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 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
-
std::domain_error | if the JSON value is not an array; example: "cannot use at() with string" |
std::out_of_range | if the index idx is out of range of the array; that is, idx >= size() ; example: "array index 7 is out of range" |
- Complexity
- Constant.
- Example
- The example below shows how array elements can be read and written using
at()
. 8 json array = {
"first",
"2nd",
"third",
"fourth"};
11 std::cout << array.
at(2) <<
'\n';
14 array.
at(1) =
"second";
17 std::cout << array <<
'\n';
22 array.
at(5) =
"sixth";
24 catch (std::out_of_range& e)
26 std::cout <<
"out of range: " << e.what() <<
'\n';
basic_json<> json
default JSON class
reference at(size_type idx)
access specified array element with bounds checking
static basic_json array(std::initializer_list< basic_json > init=std::initializer_list< basic_json >())
explicitly create an array from an initializer list
Output (play with this example online): "third"
["first","second","third","fourth"]
out of range: array index 5 is out of range
The example code above can be translated withg++ -std=c++11 -Isrc doc/examples/at__size_type.cpp -o at__size_type
- Since
- version 1.0.0
Definition at line 3531 of file json.hpp.