at() [6/6]

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, class BinaryType = std::vector<std::uint8_t>>

const_reference nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType >::at ( size_type  idx ) const

inline

access specified array element with bounds checking

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

type_error.304	if the JSON value is not an array; in this case, calling at with an index makes no sense. See example below.
out_of_range.401	if the index idx is out of range of the array; that is, idx >= size(). See example below.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@complexity Constant.

Since

version 1.0.0

@liveexample{The example below shows how array elements can be read using at(). It also demonstrates the different exceptions that can be thrown., at__size_type_const}

Definition at line 21234 of file json.hpp.

    {
        // at only works for arrays
        if (JSON_HEDLEY_LIKELY(is_array()))
        {
            JSON_TRY
            {
                return m_value.array->at(idx);
            }
            JSON_CATCH (std::out_of_range &)
            {
                // create better exception explanation
                JSON_THROW(out_of_range::create(401, "array index " + std::to_string(idx) + " is out of range", *this));
            }
        }
 
        else
        {
            JSON_THROW(type_error::create(304, "cannot use at() with " + std::string(type_name()), *this));
        }
    }