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99 lines
2.7 KiB
Markdown
99 lines
2.7 KiB
Markdown
# <small>nlohmann::basic_json::</small>max_size
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```cpp
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size_type max_size() const noexcept;
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```
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Returns the maximum number of elements a JSON value is able to hold due to system or library implementation limitations,
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i.e. `std::distance(begin(), end())` for the JSON value.
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## Return value
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The return value depends on the different types and is defined as follows:
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| Value type | return value |
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|------------|-------------------------------------------|
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| null | `0` (same as [`size()`](size.md)) |
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| boolean | `1` (same as [`size()`](size.md)) |
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| string | `1` (same as [`size()`](size.md)) |
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| number | `1` (same as [`size()`](size.md)) |
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| binary | `1` (same as [`size()`](size.md)) |
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| object | result of function `object_t::max_size()` |
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| array | result of function `array_t::max_size()` |
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## Exception safety
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No-throw guarantee: this function never throws exceptions.
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## Complexity
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Constant, as long as [`array_t`](array_t.md) and [`object_t`](object_t.md) satisfy the
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[Container](https://en.cppreference.com/w/cpp/named_req/Container) concept; that is, their `max_size()` functions have
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constant complexity.
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## Notes
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This function does not return the maximal length of a string stored as JSON value -- it returns the maximal number of
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string elements the JSON value can store which is `1`.
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## Examples
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??? example
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The following code calls `max_size()` on the different value types.
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```cpp
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#include <iostream>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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int main()
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{
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// create JSON values
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json j_null;
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json j_boolean = true;
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json j_number_integer = 17;
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json j_number_float = 23.42;
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json j_object = {{"one", 1}, {"two", 2}};
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json j_array = {1, 2, 4, 8, 16};
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json j_string = "Hello, world";
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// call max_size()
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std::cout << j_null.max_size() << '\n';
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std::cout << j_boolean.max_size() << '\n';
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std::cout << j_number_integer.max_size() << '\n';
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std::cout << j_number_float.max_size() << '\n';
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std::cout << j_object.max_size() << '\n';
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std::cout << j_array.max_size() << '\n';
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std::cout << j_string.max_size() << '\n';
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}
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```
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Output:
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```json
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0
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1
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1
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1
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115292150460684697
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576460752303423487
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1
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```
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Note the output is platform-dependent.
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## See also
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- [size](size.md) returns the number of elements
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- [array_t](array_t.md) the type used to store JSON arrays
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- [object_t](object_t.md) the type used to store JSON objects
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## Version history
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- Added in version 1.0.0.
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- Extended to return `1` for binary types in version 3.8.0.
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