JSON for Modern C++  3.7.2

◆ 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::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()
Example
The following code calls max_size() on the different value types. Note the output is implementation specific.
1 #include <iostream>
2 #include <nlohmann/json.hpp>
3 
4 using json = nlohmann::json;
5 
6 int main()
7 {
8  // create JSON values
9  json j_null;
10  json j_boolean = true;
11  json j_number_integer = 17;
12  json j_number_float = 23.42;
13  json j_object = {{"one", 1}, {"two", 2}};
14  json j_array = {1, 2, 4, 8, 16};
15  json j_string = "Hello, world";
16 
17  // call max_size()
18  std::cout << j_null.max_size() << '\n';
19  std::cout << j_boolean.max_size() << '\n';
20  std::cout << j_number_integer.max_size() << '\n';
21  std::cout << j_number_float.max_size() << '\n';
22  std::cout << j_object.max_size() << '\n';
23  std::cout << j_array.max_size() << '\n';
24  std::cout << j_string.max_size() << '\n';
25 }

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 -Isingle_include doc/examples/max_size.cpp -o 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.
Iterator validity
No changes.
Exception safety
No-throw guarantee: this function never throws exceptions.
Requirements
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.
See also
size() – returns the number of elements
Since
version 1.0.0

Definition at line 19277 of file json.hpp.

nlohmann::json
basic_json<> json
default JSON class
Definition: json.hpp:2445