# nlohmann::basic_json::front ```cpp 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()`. ## Return value In the case of a structured type (array or object), a reference to the first 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 `#!json null`, exception [`invalid_iterator.214`](../../home/exceptions.md#jsonexceptioninvalid_iterator214) is thrown. ## Complexity Constant. ## Notes !!! info "Precondition" The array or object must not be empty. Calling `front` on an empty array or object yields undefined behavior. ## Examples ??? example The following code shows an example for `front()`. ```cpp --8<-- "examples/front.cpp" ``` Output: ```json --8<-- "examples/front.output" ``` ## See also - [back](back.md) to access the last element ## Version history - Added in version 1.0.0. - Adjusted code to return reference to binary values in version 3.8.0.