JSON for Modern C++  2.0.0
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>
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
std::out_of_rangeif the JSON pointer can not be resolved
std::domain_errorif an array index begins with '0'
std::invalid_argumentif an array index was not a number
Example
The behavior is shown in the example.
1 #include <json.hpp>
2 
3 using json = nlohmann::json;
4 
5 int main()
6 {
7  // create a JSON value
8  const json j =
9  {
10  {"number", 1}, {"string", "foo"}, {"array", {1, 2}}
11  };
12 
13  // read-only access
14 
15  // output element with JSON pointer "/number"
16  std::cout << j["/number"_json_pointer] << '\n';
17  // output element with JSON pointer "/string"
18  std::cout << j["/string"_json_pointer] << '\n';
19  // output element with JSON pointer "/array"
20  std::cout << j["/array"_json_pointer] << '\n';
21  // output element with JSON pointer "/array/1"
22  std::cout << j["/array/1"_json_pointer] << '\n';
23 }
basic_json<> json
default JSON class
Definition: json.hpp:9587
Output (play with this example online):
1
"foo"
[1,2]
2
The example code above can be translated with
g++ -std=c++11 -Isrc doc/examples/operatorjson_pointer_const.cpp -o operatorjson_pointer_const 
Since
version 2.0.0

Definition at line 8985 of file json.hpp.