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nlohmann
58 lines
1.6 KiB
Markdown
58 lines
1.6 KiB
Markdown
# std::hash<nlohmann::basic_json>
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```
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namespace std {
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struct hash<nlohmann::basic_json>;
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}
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```
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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.
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## Examples
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Example
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The example shows how to calculate hash values for different JSON values.
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```
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#include <iostream>
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#include <iomanip>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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using namespace nlohmann::literals;
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int main()
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{
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std::cout << "hash(null) = " << std::hash<json> {}(json(nullptr)) << '\n'
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<< "hash(false) = " << std::hash<json> {}(json(false)) << '\n'
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<< "hash(0) = " << std::hash<json> {}(json(0)) << '\n'
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<< "hash(0U) = " << std::hash<json> {}(json(0U)) << '\n'
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<< "hash(\"\") = " << std::hash<json> {}(json("")) << '\n'
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<< "hash({}) = " << std::hash<json> {}(json::object()) << '\n'
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<< "hash([]) = " << std::hash<json> {}(json::array()) << '\n'
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<< "hash({\"hello\": \"world\"}) = " << std::hash<json> {}("{\"hello\": \"world\"}"_json)
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<< std::endl;
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}
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```
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Output:
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```
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hash(null) = 2654435769
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hash(false) = 2654436030
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hash(0) = 2654436095
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hash(0U) = 2654436156
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hash("") = 6142509191626859748
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hash({}) = 2654435832
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hash([]) = 2654435899
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hash({"hello": "world"}) = 4469488738203676328
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```
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Note the output is platform-dependent.
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## Version history
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- Added in version 1.0.0.
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- Extended for arbitrary basic_json types in version 3.10.5.
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