JSON for Modern C++  3.5.0

◆ operator[]() [7/8]

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

Uses a JSON pointer to retrieve a reference to the respective JSON value. No bound checking is performed. Similar to operator[](const typename object_t::key_type&), null values are created in arrays and objects if necessary.

In particular:

  • If the JSON pointer points to an object key that does not exist, it is created an filled with a null value before a reference to it is returned.
  • If the JSON pointer points to an array index that does not exist, it is created an filled with a null value before a reference to it is returned. All indices between the current maximum and the given index are also filled with null.
  • The special value - is treated as a synonym for the index past the end.
Parameters
[in]ptra JSON pointer
Returns
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.404if the JSON pointer can not be resolved
Example^^ The behavior is shown in the example. ^^ operatorjson_pointer.cpp
Output (play with this example online):^^
1
"foo"
[1,2]
2
"bar"
{"array":[1,2],"boolean":true,"number":1,"string":"bar"}
[1,21,null,null,44]
[1,21,null,null,44,55]
^^ The example code above can be translated with
g++ -std=c++11 -Isingle_include doc/examples/operatorjson_pointer.cpp -o operatorjson_pointer 
Since
version 2.0.0

Definition at line 19559 of file json.hpp.