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71 lines
1.4 KiB
Markdown
71 lines
1.4 KiB
Markdown
# <small>nlohmann::</small>ordered_map
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```cpp
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template<class Key, class T, class IgnoredLess = std::less<Key>,
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class Allocator = std::allocator<std::pair<const Key, T>>>
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struct ordered_map : std::vector<std::pair<const Key, T>, Allocator>;
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```
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A minimal map-like container that preserves insertion order for use within [`nlohmann::ordered_json`](ordered_json.md)
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(`nlohmann::basic_json<ordered_map>`).
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## Template parameters
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`Key`
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: key type
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`T`
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: mapped type
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`IgnoredLess`
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: comparison function (ignored and only added to ensure compatibility with `#!cpp std::map`)
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`Allocator`
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: allocator type
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## Member types
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- **key_type** - key type (`Key`)
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- **mapped_type** - mapped type (`T`)
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- **Container** - base container type (`#!cpp std::vector<std::pair<const Key, T>, Allocator>`)
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- **iterator**
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- **const_iterator**
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- **size_type**
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- **value_type**
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## Member functions
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- (constructor)
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- (destructor)
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- **emplace**
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- **operator\[\]**
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- **at**
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- **erase**
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- **count**
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- **find**
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- **insert**
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## Examples
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??? example
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The example shows the different behavior of `std::map` and `nlohmann::ordered_map`.
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```cpp
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--8<-- "examples/ordered_map.cpp"
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```
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Output:
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```json
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--8<-- "examples/ordered_map.output"
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```
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## See also
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- [ordered_json](ordered_json.md)
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## Version history
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- Added in version 3.9.0 to implement [`nlohmann::ordered_json`](ordered_json.md).
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