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2026-07-09 12:05:10 +00:00 · 2026-07-08 18:19:46 +00:00
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+# nlohmann::basic_json::value_t
+
+```
+enum class value_t : std::uint8_t {
+    null,
+    object,
+    array,
+    string,
+    boolean,
+    number_integer,
+    number_unsigned,
+    number_float,
+    binary,
+    discarded
+};
+```
+
+This enumeration collects the different JSON types. It is internally used to distinguish the stored values, and the functions [`is_null`](https://json.nlohmann.me/api/basic_json/is_null/index.md), [`is_object`](https://json.nlohmann.me/api/basic_json/is_object/index.md), [`is_array`](https://json.nlohmann.me/api/basic_json/is_array/index.md), [`is_string`](https://json.nlohmann.me/api/basic_json/is_string/index.md), [`is_boolean`](https://json.nlohmann.me/api/basic_json/is_boolean/index.md), [`is_number`](https://json.nlohmann.me/api/basic_json/is_number/index.md) (with [`is_number_integer`](https://json.nlohmann.me/api/basic_json/is_number_integer/index.md), [`is_number_unsigned`](https://json.nlohmann.me/api/basic_json/is_number_unsigned/index.md), and [`is_number_float`](https://json.nlohmann.me/api/basic_json/is_number_float/index.md)), [`is_discarded`](https://json.nlohmann.me/api/basic_json/is_discarded/index.md), [`is_binary`](https://json.nlohmann.me/api/basic_json/is_binary/index.md), [`is_primitive`](https://json.nlohmann.me/api/basic_json/is_primitive/index.md), and [`is_structured`](https://json.nlohmann.me/api/basic_json/is_structured/index.md) rely on it.
+
+## Notes
+
+Ordering
+
+The order of types is as follows:
+
+1. `null`
+1. `boolean`
+1. `number_integer`, `number_unsigned`, `number_float`
+1. `object`
+1. `array`
+1. `string`
+1. `binary`
+
+`discarded` is unordered.
+
+Types of numbers
+
+There are three enumerators for numbers (`number_integer`, `number_unsigned`, and `number_float`) to distinguish between different types of numbers:
+
+- [`number_unsigned_t`](https://json.nlohmann.me/api/basic_json/number_unsigned_t/index.md) for unsigned integers
+- [`number_integer_t`](https://json.nlohmann.me/api/basic_json/number_integer_t/index.md) for signed integers
+- [`number_float_t`](https://json.nlohmann.me/api/basic_json/number_float_t/index.md) for floating-point numbers or to approximate integers which do not fit into the limits of their respective type
+
+Comparison operators
+
+`operator<` and `operator<=>` (since C++20) are overloaded and compare according to the ordering described above. Until C++20 all other relational and equality operators yield results according to the integer value of each enumerator. Since C++20 some compilers consider the *rewritten candidates* generated from `operator<=>` during overload resolution, while others do not. For predictable and portable behavior use:
+
+- `operator<` or `operator<=>` when wanting to compare according to the order described above
+- `operator==` or `operator!=` when wanting to compare according to each enumerators integer value
+
+## Examples
+
+Example
+
+The following code how `type()` queries the `value_t` for all JSON types.
+
+```
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // create JSON values
+    json j_null;
+    json j_boolean = true;
+    json j_number_integer = -17;
+    json j_number_unsigned = 42u;
+    json j_number_float = 23.42;
+    json j_object = {{"one", 1}, {"two", 2}};
+    json j_array = {1, 2, 4, 8, 16};
+    json j_string = "Hello, world";
+
+    // call type()
+    std::cout << std::boolalpha;
+    std::cout << (j_null.type() == json::value_t::null) << '\n';
+    std::cout << (j_boolean.type() == json::value_t::boolean) << '\n';
+    std::cout << (j_number_integer.type() == json::value_t::number_integer) << '\n';
+    std::cout << (j_number_unsigned.type() == json::value_t::number_unsigned) << '\n';
+    std::cout << (j_number_float.type() == json::value_t::number_float) << '\n';
+    std::cout << (j_object.type() == json::value_t::object) << '\n';
+    std::cout << (j_array.type() == json::value_t::array) << '\n';
+    std::cout << (j_string.type() == json::value_t::string) << '\n';
+}
+```
+
+Output:
+
+```
+true
+true
+true
+true
+true
+true
+true
+true
+```
+
+## Version history
+
+- Added in version 1.0.0.
+- Added unsigned integer type in version 2.0.0.
+- Added binary type in version 3.8.0.