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 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, or boolean 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';
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 withg++ -std=c++11 -Isingle_include doc/examples/back.cpp -o back
- See also
- front() – access the first element
- Since
- version 1.0.0
Definition at line 18183 of file json.hpp.