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 = int64_t, class NumberFloatType = double, template< typename U > class AllocatorType = std::allocator>

size_type nlohmann::basic_json::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 value types and is defined as follows:

Value type	return value
null	0
boolean	1
string	1
number	1
object	result of function object_t::max_size()
array	result of function array_t::max_size()

Complexity

Constant, as long as array_t and object_t satisfy the Container concept; that is, their max_size() functions have constant complexity.

Requirements

This function satisfies the Container requirements:

• The complexity is constant.
• Has the semantics of returning b.size() where b is the largest possible JSON value.

Example

The following code calls max_size on the different value types. Note the output is implementation specific.

#include <json.hpp>

using namespace nlohmann;

int main()
{
    // create JSON values
    json j_null;
    json j_boolean = true;
    json j_number_integer = 17;
    json j_number_float = 23.42;
    json j_object = {{"one", 1}, {"two", 2}};
    json j_array = {1, 2, 4, 8, 16};
    json j_string = "Hello, world";

    // call max_size()
    std::cout << j_null.max_size() << '\n';
    std::cout << j_boolean.max_size() << '\n';
    std::cout << j_number_integer.max_size() << '\n';
    std::cout << j_number_float.max_size() << '\n';
    std::cout << j_object.max_size() << '\n';
    std::cout << j_array.max_size() << '\n';
    std::cout << j_string.max_size() << '\n';
}

Output:

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 

.