size_type max_size() const noexcept;
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.
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()) |
| binary | 1 (same as size()) |
| object | result of function object_t::max_size() |
| array | result of function array_t::max_size() |
No-throw guarantee: this function never throws exceptions.
Constant, as long as array_t and object_t satisfy the Container concept; that is, their max_size() functions have constant complexity.
This function does not return the maximal length of a string stored as JSON value -- it returns the maximal number of string elements the JSON value can store which is 1.
Example
The following code calls max_size() on the different value types.
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
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 115292150460684697 576460752303423487 1
Note the output is platform-dependent.
1 for binary types in version 3.8.0.