79 lines
1.8 KiB
Markdown
79 lines
1.8 KiB
Markdown
# <small>nlohmann::adl_serializer::</small>to_json
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```cpp
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template<typename BasicJsonType, typename TargetType = ValueType>
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static auto to_json(BasicJsonType& j, TargetType && val) noexcept(
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noexcept(::nlohmann::to_json(j, std::forward<TargetType>(val))))
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-> decltype(::nlohmann::to_json(j, std::forward<TargetType>(val)), void())
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```
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This function is usually called by the constructors of the [basic_json](../basic_json/index.md) class.
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## Parameters
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`j` (out)
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: JSON value to write to
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`val` (in)
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: value to read from
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## Examples
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??? example
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The example below shows how a `to_json` function can be implemented for a user-defined type. This function is called
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by the `adl_serializer` when the constructor `basic_json(ns::person)` is called.
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```cpp
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#include <iostream>
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#include <nlohmann/json.hpp>
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using nlohmann::json;
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namespace ns
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{
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// a simple struct to model a person
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struct person
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{
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std::string name;
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std::string address;
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int age;
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};
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} // namespace ns
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namespace ns
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{
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void to_json(json& j, const person& p)
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{
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j = json{ {"name", p.name}, {"address", p.address}, {"age", p.age} };
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}
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} // namespace ns
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int main()
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{
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ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};
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json j = p;
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std::cout << j << '\n';
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}
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```
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Output:
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```json
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{"address":"744 Evergreen Terrace","age":60,"name":"Ned Flanders"}
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```
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## See also
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- [`from_json`](from_json.md) - convert JSON to a C++ value
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- [Arbitrary Type Conversions](../../features/arbitrary_types.md) - write your own `from_json` and `to_json` functions
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- [Converting values](../../features/conversions.md) - overview of `get`, `get_to` and implicit conversions
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## Version history
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- Added in version 2.1.0.
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