nlohmann::basic_json::back¶

referenceback();
const_referenceback()const;

Returns a reference to the last element in the container. For a JSON container c, the expression c.back() is equivalent to

autotmp=c.end();
--tmp;
return*tmp;

Return value¶

In the case of a structured type (array or object), a reference to the last element is returned. In the case of number, string, boolean, or binary values, a reference to the value is returned.

Exception safety¶

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

Exceptions¶

If the JSON value is null, exception invalid_iterator.214 is thrown.

Complexity¶

Constant.

Notes¶

Precondition

The array or object must not be empty. Calling back on an empty array or object yields undefined behavior.

Examples¶

Example

The following code shows an example for back().

#include<iostream>
#include<nlohmann/json.hpp>
usingjson=nlohmann::json;
intmain()
{
// create JSON values
jsonj_boolean=true;
jsonj_number_integer=17;
jsonj_number_float=23.42;
jsonj_object={{"one",1},{"two",2}};
jsonj_object_empty(json::value_t::object);
jsonj_array={1,2,4,8,16};
jsonj_array_empty(json::value_t::array);
jsonj_string="Hello, world";
// call back()
std::cout<<j_boolean.back()<<'\n';
std::cout<<j_number_integer.back()<<'\n';
std::cout<<j_number_float.back()<<'\n';
std::cout<<j_object.back()<<'\n';
//std::cout << j_object_empty.back() << '\n'; // undefined behavior
std::cout<<j_array.back()<<'\n';
//std::cout << j_array_empty.back() << '\n'; // undefined behavior
std::cout<<j_string.back()<<'\n';
// back() called on a null value
try
{
jsonj_null;
j_null.back();
}
catch(constjson::invalid_iterator&e)
{
std::cout<<e.what()<<'\n';
}
}

Output:

true
17
23.42
2
16
"Hello, world"
[json.exception.invalid_iterator.214]cannotgetvalue

Version history¶

Added in version 1.0.0.
Adjusted code to return reference to binary values in version 3.8.0.