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api/basic_json/empty/index.md

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+# nlohmann::basic_json::empty
+
+```
+bool empty() const noexcept;
+```
+
+Checks if a JSON value has no elements (i.e., whether its [`size()`](https://json.nlohmann.me/api/basic_json/size/index.md) is `0`).
+
+## Return value
+
+The return value depends on the different types and is defined as follows:
+
+| Value type | return value                           |
+| ---------- | -------------------------------------- |
+| null       | `true`                                 |
+| boolean    | `false`                                |
+| string     | `false`                                |
+| number     | `false`                                |
+| binary     | `false`                                |
+| object     | result of function `object_t::empty()` |
+| array      | result of function `array_t::empty()`  |
+
+## 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 `empty()` functions have constant complexity.
+
+## Possible implementation
+
+```
+bool empty() const noexcept
+{
+    return size() == 0;
+}
+```
+
+## Notes
+
+This function does not return whether a string stored as JSON value is empty -- it returns whether the JSON container itself is empty which is `false` in the case of a string.
+
+## Examples
+
+Example
+
+The following code uses `empty()` to check if a JSON object contains any elements.
+
+```
+#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 empty()
+    std::cout << std::boolalpha;
+    std::cout << j_null.empty() << '\n';
+    std::cout << j_boolean.empty() << '\n';
+    std::cout << j_number_integer.empty() << '\n';
+    std::cout << j_number_float.empty() << '\n';
+    std::cout << j_object.empty() << '\n';
+    std::cout << j_object_empty.empty() << '\n';
+    std::cout << j_array.empty() << '\n';
+    std::cout << j_array_empty.empty() << '\n';
+    std::cout << j_string.empty() << '\n';
+}
+```
+
+Output:
+
+```
+true
+false
+false
+false
+false
+true
+false
+true
+false
+```
+
+## Version history
+
+- Added in version 1.0.0.
+- Extended to return `false` for binary types in version 3.8.0.