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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.

Example

Example

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

#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
256204778801521550
1152921504606846975
1

Version history

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