mirror of
https://github.com/nlohmann/json.git
synced 2026-07-29 07:03:02 +04:00
nlohmann
91 lines
2.3 KiB
Markdown
91 lines
2.3 KiB
Markdown
# nlohmann::basic_json::size
|
|
|
|
```
|
|
size_type size() const noexcept;
|
|
```
|
|
|
|
Returns the number of elements in a JSON value.
|
|
|
|
## Return value
|
|
|
|
The return value depends on the different types and is defined as follows:
|
|
|
|
| Value type | return value |
|
|
| ---------- | ----------------------------------- |
|
|
| null | `0` |
|
|
| boolean | `1` |
|
|
| string | `1` |
|
|
| number | `1` |
|
|
| binary | `1` |
|
|
| object | result of function object_t::size() |
|
|
| array | result of function array_t::size() |
|
|
|
|
## Exception safety
|
|
|
|
No-throw guarantee: this function never throws exceptions.
|
|
|
|
## Complexity
|
|
|
|
Constant, as long as [`array_t`](https://json.nlohmann.me/api/basic_json/array_t/index.md) and [`object_t`](https://json.nlohmann.me/api/basic_json/object_t/index.md) satisfy the [Container](https://en.cppreference.com/w/cpp/named_req/Container) concept; that is, their `size()` functions have constant complexity.
|
|
|
|
## Notes
|
|
|
|
This function does not return the length of a string stored as JSON value -- it returns the number of elements in the JSON value which is `1` in the case of a string.
|
|
|
|
## Examples
|
|
|
|
Example
|
|
|
|
The following code calls `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_object_empty(json::value_t::object);
|
|
json j_array = {1, 2, 4, 8, 16};
|
|
json j_array_empty(json::value_t::array);
|
|
json j_string = "Hello, world";
|
|
|
|
// call size()
|
|
std::cout << j_null.size() << '\n';
|
|
std::cout << j_boolean.size() << '\n';
|
|
std::cout << j_number_integer.size() << '\n';
|
|
std::cout << j_number_float.size() << '\n';
|
|
std::cout << j_object.size() << '\n';
|
|
std::cout << j_object_empty.size() << '\n';
|
|
std::cout << j_array.size() << '\n';
|
|
std::cout << j_array_empty.size() << '\n';
|
|
std::cout << j_string.size() << '\n';
|
|
}
|
|
```
|
|
|
|
Output:
|
|
|
|
```
|
|
0
|
|
1
|
|
1
|
|
1
|
|
2
|
|
0
|
|
5
|
|
0
|
|
1
|
|
```
|
|
|
|
## Version history
|
|
|
|
- Added in version 1.0.0.
|
|
- Extended to return `1` for binary types in version 3.8.0.
|