JSON for Modern C++ 3.8.0

accept
accept
accept
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
basic_json
begin
begin
binary
binary
binary
binary
binary_t
boolean_t
cbegin
cbor_tag_handler_t
cend
clear
const_iterator
const_pointer
const_reference
const_reverse_iterator
contains
contains
count
crbegin
crend
detail::external_constructor
diff
difference_type
dump
emplace
emplace_back
empty
end
end
erase
erase
erase
erase
error_handler_t
exception
find
find
flatten
from_bson
from_bson
from_bson
from_bson
from_cbor
from_cbor
from_cbor
from_cbor
from_msgpack
from_msgpack
from_msgpack
from_msgpack
from_ubjson
from_ubjson
from_ubjson
from_ubjson
front
front
get
get
get
get
get
get
get_allocator
get_binary
get_binary
get_ptr
get_ptr
get_ref
get_ref
get_to
get_to
get_to
initializer_list_t
input_format_t
insert
insert
insert
insert
insert
insert
insert_iterator
invalid_iterator
is_array
is_binary
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
items
items
iterator
iterator_wrapper
iterator_wrapper
json_pointer
json_sax_t
json_serializer
max_size
merge_patch
meta
number_float_t
number_integer_t
number_unsigned_t
object
object_comparator_t
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[]
operator[]
operator[]
operator[]
operator[]
operator[]
operator[]
other_error
out_of_range
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
sax_parse
sax_parse
sax_parse
size
size_type
string_t
swap
swap
swap
swap
swap
swap
swap
to_bson
to_bson
to_bson
to_cbor
to_cbor
to_cbor
to_msgpack
to_msgpack
to_msgpack
to_ubjson
to_ubjson
to_ubjson
type
type_error
type_name
unflatten
update
update
value
value
value
value
value_t
value_type
~basic_json
| ## ◆ at() [5/6]
reference nlohmann::basic_json::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
  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 and written using `at()`. It also demonstrates the different exceptions that can be thrown. 1 #include <iostream> 2 #include <nlohmann/json.hpp> 3 4 using json = nlohmann::json; 5 6 int main() 7 { 8 // create JSON array 9 json array = {"first", "2nd", "third", "fourth"}; 10 11 // output element at index 2 (third element) 12 std::cout << array.at(2) << '\n'; 13 14 // change element at index 1 (second element) to "second" 15 array.at(1) = "second"; 16 17 // output changed array 18 std::cout << array << '\n'; 19 20 21 // exception type_error.304 22 try 23 { 24 // use at() on a non-array type 25 json str = "I am a string"; 26 str.at(0) = "Another string"; 27 } 28 catch (json::type_error& e) 29 { 30 std::cout << e.what() << '\n'; 31 } 32 33 // exception out_of_range.401 34 try 35 { 36 // try to write beyond the array limit 37 array.at(5) = "sixth"; 38 } 39 catch (json::out_of_range& e) 40 { 41 std::cout << e.what() << '\n'; 42 } 43 } Output (play with this example online):
      "third"
      ["first","second","third","fourth"]
      [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 -Isingle_include doc/examples/at__size_type.cpp -o at__size_type
Definition at line 19693 of file json.hpp.

nlohmann::basic_json::at
reference at(size_type idx)
access specified array element with bounds checking
Definition: json.hpp:19693
nlohmann::basic_json::type_error
detail::type_error type_error
exception indicating executing a member function with a wrong type
Definition: json.hpp:16645
nlohmann::basic_json::array
static basic_json array(initializer_list_t init={})
explicitly create an array from an initializer list
Definition: json.hpp:18170
nlohmann::basic_json::out_of_range
detail::out_of_range out_of_range
exception indicating access out of the defined range
Definition: json.hpp:16647
nlohmann::json
basic_json<> json
default JSON class
Definition: json.hpp:2933