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67 lines
1.7 KiB
Markdown
67 lines
1.7 KiB
Markdown
# <small>nlohmann::basic_json::</small>empty
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```cpp
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bool empty() const noexcept;
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```
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Checks if a JSON value has no elements (i.e. whether its [`size()`](size.md) is `0`).
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## Return value
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The return value depends on the different types and is defined as follows:
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| Value type | return value |
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|------------|----------------------------------------|
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| null | `#!cpp true` |
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| boolean | `#!cpp false` |
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| string | `#!cpp false` |
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| number | `#!cpp false` |
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| binary | `#!cpp false` |
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| object | result of function `object_t::empty()` |
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| array | result of function `array_t::empty()` |
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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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Constant, as long as [`array_t`](array_t.md) and [`object_t`](object_t.md) satisfy the
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[Container](https://en.cppreference.com/w/cpp/named_req/Container) concept; that is, their `empty()` functions have
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constant complexity.
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## Possible implementation
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```cpp
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bool empty() const noexcept
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{
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return size() == 0;
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}
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```
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## Notes
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This function does not return whether a string stored as JSON value is empty -- it returns whether the JSON container
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itself is empty which is `#!cpp false` in the case of a string.
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## Examples
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??? example
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The following code uses `empty()` to check if a JSON object contains any elements.
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```cpp
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--8<-- "examples/empty.cpp"
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```
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Output:
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```json
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--8<-- "examples/empty.output"
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```
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## Version history
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- Added in version 1.0.0.
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- Extended to return `#!cpp false` for binary types in version 3.8.0.
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