JSON for Modern C++ 2.1.1
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◆ max_size()

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>
size_type nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::max_size ( ) const
inlinenoexcept

Returns the maximum number of elements a JSON value is able to hold due to system or library implementation limitations, i.e. std::distance(begin(), end()) for the JSON value.

Returns
The return value depends on the different types and is defined as follows:
Value type return value
null 0 (same as size())
boolean 1 (same as size())
string 1 (same as size())
number 1 (same as size())
object result of function object_t::max_size()
array result of function array_t::max_size()
Complexity\n Constant, as long as @ref array_t and @ref object_t satisfy
the Container concept; that is, their max_size() functions have constant complexity.
Requirements\n This function helps basic_json satisfying the
Container requirements:
  • The complexity is constant.
  • Has the semantics of returning b.size() where b is the largest possible JSON value.
Example\n The following code calls max_size() on the different value
types. Note the output is implementation specific.
1#include <json.hpp>
2
3using json = nlohmann::json;
4
5int main()
6{
7 // create JSON values
9 json j_boolean = true;
11 json j_number_float = 23.42;
12 json j_object = {{"one", 1}, {"two", 2}};
13 json j_array = {1, 2, 4, 8, 16};
14 json j_string = "Hello, world";
15
16 // call max_size()
17 std::cout << j_null.max_size() << '\n';
18 std::cout << j_boolean.max_size() << '\n';
19 std::cout << j_number_integer.max_size() << '\n';
20 std::cout << j_number_float.max_size() << '\n';
21 std::cout << j_object.max_size() << '\n';
22 std::cout << j_array.max_size() << '\n';
23 std::cout << j_string.max_size() << '\n';
24}
size_type max_size() const noexcept
returns the maximum possible number of elements
Definition json.hpp:5129
static basic_json array(std::initializer_list< basic_json > init=std::initializer_list< basic_json >())
explicitly create an array from an initializer list
Definition json.hpp:2165
a class to store JSON values
Definition json.hpp:1040
basic_json<> json
default JSON class
Definition json.hpp:12369

Output (play with this example online):
0
1
1
1
256204778801521550
1152921504606846975
1

The example code above can be translated with
g++ -std=c++11 -Isrc doc/examples/max_size.cpp -o max_size 
See also
size() – returns the number of elements
Since
version 1.0.0

Definition at line 5129 of file json.hpp.