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@@ -42,13 +42,32 @@ If you do want to preserve the **insertion order**, you can use the type [`nlohm
??? example "Example: `ordered_json` preserves insertion order"
```cpp
--8<-- "examples/ordered_json.cpp"
#include <iostream>
#include <nlohmann/json.hpp>
using ordered_json = nlohmann::ordered_json;
int main()
{
ordered_json j;
j["one"] = 1;
j["two"] = 2;
j["three"] = 3;
std::cout << j.dump(2) << '\n';
}
```
Output:
```json
--8<-- "examples/ordered_json.output"
{
"one": 1,
"two": 2,
"three": 3
}
```
Alternatively, [`nlohmann::fifo_map`](https://github.com/nlohmann/fifo_map) also preserves the insertion order and, unlike [`ordered_map`](../api/ordered_map.md), keeps a lookup index, so it does not have the quadratic cost described below. It is used through a small adapter ([integration](https://github.com/nlohmann/json/issues/485#issuecomment-333652309)).