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◆ operator[]() [3/10]
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 with specified key key.
- Note
- If key is not found in the object, then it is silently added to the object and filled with a
null value to make key a valid reference. In case the value was null before, it is converted to an object.
- Parameters
-
[in] | key | key of the element to access |
- Returns
- reference to the element at key key
- Exceptions
-
std::domain_error | if JSON is not an object or null; example: "cannot use operator[] with string" |
- Complexity
- Logarithmic in the size of the container.
- Example
- The example below shows how object elements can be read and written using the
[] operator. 10 { "one", 1}, { "two", 2}, { "three", 2.9} 14 std::cout << object[ "two"] << "\n\n"; 20 std::cout << std::setw(4) << object << "\n\n"; 26 object[ "five"][ "really"][ "nested"] = true; 29 std::cout << std::setw(4) << object << '\n'; basic_json<> json default JSON class
Output (play with this example online): 2
{
"one": 1,
"three": 3,
"two": 2
}
{
"five": {
"really": {
"nested": true
}
},
"four": null,
"one": 1,
"three": 3,
"two": 2
}
The example code above can be translated withg++ -std=c++11 -Isrc doc/examples/operatorarray__key_type.cpp -o operatorarray__key_type
- See also
- at(const typename object_t::key_type&) for access by reference with range checking
-
value() for access by value with a default value
- Since
- version 1.0.0
Definition at line 3798 of file json.hpp.
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