JSON for Modern C++  2.0.6

§ get() [3/3]

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 PointerType , typename std::enable_if< std::is_pointer< PointerType >::value, int >::type = 0>
constexpr const PointerType nlohmann::basic_json::get ( ) const
inlinenoexcept

get a pointer value (explicit) Explicit pointer access to the internally stored JSON value. No copies are made.

Warning
The pointer becomes invalid if the underlying JSON object changes.
Template Parameters
PointerTypepointer type; must be a pointer to array_t, object_t, string_t, boolean_t, number_integer_t, number_unsigned_t, or number_float_t.
Returns
pointer to the internally stored JSON value if the requested pointer type PointerType fits to the JSON value; nullptr otherwise
Complexity
Constant.
Example
The example below shows how pointers to internal values of a JSON value can be requested. Note that no type conversions are made and a nullptr is returned if the value and the requested pointer type does not match.
1 #include <json.hpp>
2 
3 using json = nlohmann::json;
4 
5 int main()
6 {
7  // create a JSON number
8  json value = 17;
9 
10  // explicitly getting pointers
11  auto p1 = value.get<const json::number_integer_t*>();
12  auto p2 = value.get<json::number_integer_t*>();
13  auto p3 = value.get<json::number_integer_t* const>();
14  auto p4 = value.get<const json::number_integer_t* const>();
15  auto p5 = value.get<json::number_float_t*>();
16 
17  // print the pointees
18  std::cout << *p1 << ' ' << *p2 << ' ' << *p3 << ' ' << *p4 << '\n';
19  std::cout << std::boolalpha << (p5 == nullptr) << '\n';
20 }
basic_json<> json
default JSON class
Definition: json.hpp:10155
NumberIntegerType number_integer_t
a type for a number (integer)
Definition: json.hpp:586
ValueType value(const typename object_t::key_type &key, ValueType default_value) const
access specified object element with default value
Definition: json.hpp:3699
NumberFloatType number_float_t
a type for a number (floating-point)
Definition: json.hpp:725
Output (play with this example online):
17 17 17 17
true
The example code above can be translated with
g++ -std=c++11 -Isrc doc/examples/get__PointerType.cpp -o get__PointerType 
See also
get_ptr() for explicit pointer-member access
Since
version 1.0.0

Definition at line 2947 of file json.hpp.