JSON for Modern C++ 3.7.1

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
begin
begin
boolean_t
cbegin
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_cbor
from_cbor
from_msgpack
from_msgpack
from_ubjson
from_ubjson
front
front
get
get
get
get
get
get
get_allocator
get_ptr
get_ptr
get_ref
get_ref
get_to
get_to
initializer_list_t
input_format_t
insert
insert
insert
insert
insert
insert
insert_iterator
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
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_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
size
size_type
string_t
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
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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 | ( | const json_pointer & | ptr | ) | const
| inline
  Returns a const reference to the element at with specified JSON pointer ptr, with bounds checking. Parameters
  [in] | ptr | JSON pointer to the desired element
  Returns reference to the element pointed to by ptr Exceptions
  parse_error.106 | if an array index in the passed JSON pointer ptr begins with '0'. See example below.
  parse_error.109 | if an array index in the passed JSON pointer ptr is not a number. See example below.
  out_of_range.401 | if an array index in the passed JSON pointer ptr is out of range. See example below.
  out_of_range.402 | if the array index '-' is used in the passed JSON pointer ptr. As `at` provides checked access (and no elements are implicitly inserted), the index '-' is always invalid. See example below.
  out_of_range.403 | if the JSON pointer describes a key of an object which cannot be found. See example below.
  out_of_range.404 | if the JSON pointer ptr can not be resolved. See example below.
  Exception safety Strong guarantee: if an exception is thrown, there are no changes in the JSON value. Complexity Constant. Since version 2.0.0 Example The behavior is shown in the example. 1 #include <iostream> 2 #include <nlohmann/json.hpp> 3 4 using json = nlohmann::json; 5 6 int main() 7 { 8 // create a JSON value 9 const json j = 10 { 11 {"number", 1}, {"string", "foo"}, {"array", {1, 2}} 12 }; 13 14 // read-only access 15 16 // output element with JSON pointer "/number" 17 std::cout << j.at("/number"_json_pointer) << '\n'; 18 // output element with JSON pointer "/string" 19 std::cout << j.at("/string"_json_pointer) << '\n'; 20 // output element with JSON pointer "/array" 21 std::cout << j.at("/array"_json_pointer) << '\n'; 22 // output element with JSON pointer "/array/1" 23 std::cout << j.at("/array/1"_json_pointer) << '\n'; 24 25 // out_of_range.109 26 try 27 { 28 // try to use an array index that is not a number 29 json::const_reference ref = j.at("/array/one"_json_pointer); 30 } 31 catch (json::parse_error& e) 32 { 33 std::cout << e.what() << '\n'; 34 } 35 36 // out_of_range.401 37 try 38 { 39 // try to use a an invalid array index 40 json::const_reference ref = j.at("/array/4"_json_pointer); 41 } 42 catch (json::out_of_range& e) 43 { 44 std::cout << e.what() << '\n'; 45 } 46 47 // out_of_range.402 48 try 49 { 50 // try to use the array index '-' 51 json::const_reference ref = j.at("/array/-"_json_pointer); 52 } 53 catch (json::out_of_range& e) 54 { 55 std::cout << e.what() << '\n'; 56 } 57 58 // out_of_range.403 59 try 60 { 61 // try to use a JSON pointer to an nonexistent object key 62 json::const_reference ref = j.at("/foo"_json_pointer); 63 } 64 catch (json::out_of_range& e) 65 { 66 std::cout << e.what() << '\n'; 67 } 68 69 // out_of_range.404 70 try 71 { 72 // try to use a JSON pointer that cannot be resolved 73 json::const_reference ref = j.at("/number/foo"_json_pointer); 74 } 75 catch (json::out_of_range& e) 76 { 77 std::cout << e.what() << '\n'; 78 } 79 } Output (play with this example online):
      1
      "foo"
      [1,2]
      2
      [json.exception.parse_error.109] parse error: array index 'one' is not a number
      [json.exception.out_of_range.401] array index 4 is out of range
      [json.exception.out_of_range.402] array index '-' (2) is out of range
      [json.exception.out_of_range.403] key 'foo' not found
      [json.exception.out_of_range.404] unresolved reference token 'foo'
  The example code above can be translated with
      g++ -std=c++11 -Isingle_include doc/examples/at_json_pointer_const.cpp -o at_json_pointer_const
Definition at line 21948 of file json.hpp.

nlohmann::basic_json::const_reference
const value_type & const_reference
the type of an element const reference
Definition: json.hpp:14804
nlohmann::basic_json::at
reference at(size_type idx)
access specified array element with bounds checking
Definition: json.hpp:17472
nlohmann::basic_json::parse_error
detail::parse_error parse_error
exception indicating a parse error
Definition: json.hpp:14776
nlohmann::basic_json::out_of_range
detail::out_of_range out_of_range
exception indicating access out of the defined range
Definition: json.hpp:14782
nlohmann::json
basic_json<> json
default JSON class
Definition: json.hpp:2445