JSON for Modern C++ 2.1.1

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
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
exception
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
insert
invalid_iterator
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=
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operator==
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operator>
operator>
operator>
operator>=
operator>=
operator>=
operator>>
operator>>
operator[]
operator[]
operator[]
operator[]
operator[]
operator[]
operator[]
operator[]
operator[]
operator[]
other_error
out_of_range
parse
parse
parse
parse
parse
parse
parse_error
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_error
type_name
unflatten
value
value
value
value
value_t
value_type
~basic_json
| ## ◆ at() [4/6] 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>
const_reference nlohmann::basic_json::at | ( | const typename object_t::key_type & | key | ) | const
| inline
  Returns a const reference to the element at with specified key key, with bounds checking. Parameters
  [in] | key | key of the element to access
  Returns const reference to the element at key key Exceptions
  type_error.304 | if the JSON value is not an object; in this case, calling `at` with a key makes no sense. See example below.
  out_of_range.403 | if the key key is is not stored in the object; that is, `find(key) == end()`. See example below.
  Exception safety Strong guarantee: if an exception is thrown, there are no changes in the JSON value. Complexity Logarithmic in the size of the container. See also operator[](const typename object_t::key_type&) for unchecked access by reference value() for access by value with a default value Since version 1.0.0 Example The example below shows how object elements can be read using `at()`. It also demonstrates the different exceptions that can be thrown. 1 #include "json.hpp" 2 3 using json = nlohmann::json; 4 5 int main() 6 { 7 // create JSON object 8 json object = 9 { 10 {"the good", "il buono"}, 11 {"the bad", "il cattivo"}, 12 {"the ugly", "il brutto"} 13 }; 14 15 // output element with key "the ugly" 16 std::cout << object.at("the ugly") << '\n'; 17 18 19 // exception type_error.304 20 try 21 { 22 // use at() on a non-object type 23 const json str = "I am a string"; 24 std::cout << str.at("the good") << '\n'; 25 } 26 catch (json::type_error& e) 27 { 28 std::cout << e.what() << '\n'; 29 } 30 31 // exception out_of_range.401 32 try 33 { 34 // try to read from a nonexisting key 35 std::cout << object.at("the fast") << '\n'; 36 } 37 catch (json::out_of_range) 38 { 39 std::cout << "out of range" << '\n'; 40 } 41 } nlohmann::json basic_json<> json default JSON class Definition: json.hpp:13933 nlohmann::basic_json::out_of_range detail::out_of_range out_of_range exception indicating access out of the defined range Definition: json.hpp:1324 nlohmann::basic_json::type_error detail::type_error type_error exception indicating executing a member function with a wrong type Definition: json.hpp:1322 Output (play with this example online):
      "il brutto"
      [json.exception.type_error.304] cannot use at() with string
      out of range
  The example code above can be translated with
      g++ -std=c++11 -Isrc doc/examples/
      at__object_t_key_type_const.cpp -o
      at__object_t_key_type_const
Definition at line 3937 of file json.hpp.