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98 lines
2.4 KiB
Markdown
98 lines
2.4 KiB
Markdown
# <small>nlohmann::basic_json::</small>get_ref
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```cpp
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template<typename ReferenceType>
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ReferenceType get_ref();
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template<typename ReferenceType>
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const ReferenceType get_ref() const;
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```
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Implicit reference access to the internally stored JSON value. No copies are made.
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## Template parameters
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`ReferenceType`
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: reference type; must be a reference to [`array_t`](array_t.md), [`object_t`](object_t.md),
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[`string_t`](string_t.md), [`boolean_t`](boolean_t.md), [`number_integer_t`](number_integer_t.md), or
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[`number_unsigned_t`](number_unsigned_t.md), [`number_float_t`](number_float_t.md), or [`binary_t`](binary_t.md).
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Enforced by a static assertion.
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## Return value
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reference to the internally stored JSON value if the requested reference type fits to the JSON value; throws
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[`type_error.303`](../../home/exceptions.md#jsonexceptiontype_error303) otherwise
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## Exception safety
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Strong exception safety: if an exception occurs, the original value stays intact.
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## Exceptions
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Throws [`type_error.303`](../../home/exceptions.md#jsonexceptiontype_error303) if the requested reference type does not
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match the stored JSON value type; example: `"incompatible ReferenceType for get_ref, actual type is binary"`.
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## Complexity
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Constant.
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## Notes
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!!! danger "Undefined behavior"
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The reference becomes invalid if the underlying JSON object changes.
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## Examples
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??? example
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The example shows several calls to `get_ref()`.
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```cpp
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#include <iostream>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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int main()
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{
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// create a JSON number
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json value = 17;
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// explicitly getting references
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auto r1 = value.get_ref<const json::number_integer_t&>();
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auto r2 = value.get_ref<json::number_integer_t&>();
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// print the values
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std::cout << r1 << ' ' << r2 << '\n';
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// incompatible type throws exception
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try
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{
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auto r3 = value.get_ref<json::number_float_t&>();
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}
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catch (const json::type_error& ex)
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{
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std::cout << ex.what() << '\n';
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}
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}
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```
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Output:
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```json
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17 17
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[json.exception.type_error.303] incompatible ReferenceType for get_ref, actual type is number
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```
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## See also
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- [get_ptr()](get_ptr.md) get a pointer value
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## Version history
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- Added in version 1.1.0.
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- Extended to binary types in version 3.8.0.
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