empty - JSON for Modern C++ (original) (raw)

nlohmann::basic_json::empty

bool empty() const noexcept;

Checks if a JSON value has no elements (i.e., whether its size() 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 and object_t satisfy the 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 #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

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