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

at() [1/6] 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> reference nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::at ( size_type  idx ) inline Returns a reference to the element at specified location idx, with bounds checking. Parameters [in] idx index of the element to access Returns reference to the element at index idx Exceptions std::domain_error if the JSON value is not an array; example: "cannot use at() with string" std::out_of_range if the index idx is out of range of the array; that is, idx >= size(); example: "array index 7 is out of range" Complexity Constant. Example The example below shows how array elements can be read and written using at(). #include <json.hpp> using json = nlohmann::json; int main() { // create JSON array json array = {"first", "2nd", "third", "fourth"}; // output element at index 2 (third element) std::cout << array.at(2) << '\n'; // change element at index 1 (second element) to "second" array.at(1) = "second"; // output changed array std::cout << array << '\n'; // try to write beyond the array limit try { array.at(5) = "sixth"; } catch (std::out_of_range& e) { std::cout << "out of range: " << e.what() << '\n'; } } Output (play with this example online): "third" ["first","second","third","fourth"] out of range: array index 5 is out of range The example code above can be translated with g++ -std=c++11 -Isrc doc/examples/at__size_type.cpp -o at__size_type Since version 1.0.0 Definition at line 3540 of file json.hpp.