefaultConstructible. (There is a way to bypass this requirement described later.)from_json
, use function at()
to access the object values rather than operator[]
. In case a key does not exist, at
throws an exception that you can handle, whereas operator[]
exhibits undefined behavior.operator=
definitions, code like your_variable = your_json;
may not compile. You need to write your_variable = your_json.get<decltype(your_variable)>();
or your_json.get_to(your_variable);
instead.std::vector
: the library already implements these.This requires a bit more advanced technique. But first, let's see how this conversion mechanism works:
The library uses JSON Serializers to convert types to json. The default serializer for nlohmann::json
is nlohmann::adl_serializer
(ADL means Argument-Dependent Lookup).
It is implemented like this (simplified):
template <typename T> struct adl_serializer { static void to_json(json& j, const T& value) { // calls the "to_json" method in T's namespace } static void from_json(const json& j, T& value) { // same thing, but with the "from_json" method } };
This serializer works fine when you have control over the type‘s namespace. However, what about boost::optional
or std::filesystem::path
(C++17)? Hijacking the boost
namespace is pretty bad, and it’s illegal to add something other than template specializations to std
...
To solve this, you need to add a specialization of adl_serializer
to the nlohmann
namespace, here's an example:
// partial specialization (full specialization works too) namespace nlohmann { template <typename T> struct adl_serializer<boost::optional<T>> { static void to_json(json& j, const boost::optional<T>& opt) { if (opt == boost::none) { j = nullptr; } else { j = *opt; // this will call adl_serializer<T>::to_json which will // find the free function to_json in T's namespace! } } static void from_json(const json& j, boost::optional<T>& opt) { if (j.is_null()) { opt = boost::none; } else { opt = j.get<T>(); // same as above, but with // adl_serializer<T>::from_json } } }; }
get()
for non-default constructible/non-copyable types?There is a way, if your type is MoveConstructible. You will need to specialize the adl_serializer
as well, but with a special from_json
overload:
struct move_only_type { move_only_type() = delete; move_only_type(int ii): i(ii) {} move_only_type(const move_only_type&) = delete; move_only_type(move_only_type&&) = default; int i; }; namespace nlohmann { template <> struct adl_serializer<move_only_type> { // note: the return type is no longer 'void', and the method only takes // one argument static move_only_type from_json(const json& j) { return {j.get<int>()}; } // Here's the catch! You must provide a to_json method! Otherwise you // will not be able to convert move_only_type to json, since you fully // specialized adl_serializer on that type static void to_json(json& j, move_only_type t) { j = t.i; } }; }
Yes. You might want to take a look at unit-udt.cpp
in the test suite, to see a few examples.
If you write your own serializer, you'll need to do a few things:
basic_json
alias than nlohmann::json
(the last template parameter of basic_json
is the JSONSerializer
)basic_json
alias (or a template parameter) in all your to_json
/from_json
methodsnlohmann::to_json
and nlohmann::from_json
when you need ADLHere is an example, without simplifications, that only accepts types with a size <= 32, and uses ADL.
// You should use void as a second template argument // if you don't need compile-time checks on T template<typename T, typename SFINAE = typename std::enable_if<sizeof(T) <= 32>::type> struct less_than_32_serializer { template <typename BasicJsonType> static void to_json(BasicJsonType& j, T value) { // we want to use ADL, and call the correct to_json overload using nlohmann::to_json; // this method is called by adl_serializer, // this is where the magic happens to_json(j, value); } template <typename BasicJsonType> static void from_json(const BasicJsonType& j, T& value) { // same thing here using nlohmann::from_json; from_json(j, value); } };
Be very careful when reimplementing your serializer, you can stack overflow if you don't pay attention:
template <typename T, void> struct bad_serializer { template <typename BasicJsonType> static void to_json(BasicJsonType& j, const T& value) { // this calls BasicJsonType::json_serializer<T>::to_json(j, value); // if BasicJsonType::json_serializer == bad_serializer ... oops! j = value; } template <typename BasicJsonType> static void to_json(const BasicJsonType& j, T& value) { // this calls BasicJsonType::json_serializer<T>::from_json(j, value); // if BasicJsonType::json_serializer == bad_serializer ... oops! value = j.template get<T>(); // oops! } };
Though JSON is a ubiquitous data format, it is not a very compact format suitable for data exchange, for instance over a network. Hence, the library supports CBOR (Concise Binary Object Representation), MessagePack, and UBJSON (Universal Binary JSON Specification) to efficiently encode JSON values to byte vectors and to decode such vectors.
// create a JSON value json j = R"({"compact": true, "schema": 0})"_json; // serialize to CBOR std::vector<std::uint8_t> v_cbor = json::to_cbor(j); // 0xA2, 0x67, 0x63, 0x6F, 0x6D, 0x70, 0x61, 0x63, 0x74, 0xF5, 0x66, 0x73, 0x63, 0x68, 0x65, 0x6D, 0x61, 0x00 // roundtrip json j_from_cbor = json::from_cbor(v_cbor); // serialize to MessagePack std::vector<std::uint8_t> v_msgpack = json::to_msgpack(j); // 0x82, 0xA7, 0x63, 0x6F, 0x6D, 0x70, 0x61, 0x63, 0x74, 0xC3, 0xA6, 0x73, 0x63, 0x68, 0x65, 0x6D, 0x61, 0x00 // roundtrip json j_from_msgpack = json::from_msgpack(v_msgpack); // serialize to UBJSON std::vector<std::uint8_t> v_ubjson = json::to_ubjson(j); // 0x7B, 0x69, 0x07, 0x63, 0x6F, 0x6D, 0x70, 0x61, 0x63, 0x74, 0x54, 0x69, 0x06, 0x73, 0x63, 0x68, 0x65, 0x6D, 0x61, 0x69, 0x00, 0x7D // roundtrip json j_from_ubjson = json::from_ubjson(v_ubjson);
Though it's 2018 already, the support for C++11 is still a bit sparse. Currently, the following compilers are known to work:
I would be happy to learn about other compilers/versions.
Please note:
GCC 4.8 has a bug 57824): multiline raw strings cannot be the arguments to macros. Don't use multiline raw strings directly in macros with this compiler.
Android defaults to using very old compilers and C++ libraries. To fix this, add the following to your Application.mk
. This will switch to the LLVM C++ library, the Clang compiler, and enable C++11 and other features disabled by default.
APP_STL := c++_shared NDK_TOOLCHAIN_VERSION := clang3.6 APP_CPPFLAGS += -frtti -fexceptions
The code compiles successfully with Android NDK, Revision 9 - 11 (and possibly later) and CrystaX's Android NDK version 10.
For GCC running on MinGW or Android SDK, the error 'to_string' is not a member of 'std'
(or similarly, for strtod
) may occur. Note this is not an issue with the code, but rather with the compiler itself. On Android, see above to build with a newer environment. For MinGW, please refer to this site and this discussion for information on how to fix this bug. For Android NDK using APP_STL := gnustl_static
, please refer to this discussion.
Unsupported versions of GCC and Clang are rejected by #error
directives. This can be switched off by defining JSON_SKIP_UNSUPPORTED_COMPILER_CHECK
. Note that you can expect no support in this case.
The following compilers are currently used in continuous integration at Travis and AppVeyor:
Compiler | Operating System | Version String |
---|---|---|
GCC 4.8.5 | Ubuntu 14.04.5 LTS | g++-4.8 (Ubuntu 4.8.5-2ubuntu1~14.04.2) 4.8.5 |
GCC 4.9.4 | Ubuntu 14.04.1 LTS | g++-4.9 (Ubuntu 4.9.4-2ubuntu1~14.04.1) 4.9.4 |
GCC 5.5.0 | Ubuntu 14.04.1 LTS | g++-5 (Ubuntu 5.5.0-12ubuntu1~14.04) 5.5.0 20171010 |
GCC 6.4.0 | Ubuntu 14.04.1 LTS | g++-6 (Ubuntu 6.4.0-17ubuntu1~14.04) 6.4.0 20180424 |
GCC 7.3.0 | Ubuntu 14.04.1 LTS | g++-7 (Ubuntu 7.3.0-21ubuntu1~14.04) 7.3.0 |
GCC 7.3.0 | Windows Server 2012 R2 (x64) | g++ (x86_64-posix-seh-rev0, Built by MinGW-W64 project) 7.3.0 |
GCC 8.1.0 | Ubuntu 14.04.1 LTS | g++-8 (Ubuntu 8.1.0-5ubuntu1~14.04) 8.1.0 |
Clang 3.5.0 | Ubuntu 14.04.1 LTS | clang version 3.5.0-4ubuntu2~trusty2 (tags/RELEASE_350/final) (based on LLVM 3.5.0) |
Clang 3.6.2 | Ubuntu 14.04.1 LTS | clang version 3.6.2-svn240577-1~exp1 (branches/release_36) (based on LLVM 3.6.2) |
Clang 3.7.1 | Ubuntu 14.04.1 LTS | clang version 3.7.1-svn253571-1~exp1 (branches/release_37) (based on LLVM 3.7.1) |
Clang 3.8.0 | Ubuntu 14.04.1 LTS | clang version 3.8.0-2ubuntu3~trusty5 (tags/RELEASE_380/final) |
Clang 3.9.1 | Ubuntu 14.04.1 LTS | clang version 3.9.1-4ubuntu3~14.04.3 (tags/RELEASE_391/rc2) |
Clang 4.0.1 | Ubuntu 14.04.1 LTS | clang version 4.0.1-svn305264-1~exp1 (branches/release_40) |
Clang 5.0.2 | Ubuntu 14.04.1 LTS | clang version 5.0.2-svn328729-1 |
Clang 6.0.1 | Ubuntu 14.04.1 LTS | clang version 6.0.1-svn334776-1 |
Clang Xcode 6.4 | OSX 10.10.5 | Apple LLVM version 6.1.0 (clang-602.0.53) (based on LLVM 3.6.0svn) |
Clang Xcode 7.3 | OSX 10.11.6 | Apple LLVM version 7.3.0 (clang-703.0.31) |
Clang Xcode 8.0 | OSX 10.11.6 | Apple LLVM version 8.0.0 (clang-800.0.38) |
Clang Xcode 8.1 | OSX 10.12.6 | Apple LLVM version 8.0.0 (clang-800.0.42.1) |
Clang Xcode 8.2 | OSX 10.12.6 | Apple LLVM version 8.0.0 (clang-800.0.42.1) |
Clang Xcode 8.3 | OSX 10.11.6 | Apple LLVM version 8.1.0 (clang-802.0.38) |
Clang Xcode 9.0 | OSX 10.12.6 | Apple LLVM version 9.0.0 (clang-900.0.37) |
Clang Xcode 9.1 | OSX 10.12.6 | Apple LLVM version 9.0.0 (clang-900.0.38) |
Clang Xcode 9.2 | OSX 10.13.3 | Apple LLVM version 9.1.0 (clang-902.0.39.1) |
Clang Xcode 9.3 | OSX 10.13.3 | Apple LLVM version 9.1.0 (clang-902.0.39.2) |
Clang Xcode 10.0 | OSX 10.13.3 | Apple LLVM version 10.0.0 (clang-1000.11.45.2) |
Visual Studio 14 2015 | Windows Server 2012 R2 (x64) | Microsoft (R) Build Engine version 14.0.25420.1, MSVC 19.0.24215.1 |
Visual Studio 2017 | Windows Server 2016 | Microsoft (R) Build Engine version 15.7.180.61344, MSVC 19.14.26433.0 |
The class is licensed under the MIT License:
Copyright © 2013-2018 Niels Lohmann
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
The class contains the UTF-8 Decoder from Bjoern Hoehrmann which is licensed under the MIT License (see above). Copyright © 2008-2009 Björn Hoehrmann bjoern@hoehrmann.de
The class contains a slightly modified version of the Grisu2 algorithm from Florian Loitsch which is licensed under the MIT License (see above). Copyright © 2009 Florian Loitsch
If you have questions regarding the library, I would like to invite you to open an issue at GitHub. Please describe your request, problem, or question as detailed as possible, and also mention the version of the library you are using as well as the version of your compiler and operating system. Opening an issue at GitHub allows other users and contributors to this library to collaborate. For instance, I have little experience with MSVC, and most issues in this regard have been solved by a growing community. If you have a look at the closed issues, you will see that we react quite timely in most cases.
Only if your request would contain confidential information, please send me an email. For encrypted messages, please use this key.
Commits by Niels Lohmann and releases are signed with this PGP Key.
I deeply appreciate the help of the following people.
parse()
to accept an rvalue reference.get_ref()
function to get a reference to stored values.has_mapped_type
function.int64_t
and uint64_t
.std::multiset
.dump()
function.std::locale::classic()
to avoid too much locale joggling, found some nice performance improvements in the parser, improved the benchmarking code, and realized locale-independent number parsing and printing.nullptr
s.-Weffc++
warnings.std::min
.<iostream>
with <iosfwd>
.find()
and count()
..natvis
for the MSVC debug view.std::stringstream
.items()
function.JSON_INTERNAL_CATCH
to control the exception handling inside the library.find_package
without installing the library.Thanks a lot for helping out! Please let me know if I forgot someone.
The library itself consists of a single header file licensed under the MIT license. However, it is built, tested, documented, and whatnot using a lot of third-party tools and services. Thanks a lot!
The library is currently used in Apple macOS Sierra and iOS 10. I am not sure what they are using the library for, but I am happy that it runs on so many devices.
NDEBUG
, see the documentation of assert
. In particular, note operator[]
implements unchecked access for const objects: If the given key is not present, the behavior is undefined (think of a dereferenced null pointer) and yields an assertion failure if assertions are switched on. If you are not sure whether an element in an object exists, use checked access with the at()
function.double
may be used to store numbers which may yield floating-point exceptions in certain rare situations if floating-point exceptions have been unmasked in the calling code. These exceptions are not caused by the library and need to be fixed in the calling code, such as by re-masking the exceptions prior to calling library functions.\uDEAD
) will yield parse errors.std::string
), note that its length/size functions return the number of stored bytes rather than the number of characters or glyphs.-fno-rtti
compiler flag.-fno-exceptions
or by defining the symbol JSON_NOEXCEPTION
. In this case, exceptions are replaced by an abort()
call.tsl::ordered_map
(integration) or nlohmann::fifo_map
(integration).To compile and run the tests, you need to execute
$ mkdir build $ cd build $ cmake .. $ cmake --build . $ ctest --output-on-failure
For more information, have a look at the file .travis.yml.