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◆ operator[]() [5/8]
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>>
reference nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType >::operator[] |
( |
size_type |
idx | ) |
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inline |
Returns a reference to the element at specified location idx.
- Note
- If idx is beyond the range of the array (i.e.,
idx >= size() ), then the array is silently filled up with null values to make idx a valid reference to the last stored element.
- Parameters
-
[in] | idx | index of the element to access |
- Returns
- reference to the element at index idx
- Exceptions
-
type_error.305 | if the JSON value is not an array or null; in that cases, using the [] operator with an index makes no sense. |
- Complexity
- Constant if idx is in the range of the array. Otherwise linear in
idx - size() .
- Example
- The example below shows how array elements can be read and written using
[] operator. Note the addition of null values.
2 #include <nlohmann/json.hpp>
9 json array = {1, 2, 3, 4, 5};
12 std::cout << array[3] << '\n';
15 array[array.size() - 1] = 6;
18 std::cout << array << '\n';
24 std::cout << array << '\n';
basic_json<> json default JSON class
Output (play with this example online): 4
[1,2,3,4,6]
[1,2,3,4,6,null,null,null,null,null,11]
The example code above can be translated withg++ -std=c++11 -Isingle_include doc/examples/operatorarray__size_type.cpp -o operatorarray__size_type
- Since
- version 1.0.0
Definition at line 21059 of file json.hpp.
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