reference front(); const_reference front() const;
Returns a reference to the first element in the container. For a JSON container #!cpp c
, the expression #!cpp c.front()
is equivalent to #!cpp *c.begin()
.
In case of a structured type (array or object), a reference to the first element is returned. In case of number, string, boolean, or binary values, a reference to the value is returned.
If the JSON value is #!json null
, exception invalid_iterator.214
is thrown.
Strong guarantee: if an exception is thrown, there are no changes in the JSON value.
Constant.
!!! danger
Calling `front` on an empty array or object is undefined behavior and is **guarded by an assertion**!
??? example
The following code shows an example for `front()`. ```cpp --8<-- "examples/front.cpp" ``` Output: ```json --8<-- "examples/front.output" ```