JSON for Modern C++  3.7.0

◆ operator[]() [8/8]

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>
const_reference nlohmann::basic_json::operator[] ( const json_pointer ptr) const
inline

Uses a JSON pointer to retrieve a reference to the respective JSON value. No bound checking is performed. The function does not change the JSON value; no null values are created. In particular, the the special value - yields an exception.

Parameters
[in]ptrJSON pointer to the desired element
Returns
const reference to the element pointed to by ptr
Complexity
Constant.
Exceptions
parse_error.106if an array index begins with '0'
parse_error.109if an array index was not a number
out_of_range.402if the array index '-' is used
out_of_range.404if the JSON pointer can not be resolved
Example
The behavior is shown in the example.
1 #include <iostream>
2 #include <nlohmann/json.hpp>
3 
4 using json = nlohmann::json;
5 
6 int main()
7 {
8  // create a JSON value
9  const json j =
10  {
11  {"number", 1}, {"string", "foo"}, {"array", {1, 2}}
12  };
13 
14  // read-only access
15 
16  // output element with JSON pointer "/number"
17  std::cout << j["/number"_json_pointer] << '\n';
18  // output element with JSON pointer "/string"
19  std::cout << j["/string"_json_pointer] << '\n';
20  // output element with JSON pointer "/array"
21  std::cout << j["/array"_json_pointer] << '\n';
22  // output element with JSON pointer "/array/1"
23  std::cout << j["/array/1"_json_pointer] << '\n';
24 }
basic_json<> json
default JSON class
Definition: json.hpp:2355

Output (play with this example online):
1
"foo"
[1,2]
2
The example code above can be translated with
g++ -std=c++11 -Isingle_include doc/examples/operatorjson_pointer_const.cpp -o operatorjson_pointer_const 
Since
version 2.0.0

Definition at line 21725 of file json.hpp.