JSON for Modern C++  3.7.0

◆ 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::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
Linear in the size the JSON value.
Exceptions
type_error.314if value is not an object
type_error.315if object values are not primitive
Example
The following code shows how a flattened JSON object is unflattened into the original nested JSON object.
1 #include <iostream>
2 #include <iomanip>
3 #include <nlohmann/json.hpp>
4 
5 using json = nlohmann::json;
6 
7 int main()
8 {
9  // create JSON value
10  json j_flattened =
11  {
12  {"/answer/everything", 42},
13  {"/happy", true},
14  {"/list/0", 1},
15  {"/list/1", 0},
16  {"/list/2", 2},
17  {"/name", "Niels"},
18  {"/nothing", nullptr},
19  {"/object/currency", "USD"},
20  {"/object/value", 42.99},
21  {"/pi", 3.141}
22  };
23 
24  // call unflatten()
25  std::cout << std::setw(4) << j_flattened.unflatten() << '\n';
26 }
basic_json<> json
default JSON class
Definition: json.hpp:2355

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 -Isingle_include doc/examples/unflatten.cpp -o unflatten 
See also
flatten() for the reverse function
Since
version 2.0.0

Definition at line 21875 of file json.hpp.