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◆ 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>
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
-
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\n Logarithmic in the size of the container.
- Example\n The example below shows how object elements can be read using
at() .
10 { "the good", "il buono"},
11 { "the bad", "il cattivo"},
12 { "the ugly", "il brutto"}
16 std::cout << object. at( "the ugly") << '\n';
21 std::cout << object. at( "the fast") << '\n';
23 catch (std::out_of_range)
25 std::cout << "out of range" << '\n';
static basic_json array(std::initializer_list< basic_json > init=std::initializer_list< basic_json >()) explicitly create an array from an initializer list
reference at(size_type idx) access specified array element with bounds checking
a class to store JSON values
basic_json<> json default JSON class
Output (play with this example online):
"il brutto"
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
- 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 3668 of file json.hpp.
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