nlohmann::basic_json::max_size¶

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.

Return 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()`

Exception safety¶

No-throw guarantee: this function never throws exceptions.

Complexity¶

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

Notes¶

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.

Examples¶

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.

Version history¶

Added in version 1.0.0.
Extended to return 1 for binary types in version 3.8.0.