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api/basic_json/size/index.md

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+# 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.