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"
```

See also

Version history