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>
Returns a reference to the element at with specified key key, with bounds checking.
- Parameters
-
[in] | key | key of the element to access |
- Returns
- reference to the element at key key
- Exceptions
-
std::domain_error | if the JSON value is not an object; example: "cannot use at() with boolean" |
std::out_of_range | if the key key is is not stored in the object; that is, find(key) == end() ; example: "key "the fast" not found" |
- Complexity
- Logarithmic in the size of the container.
- Example
- The example below shows how object elements can be read and written using
at()
. 10 {
"the good",
"il buono"},
11 {
"the bad",
"il cativo"},
12 {
"the ugly",
"il brutto"}
16 std::cout <<
object.at(
"the ugly") <<
'\n';
19 object.at(
"the bad") =
"il cattivo";
22 std::cout <<
object <<
'\n';
27 object.at(
"the fast") =
"il rapido";
29 catch (std::out_of_range& e)
31 std::cout <<
"out of range: " << e.what() <<
'\n';
basic_json<> json
default JSON class
Output (play with this example online): "il brutto"
{"the bad":"il cattivo","the good":"il buono","the ugly":"il brutto"}
out of range: key 'the fast' not found
The example code above can be translated withg++ -std=c++11 -Isrc doc/examples/at__object_t_key_type.cpp -o at__object_t_key_type
- 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
Definition at line 3131 of file json.hpp.