nlohmann::ordered_map

template<class Key, class T, class IgnoredLess = std::less<Key>,
         class Allocator = std::allocator<std::pair<const Key, T>>>
struct ordered_map : std::vector<std::pair<const Key, T>, Allocator>;

A minimal map-like container that preserves insertion order for use within nlohmann::ordered_json (nlohmann::basic_json<ordered_map>).

Template parameters

Key: key type
T: mapped type
IgnoredLess: comparison function (ignored and only added to ensure compatibility with #!cpp std::map)
Allocator: allocator type

Iterator invalidation

The type uses a std::vector to store object elements. Therefore, adding elements can yield a reallocation in which case all iterators (including the end() iterator) and all references to the elements are invalidated.

Member types

key_type - key type (Key)
mapped_type - mapped type (T)
Container - base container type (#!cpp std::vector<std::pair<const Key, T>, Allocator>)
iterator
const_iterator
size_type
value_type
key_compare - key comparison function

std::equal_to<Key>  // until C++14

std::equal_to<>     // since C++14

Member functions

(constructor)
(destructor)
emplace
operator[]
at
erase
count
find
insert

Examples

??? example

The example shows the different behavior of `std::map` and `nlohmann::ordered_map`.
 
```cpp
--8<-- "examples/ordered_map.cpp"
```

Output:

```json
--8<-- "examples/ordered_map.output"
```

Version history

Added in version 3.9.0 to implement nlohmann::ordered_json.
Added key_compare member in version 3.11.0.

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