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106 lines
2.6 KiB
Markdown
106 lines
2.6 KiB
Markdown
# <small>nlohmann::basic_json::</small>clear
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```cpp
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void clear() noexcept;
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```
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Clears the content of a JSON value and resets it to the default value as if [`basic_json(value_t)`](basic_json.md) would
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have been called with the current value type from [`type()`](type.md):
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| Value type | initial value |
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|------------|-----------------------------------------|
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| null | `null` |
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| boolean | `false` |
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| string | `""` |
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| number | `0` |
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| binary | An empty byte vector with no subtype |
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| object | `{}` |
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| array | `[]` |
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Has the same effect as calling
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```.cpp
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*this = basic_json(type());
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```
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## Exception safety
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No-throw guarantee: this function never throws exceptions.
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## Complexity
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Linear in the size of the JSON value.
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## Notes
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All iterators, pointers, and references related to this container are invalidated.
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## Examples
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??? example
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The example below shows the effect of `clear()` to different
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JSON types.
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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 JSON values
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json j_null;
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json j_boolean = true;
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json j_number_integer = 17;
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json j_number_float = 23.42;
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json j_object = {{"one", 1}, {"two", 2}};
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json j_array = {1, 2, 4, 8, 16};
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json j_string = "Hello, world";
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// call clear()
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j_null.clear();
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j_boolean.clear();
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j_number_integer.clear();
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j_number_float.clear();
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j_object.clear();
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j_array.clear();
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j_string.clear();
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// serialize the cleared values()
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std::cout << j_null << '\n';
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std::cout << j_boolean << '\n';
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std::cout << j_number_integer << '\n';
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std::cout << j_number_float << '\n';
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std::cout << j_object << '\n';
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std::cout << j_array << '\n';
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std::cout << j_string << '\n';
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}
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```
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Output:
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```json
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null
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false
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0
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0.0
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{}
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[]
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""
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```
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## See also
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- [erase](erase.md) removes elements from a JSON value
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- [empty](empty.md) checks whether the JSON value has no elements
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## Version history
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- Added in version 1.0.0.
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- Added support for binary types in version 3.8.0.
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- Fixed in version 3.13.0 to also clear the subtype of a binary value; before, the subtype was left unchanged.
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