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+=
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operator<
operator<
operator<
operator<<
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operator<=
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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
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to_cbor
to_msgpack
type
type_error
type_name
unflatten
value
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value_t
value_type
~basic_json
| ## ◆ at() [2/6] 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 | ( | size_type | idx | ) | const
| inline
  Returns a const reference to the element at specified location idx, with bounds checking. Parameters
  [in] | idx | index of the element to access
  Returns const reference to the element at index idx Exceptions
  type_error.304 | if the JSON value is not an array; in this case, calling `at` with an index makes no sense. See example below.
  out_of_range.401 | if the index idx is out of range of the array; that is, `idx >= size()`. See example below.
  Exception safety Strong guarantee: if an exception is thrown, there are no changes in the JSON value. Complexity Constant. Since version 1.0.0 Example The example below shows how array 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 array 8 const json array = {"first", "2nd", "third", "fourth"}; 9 10 // output element at index 2 (third element) 11 std::cout << array.at(2) << '\n'; 12 13 14 // exception type_error.304 15 try 16 { 17 // use at() on a non-array type 18 const json str = "I am a string"; 19 std::cout << str.at(0) << '\n'; 20 } 21 catch (json::type_error& e) 22 { 23 std::cout << e.what() << '\n'; 24 } 25 26 // exception out_of_range.401 27 try 28 { 29 // try to read beyond the array limit 30 std::cout << array.at(5) << '\n'; 31 } 32 catch (json::out_of_range& e) 33 { 34 std::cout << e.what() << '\n'; 35 } 36 } 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):
      "third"
      [json.exception.type_error.304] cannot use at() with string
      [json.exception.out_of_range.401] 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_const.cpp -o
      at__size_type_const
Definition at line 3831 of file json.hpp.