JSON for Modern C++ 2.1.1
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◆ unflatten()

template<template< typename U, typename V, typename... Args > class ObjectType = std::map, template< typename U, typename... Args > class ArrayType = std::vector, class StringType = std::string, class BooleanType = bool, class NumberIntegerType = std::int64_t, class NumberUnsignedType = std::uint64_t, class NumberFloatType = double, template< typename U > class AllocatorType = std::allocator, template< typename T, typename SFINAE=void > class JSONSerializer = adl_serializer>
basic_json nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::unflatten ( ) const
inline

The function restores the arbitrary nesting of a JSON value that has been flattened before using the flatten() function. The JSON value must meet certain constraints:

  1. The value must be an object.
  2. The keys must be JSON pointers (see RFC 6901)
  3. The mapped values must be primitive JSON types.
Returns
the original JSON from a flattened version
Note
Empty objects and arrays are flattened by flatten() to null values and can not unflattened to their original type. Apart from this example, for a JSON value j, the following is always true: j == j.flatten().unflatten().
Complexity\n Linear in the size the JSON value.
Example\n The following code shows how a flattened JSON object is
unflattened into the original nested JSON object.
1#include <json.hpp>
2
3using json = nlohmann::json;
4
5int main()
6{
7 // create JSON value
9 {
10 {"/answer/everything", 42},
11 {"/happy", true},
12 {"/list/0", 1},
13 {"/list/1", 0},
14 {"/list/2", 2},
15 {"/name", "Niels"},
16 {"/nothing", nullptr},
17 {"/object/currency", "USD"},
18 {"/object/value", 42.99},
19 {"/pi", 3.141}
20 };
21
22 // call unflatten()
23 std::cout << std::setw(4) << j_flattened.unflatten() << '\n';
24}
static basic_json array(std::initializer_list< basic_json > init=std::initializer_list< basic_json >())
explicitly create an array from an initializer list
Definition json.hpp:2165
basic_json unflatten() const
unflatten a previously flattened JSON value
Definition json.hpp:11879
a class to store JSON values
Definition json.hpp:1040
basic_json<> json
default JSON class
Definition json.hpp:12369

Output (play with this example online):
{
    "answer": {
        "everything": 42
    },
    "happy": true,
    "list": [
        1,
        0,
        2
    ],
    "name": "Niels",
    "nothing": null,
    "object": {
        "currency": "USD",
        "value": 42.99
    },
    "pi": 3.141
}

The example code above can be translated with
g++ -std=c++11 -Isrc doc/examples/unflatten.cpp -o unflatten 
See also
flatten() for the reverse function
Since
version 2.0.0

Definition at line 11879 of file json.hpp.