allocator_type array array_t at at at at at at back back basic_json basic_json basic_json basic_json basic_json basic_json basic_json basic_json basic_json begin begin boolean_t cbegin cend clear const_iterator const_pointer const_reference const_reverse_iterator count crbegin crend detail::external_constructor diff difference_type dump emplace emplace_back empty end end erase erase erase erase find find flatten from_cbor from_msgpack front front get get get get get get_allocator get_ptr get_ptr get_ref get_ref insert insert insert insert insert is_array is_boolean is_discarded is_null is_number is_number_float is_number_integer is_number_unsigned is_object is_primitive is_string is_structured iterator iterator_wrapper iterator_wrapper json_serializer max_size meta number_float_t number_integer_t number_unsigned_t object object_t operator value_t operator ValueType operator!= operator!= operator!= operator+= operator+= operator+= operator+= operator< operator<< operator<< operator<= operator= operator== operator== operator== operator> operator>= operator>> operator>> operator[] operator[] operator[] operator[] operator[] operator[] operator[] operator[] operator[] operator[] parse parse parse parse parse parse parse_event_t parser_callback_t patch pointer push_back push_back push_back push_back rbegin rbegin reference rend rend reverse_iterator size size_type string_t swap swap swap swap to_cbor to_msgpack type type_name unflatten value value value value value_t value_type ~basic_json

empty() template<template< typename U, typename V, typename... Args > class ObjectType = std::map, template< typename U, typename... Args > class ArrayType = std::vector, class StringType = std::string, class BooleanType = bool, class NumberIntegerType = std::int64_t, class NumberUnsignedType = std::uint64_t, class NumberFloatType = double, template< typename U > class AllocatorType = std::allocator, template< typename T, typename SFINAE=void > class JSONSerializer = adl_serializer> bool nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::empty ( ) const inlinenoexcept Checks if a JSON value has no elements. Returns 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 object result of function object_t::empty() array result of function array_t::empty() Note 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. Complexity Constant, as long as array_t and object_t satisfy the Container concept; that is, their empty() functions have constant complexity. Requirements This function helps basic_json satisfying the Container requirements: The complexity is constant. Has the semantics of begin() == end(). Example The following code uses empty() to check if a JSON object contains any elements. #include <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 (play with this example online): true false false false false true false true false The example code above can be translated with g++ -std=c++11 -Isrc doc/examples/empty.cpp -o empty See also size() – returns the number of elements Since version 1.0.0 Definition at line 5004 of file json.hpp.