56 lines
1.2 KiB
Markdown
56 lines
1.2 KiB
Markdown
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# nlohmann::basic_json::empty
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```cpp
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bool empty() const noexcept;
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```
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Checks if the container has no elements; that is, whether `begin() == end()`.
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## Parameters
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(none)
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## Return value
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`true` if the container is empty, `false` otherwise. Note that the JSON types string, number, and boolean are never empty, null values are always empty.
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## Exceptions
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`noexcept` specification: `noexcept`.
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## Complexity
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Constant (assuming types `ObjectType` and `ArrayType` satisfy the [Container](http://en.cppreference.com/w/cpp/concept/Container) concept).
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## Example
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The following code uses empty to check if a `json` container contains any elements:
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```cpp
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#include <json.hpp>
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#include <iostream>
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int main()
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{
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nlohman::json numbers;
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std::cout << "Initially, numbers.empty(): " << numbers.empty() << '\n';
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numbers.push_back(42);
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numbers.push_back(13317);
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std::cout << "After adding elements, numbers.empty(): " << numbers.empty() << '\n';
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}
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```
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### Output
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Initially, numbers.empty(): 1
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After adding elements, numbers.empty(): 0
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## Requirements
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The `empty` member function is part of the [Container](http://en.cppreference.com/w/cpp/concept/Container) requirement.
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## See also
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- `size()`
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