One of the fastest JSON libraries in the world. Glaze reads and writes from C++ memory, simplifying interfaces and offering incredible performance.
Glaze also supports binary messages via BEVE and CSV support. And, the library has many more useful features for building APIs.
Glaze requires C++20, using concepts for cleaner code and more helpful errors.
- Simple registration
- Standard C++ library support
- Direct to memory serialization/deserialization
- Compile time maps with constant time lookups and perfect hashing
- Nearly zero intermediate allocations
- Powerful wrappers to modify read/write behavior (Wrappers)
- Use your own custom read/write functions (Custom Read/Write)
- Direct memory access through JSON pointer syntax
- Tagged binary spec through the same API for maximum performance
- No exceptions (compiles with
-fno-exceptions) - If you desire helpers that throw for cleaner syntax see Glaze Exceptions
- No runtime type information necessary (compiles with
-fno-rtti) - JSON-RPC 2.0 support
- JSON Schema generation
- CSV Reading/Writing
- Much more!
| Library | Roundtrip Time (s) | Write (MB/s) | Read (MB/s) |
|---|---|---|---|
| Glaze | 1.18 | 925 | 1141 |
| simdjson (on demand) | N/A | N/A | 1124 |
| yyjson | 1.48 | 722 | 912 |
| daw_json_link | 2.77 | 350 | 540 |
| RapidJSON | 3.57 | 270 | 435 |
| json_struct | 5.52 | 163 | 325 |
| Boost.JSON | 5.30 | 182 | 294 |
| nlohmann | 14.92 | 80 | 79 |
Performance test code available here
Note: simdjson is great, but can experience major performance losses when the data is not in the expected sequence or any keys are missing (the problem grows as the file size increases, as it must re-iterate through the document). And for large, nested objects, simdjson typically requires significantly more coding from the user.
ABC Test shows how simdjson has poor performance when keys are not in the expected sequence:
| Library | Read (MB/s) |
|---|---|
| Glaze | 632 |
| simdjson (on demand) | 107 |
Tagged binary specification: BEVE
| Metric | Roundtrip Time (s) | Write (MB/s) | Read (MB/s) |
|---|---|---|---|
| Raw performance | 0.45 | 3014 | 2062 |
| Equivalent JSON data* | 0.45 | 3292 | 2252 |
JSON message size: 616 bytes
Binary message size: 564 bytes
*Binary data packs more efficiently than JSON, so transporting the same amount of information is even faster.
Actions automatically build and test with Clang, MSVC, and GCC compilers on apple, windows, and linux.
struct my_struct
{
int i = 287;
double d = 3.14;
std::string hello = "Hello World";
std::array<uint64_t, 3> arr = { 1, 2, 3 };
};
template <>
struct glz::meta<my_struct> {
using T = my_struct;
static constexpr auto value = object(
"i", &T::i,
"d", &T::d,
"hello", &T::hello,
"arr", &T::arr
);
};JSON Output/Input
{
"i": 287,
"d": 3.14,
"hello": "Hello World",
"arr": [
1,
2,
3
]
}Write JSON
my_struct s{};
std::string buffer = glz::write_json(s);
// buffer is now: {"i":287,"d":3.14,"hello":"Hello World","arr":[1,2,3]}or
my_struct s{};
std::string buffer{};
glz::write_json(s, buffer);
// buffer is now: {"i":287,"d":3.14,"hello":"Hello World","arr":[1,2,3]}Read JSON
std::string buffer = R"({"i":287,"d":3.14,"hello":"Hello World","arr":[1,2,3]})";
auto s = glz::read_json<my_struct>(buffer);
if (s) // check for error
{
s.value(); // s.value() is a my_struct populated from JSON
}or
std::string buffer = R"({"i":287,"d":3.14,"hello":"Hello World","arr":[1,2,3]})";
my_struct s{};
auto ec = glz::read_json(s, buffer);
if (ec) {
// handle error
}
// populates s from JSONauto ec = glz::read_file(obj, "./obj.json", std::string{}); // reads as JSON from the extension
auto ec = glz::read_file_json(obj, "./obj.txt", std::string{}); // reads some text file as JSON
auto ec = glz::write_file(obj, "./obj.json", std::string{}); // writes file based on extension
auto ec = glz::write_file_json(obj, "./obj.txt", std::string{}); // explicit JSON writeinclude(FetchContent)
FetchContent_Declare(
glaze
GIT_REPOSITORY https://github.com/stephenberry/glaze.git
GIT_TAG main
GIT_SHALLOW TRUE
)
FetchContent_MakeAvailable(glaze)
target_link_libraries(${PROJECT_NAME} PRIVATE glaze::glaze)- Glaze Conan recipe
- Also included in Conan Center
find_package(glaze REQUIRED)
target_link_libraries(main PRIVATE glaze::glaze)
See this Example Repository for how to use Glaze in a new project
See Wiki for Frequently Asked Questions
Glaze also supports metadata provided within its associated class:
struct my_struct
{
int i = 287;
double d = 3.14;
std::string hello = "Hello World";
std::array<uint64_t, 3> arr = { 1, 2, 3 };
struct glaze {
using T = my_struct;
static constexpr auto value = glz::object(
"i", &T::i,
"d", &T::d,
"hello", &T::hello,
"arr", &T::arr
);
};
};Template specialization of
glz::metais preferred when separating class definition from the serialization mapping. Local glaze metadata is helpful for working within the local namespace.
Glaze provides macros to more efficiently register your C++ structs.
Macros must be explicitly included via: #include "glaze/core/macros.hpp"
- GLZ_META is for external registration
- GLZ_LOCAL_META is for internal registration
struct macro_t {
double x = 5.0;
std::string y = "yay!";
int z = 55;
};
GLZ_META(macro_t, x, y, z);
struct local_macro_t {
double x = 5.0;
std::string y = "yay!";
int z = 55;
GLZ_LOCAL_META(local_macro_t, x, y, z);
};Custom reading and writing can be achieved through the powerful to_json/from_json specialization approach, which is described here: custom-serialization.md. However, this only works for user defined types.
For common use cases or cases where a specific member variable should have special reading and writing, you can use glz::custom to register read/write member functions, std::functions, or lambda functions.
See an example:
struct custom_encoding
{
uint64_t x{};
std::string y{};
std::array<uint32_t, 3> z{};
void read_x(const std::string& s) {
x = std::stoi(s);
}
uint64_t write_x() {
return x;
}
void read_y(const std::string& s) {
y = "hello" + s;
}
auto& write_z() {
z[0] = 5;
return z;
}
};
template <>
struct glz::meta<custom_encoding>
{
using T = custom_encoding;
static constexpr auto value = object("x", custom<&T::read_x, &T::write_x>, //
"y", custom<&T::read_y, &T::y>, //
"z", custom<&T::z, &T::write_z>);
};
suite custom_encoding_test = [] {
"custom_reading"_test = [] {
custom_encoding obj{};
std::string s = R"({"x":"3","y":"world","z":[1,2,3]})";
expect(!glz::read_json(obj, s));
expect(obj.x == 3);
expect(obj.y == "helloworld");
expect(obj.z == std::array<uint32_t, 3>{1, 2, 3});
};
"custom_writing"_test = [] {
custom_encoding obj{};
std::string s = R"({"x":"3","y":"world","z":[1,2,3]})";
expect(!glz::read_json(obj, s));
std::string out{};
glz::write_json(obj, out);
expect(out == R"({"x":3,"y":"helloworld","z":[5,2,3]})");
};
};Link to simple JSON pointer syntax explanation
Glaze supports JSON pointer syntax access in a C++ context. This is extremely helpful for building generic APIs, which allows components of complex arguments to be accessed without needed know the encapsulating class.
my_struct s{};
auto d = glz::get<double>(s, "/d");
// d.value() is a std::reference_wrapper to d in the structure smy_struct s{};
glz::set(s, "/d", 42.0);
// d is now 42.0JSON pointer syntax works with deeply nested objects and anything serializable.
// Tuple Example
auto tuple = std::make_tuple(3, 2.7, std::string("curry"));
glz::set(tuple, "/0", 5);
expect(std::get<0>(tuple) == 5.0);read_as allows you to read into an object from a JSON pointer and an input buffer.
Thing thing{};
glz::read_as_json(thing, "/vec3", "[7.6, 1292.1, 0.333]");
expect(thing.vec3.x == 7.6 && thing.vec3.y == 1292.1 &&
thing.vec3.z == 0.333);
glz::read_as_json(thing, "/vec3/2", "999.9");
expect(thing.vec3.z == 999.9);get_as_json allows you to get a targeted value from within an input buffer. This is especially useful if you need to change how an object is parsed based on a value within the object.
std::string s = R"({"obj":{"x":5.5}})";
auto z = glz::get_as_json<double, "/obj/x">(s);
expect(z == 5.5);get_sv_json allows you to get a std::string_view to a targeted value within an input buffer. This can be more efficient to check values and handle custom parsing than constructing a new value with get_as_json.
std::string s = R"({"obj":{"x":5.5}})";
auto view = glz::get_sv_json<"/obj/x">(s);
expect(view == "5.5");Comments are supported with the specification defined here: JSONC
Comments may also be included in the glaze::meta description for your types. These comments can be written out to provide a description of your JSON interface. Calling write_jsonc as opposed to write_json will write out any comments included in the meta description.
struct thing {
double x{5.0};
int y{7};
};
template <>
struct glz::meta<thing> {
using T = thing;
static constexpr auto value = object(
"x", &T::x, "x is a double",
"y", &T::y, "y is an int"
);
};Prettified output:
{
"x": 5 /*x is a double*/,
"y": 7 /*y is an int*/
}When using member pointers (e.g. &T::a) the C++ class structures must match the JSON interface. It may be desirable to map C++ classes with differing layouts to the same object interface. This is accomplished through registering lambda functions instead of member pointers.
template <>
struct glz::meta<Thing> {
static constexpr auto value = object(
"i", [](auto&& self) -> auto& { return self.subclass.i; }
);
};The value self passed to the lambda function will be a Thing object, and the lambda function allows us to make the subclass invisible to the object interface.
Lambda functions by default copy returns, therefore the auto& return type is typically required in order for glaze to write to memory.
Note that remapping can also be achieved through pointers/references, as glaze treats values, pointers, and references in the same manner when writing/reading.
By default enums will be written and read in integer form. No glz::meta is necessary if this is the desired behavior.
However, if you prefer to use enums as strings in JSON, they can be registered in the glz::meta as follows:
enum class Color { Red, Green, Blue };
template <>
struct glz::meta<Color> {
using enum Color;
static constexpr auto value = enumerate("Red", Red,
"Green", Green,
"Blue", Blue
);
};In use:
Color color = Color::Red;
std::string buffer{};
glz::write_json(color, buffer);
expect(buffer == "\"Red\"");Formatted JSON can be written out directly via a compile time option:
glz::write<glz::opts{.prettify = true}>(obj, buffer);Or, JSON text can be formatted with the glz::prettify function:
std::string buffer = R"({"i":287,"d":3.14,"hello":"Hello World","arr":[1,2,3]})");
auto beautiful = glz::prettify(buffer);beautiful is now:
{
"i": 287,
"d": 3.14,
"hello": "Hello World",
"arr": [
1,
2,
3
]
}Simplified prettify definition below, which allows the use of tabs or changing the number of spaces per indent.
string prettify(auto& in, bool tabs = false, uint32_t indent_size = 3)Array types logically convert to JSON array values. Concepts are used to allow various containers and even user containers if they match standard library interfaces.
glz::array(compile time mixed types)std::tuplestd::arraystd::vectorstd::dequestd::liststd::forward_liststd::spanstd::setstd::unordered_set
Object types logically convert to JSON object values, such as maps. Like JSON, Glaze treats object definitions as unordered maps. Therefore the order of an object layout does not have to mach the same binary sequence in C++ (hence the tagged specification).
glz::object(compile time mixed types)std::mapstd::unordered_map
Glaze supports std::unique_ptr, std::shared_ptr, and std::optional as nullable types. Nullable types can be allocated by JSON input or nullified by the null keyword.
std::unique_ptr<int> ptr{};
std::string buffer{};
glz::write_json(ptr, buffer);
expect(buffer == "null");
glz::read_json(ptr, "5");
expect(*ptr == 5);
buffer.clear();
glz::write_json(ptr, buffer);
expect(buffer == "5");
glz::read_json(ptr, "null");
expect(!bool(ptr));A class can be treated as an underlying value as follows:
struct S {
int x{};
};
template <>
struct glz::meta<S> {
static constexpr auto value{ &S::x };
};or using a lambda:
template <>
struct glz::meta<S> {
static constexpr auto value = [](auto& self) -> auto& { return self.x; };
};Glaze supports registering a set of boolean flags that behave as an array of string options:
struct flags_t {
bool x{ true };
bool y{};
bool z{ true };
};
template <>
struct glz::meta<flags_t> {
using T = flags_t;
static constexpr auto value = flags("x", &T::x, "y", &T::y, "z", &T::z);
};Example:
flags_t s{};
expect(glz::write_json(s) == R"(["x","z"])");Only "x" and "z" are written out, because they are true. Reading in the buffer will set the appropriate booleans.
When writing binary,
flagsonly uses one bit per boolean (byte aligned).
See Variant Handling for details on std::variant support.
Sometimes you just want to write out JSON structures on the fly as efficiently as possible. Glaze provides tuple-like structures that allow you to stack allocate structures to write out JSON with high speed. These structures are named glz::obj for objects and glz::arr for arrays.
Below is an example of building an object, which also contains an array, and writing it out.
auto obj = glz::obj{"pi", 3.14, "happy", true, "name", "Stephen", "arr", glz::arr{"Hello", "World", 2}};
std::string s{};
glz::write_json(obj, s);
expect(s == R"({"pi":3.14,"happy":true,"name":"Stephen","arr":["Hello","World",2]})");This approach is significantly faster than
glz::json_tfor generic JSON. But, may not be suitable for all contexts.
glz::merge allows the user to merge multiple JSON object types into a single object.
glz::obj o{"pi", 3.141};
std::map<std::string_view, int> map = {{"a", 1}, {"b", 2}, {"c", 3}};
auto merged = glz::merge{o, map};
std::string s{};
glz::write_json(merged, s); // will write out a single, merged object
// s is now: {"pi":3.141,"a":0,"b":2,"c":3}
glz::mergestores references to lvalues to avoid copies
See Generic JSON for glz::json_t.
glz::json_t json{};
std::string buffer = R"([5,"Hello World",{"pi":3.14}])";
glz::read_json(json, buffer);
assert(json[2]["pi"].get<double>() == 3.14);Glaze is safe to use with untrusted messages. Errors are returned as error codes, typically within a glz::expected, which behaves just like a std::expected.
To generate more helpful error messages, call format_error:
auto pe = glz::read_json(obj, buffer);
if (pe) {
std::string descriptive_error = glz::format_error(pe, s);
}This test case:
{"Hello":"World"x, "color": "red"}Produces this error:
1:17: syntax_error
{"Hello":"World"x, "color": "red"}
^
Denoting that x is invalid here.
Glaze is just about as fast writing to a std::string as it is writing to a raw char buffer. If you have sufficiently allocated space in your buffer you can write to the raw buffer, as shown below, but it is not recommended.
glz::read_json(obj, buffer);
const auto n = glz::write_json(obj, buffer.data());
buffer.resize(n);
The glz::opts struct defines compile time optional settings for reading/writing.
Instead of calling glz::read_json(...), you can call glz::read<glz::opts{}>(...) and customize the options.
For example: glz::read<glz::opts{.error_on_unknown_keys = false}>(...) will turn off erroring on unknown keys and simple skip the items.
glz::opts can also switch between formats:
glz::read<glz::opts{.format = glz::binary}>(...)->glz::read_binary(...)glz::read<glz::opts{.format = glz::json}>(...)->glz::read_json(...)
The struct below shows the available options and the default behavior.
struct opts {
uint32_t format = json;
bool comments = false; // Write out comments
bool error_on_unknown_keys = true; // Error when an unknown key is encountered
bool skip_null_members = true; // Skip writing out params in an object if the value is null
bool use_hash_comparison = true; // Will replace some string equality checks with hash checks
bool prettify = false; // Write out prettified JSON
char indentation_char = ' '; // Prettified JSON indentation char
uint8_t indentation_width = 3; // Prettified JSON indentation size
bool shrink_to_fit = false; // Shrinks dynamic containers to new size to save memory
bool write_type_info = true; // Write type info for meta objects in variants
bool force_conformance = false; // Do not allow invalid json normally accepted such as comments, nan, inf.
bool error_on_missing_keys = false; // Require all non nullable keys to be present in the object. Use
// skip_null_members = false to require nullable members
uint32_t layout = rowwise; // CSV row wise output/input
bool quoted_num = false; // treat numbers as quoted or array-like types as having quoted numbers
bool number = false; // read numbers as strings and write these string as numbers
};It can be useful to acknowledge a keys existence in an object to prevent errors, and yet the value may not be needed or exist in C++. These cases are handled by registering a glz::skip type with the meta data.
struct S {
int i{};
};
template <>
struct glz::meta<S> {
static constexpr auto value = object("key_to_skip", skip{}, "x", &S::i);
};std::string buffer = R"({"key_to_skip": [1,2,3], "i": 7})";
S s{};
glz::read_json(s, buffer);
// The value [1,2,3] will be skipped
expect(s.i == 7); // only the value i will be read intoGlaze is designed to help with building generic APIs. Sometimes a value needs to be exposed to the API, but it is not desirable to read in or write out the value in JSON. This is the use case for glz::hide.
glz::hide hides the value from JSON output while still allowing API access.
struct hide_struct {
int i = 287;
double d = 3.14;
std::string hello = "Hello World";
};
template <>
struct glz::meta<hide_struct> {
using T = hide_struct;
static constexpr auto value = object("i", &T::i, //
"d", &T::d, //
"hello", hide{&T::hello});
};hide_struct s{};
auto b = glz::write_json(s);
expect(b == R"({"i":287,"d":3.14})"); // notice that "hello" is hidden from the outputYou can parse quoted JSON numbers directly to types like double, int, etc. by utilizing the glz::quoted wrapper.
struct A {
double x;
std::vector<uint32_t> y;
};
template <>
struct glz::meta<A> {
static constexpr auto value = object("x", glz::quoted_num<&A::x>, "y", glz::quoted_num<&A::y>;
};{
"x": "3.14",
"y": ["1", "2", "3"]
}The quoted JSON numbers will be parsed directly into the double and std::vector<uint32_t>. The glz::quoted function works for nested objects and arrays as well.
Glaze supports Newline Delimited JSON for array-like types (e.g. std::vector and std::tuple).
std::vector<std::string> x = { "Hello", "World", "Ice", "Cream" };
std::string s = glz::write_ndjson(x);
glz::read_ndjson(x, s);See the ext directory for extensions.
- Eigen. Supports reading and writing from Eigen Vector types.
- JSON-RPC documentation. Glaze wrapper supporting JSON-RPC 2.0 specification.
Glaze is distributed under the MIT license with an exception for embedded forms:
--- Optional exception to the license ---
As an exception, if, as a result of your compiling your source code, portions of this Software are embedded into a machine-executable object form of such source code, you may redistribute such embedded portions in such object form without including the copyright and permission notices.