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◆ back() [2/2]
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 >::back |
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Returns a reference to the last element in the container. For a JSON container c , the expression c.back() is equivalent to auto tmp = c.end();
--tmp;
return *tmp;
- Returns
- In case of a structured type (array or object), a reference to the last element is returned. In case of number, string, boolean, or binary values, a reference to the value is returned.
- Complexity
- Constant.
- Precondition
- The JSON value must not be
null (would throw std::out_of_range ) or an empty array or object (undefined behavior, guarded by assertions).
- Postcondition
- The JSON value remains unchanged.
- Exceptions
-
invalid_iterator.214 | when called on a null value. See example below. |
- Example
- The following code shows an example for
back() .
2#include <nlohmann/json.hpp>
10 json j_number_integer = 17;
11 json j_number_float = 23.42;
12 json j_object = {{ "one", 1}, { "two", 2}};
13 json j_object_empty(json::value_t::object);
14 json j_array = {1, 2, 4, 8, 16};
15 json j_array_empty(json::value_t::array);
16 json j_string = "Hello, world";
19 std::cout << j_boolean.back() << '\n';
20 std::cout << j_number_integer.back() << '\n';
21 std::cout << j_number_float.back() << '\n';
22 std::cout << j_object.back() << '\n';
24 std::cout << j_array.back() << '\n';
26 std::cout << j_string.back() << '\n';
36 std::cout << e.what() << '\n';
detail::invalid_iterator invalid_iterator exception indicating errors with iterators
basic_json<> json default JSON class
Output (play with this example online): true
17
23.42
2
16
"Hello, world"
[json.exception.invalid_iterator.214] cannot get value
The example code above can be translated with g++ -std=c++11 -Isingle_include doc/examples/back.cpp -o back
- See also
- see front() – access the first element
- Since
- version 1.0.0
Definition at line 21680 of file json.hpp.
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