JSON for Modern C++  2.0.3
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>
reference nlohmann::basic_json::at ( size_type  idx)
inline

Returns a reference to the element at specified location idx, with bounds checking.

Parameters
[in]idxindex of the element to access
Returns
reference to the element at index idx
Exceptions
std::domain_errorif the JSON value is not an array; example: "cannot use at() with string"
std::out_of_rangeif 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().
1 #include <json.hpp>
2 
3 using json = nlohmann::json;
4 
5 int main()
6 {
7  // create JSON array
8  json array = {"first", "2nd", "third", "fourth"};
9 
10  // output element at index 2 (third element)
11  std::cout << array.at(2) << '\n';
12 
13  // change element at index 1 (second element) to "second"
14  array.at(1) = "second";
15 
16  // output changed array
17  std::cout << array << '\n';
18 
19  // try to write beyond the array limit
20  try
21  {
22  array.at(5) = "sixth";
23  }
24  catch (std::out_of_range& e)
25  {
26  std::cout << "out of range: " << e.what() << '\n';
27  }
28 }
basic_json<> json
default JSON class
Definition: json.hpp:10122
static basic_json array(std::initializer_list< basic_json > init=std::initializer_list< basic_json >())
explicitly create an array from an initializer list
Definition: json.hpp:1716
reference at(size_type idx)
access specified array element with bounds checking
Definition: json.hpp:3147
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 with
g++ -std=c++11 -Isrc doc/examples/at__size_type.cpp -o at__size_type 
Since
version 1.0.0

Definition at line 3147 of file json.hpp.