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api/basic_json/std_hash/index.md

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+# std::hash<nlohmann::basic_json>
+
+```
+namespace std {
+    struct hash<nlohmann::basic_json>;
+}
+```
+
+Return a hash value for a JSON object. The hash function tries to rely on `std::hash` where possible. Furthermore, the type of the JSON value is taken into account to have different hash values for `null`, `0`, `0U`, and `false`, etc.
+
+## Examples
+
+Example
+
+The example shows how to calculate hash values for different JSON values.
+
+```
+#include <iostream>
+#include <iomanip>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+using namespace nlohmann::literals;
+
+int main()
+{
+    std::cout << "hash(null) = " << std::hash<json> {}(json(nullptr)) << '\n'
+              << "hash(false) = " << std::hash<json> {}(json(false)) << '\n'
+              << "hash(0) = " << std::hash<json> {}(json(0)) << '\n'
+              << "hash(0U) = " << std::hash<json> {}(json(0U)) << '\n'
+              << "hash(\"\") = " << std::hash<json> {}(json("")) << '\n'
+              << "hash({}) = " << std::hash<json> {}(json::object()) << '\n'
+              << "hash([]) = " << std::hash<json> {}(json::array()) << '\n'
+              << "hash({\"hello\": \"world\"}) = " << std::hash<json> {}("{\"hello\": \"world\"}"_json)
+              << std::endl;
+}
+```
+
+Output:
+
+```
+hash(null) = 2654435769
+hash(false) = 2654436030
+hash(0) = 2654436095
+hash(0U) = 2654436156
+hash("") = 6142509191626859748
+hash({}) = 2654435832
+hash([]) = 2654435899
+hash({"hello": "world"}) = 4469488738203676328
+```
+
+Note the output is platform-dependent.
+
+## Version history
+
+- Added in version 1.0.0.
+- Extended for arbitrary basic_json types in version 3.10.5.