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 = int64_t, class NumberFloatType = double, template< typename U > class AllocatorType = std::allocator>
Returns a const reference to the element at specified location idx, with bounds checking.
- Parameters
-
[in] | idx | index of the element to access |
- Returns
- const 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 using at.
8 json array = {
"first",
"2nd",
"third",
"fourth"};
11 std::cout << array.
at(2) <<
'\n';
16 std::cout << array.
at(5) <<
'\n';
18 catch (std::out_of_range)
20 std::cout <<
"out of range" <<
'\n';
a class to store JSON values
reference at(size_type idx)
access specified array element with bounds checking
namespace for Niels Lohmann
Output (play with this example online): "third"
out of range
The example code above can be translated withg++ -std=c++11 -Isrc doc/examples/at__size_type_const.cpp -o at__size_type_const
- Since
- version 1.0.0
Definition at line 2773 of file json.hpp.