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Niels Lohmann
172eba6e46
Add See also links in both directions between the concept pages (features, home, integration) and the API pages, write API links in code font, give every entry a comment after a dash, and show the callback event figure on the parser callbacks page. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
1.5 KiB
1.5 KiB
nlohmann::basic_json::front
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 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- to access the last elementbasic_json_view::front- the same access on a zero-copy view (document order, not sorted; duplicate keys are visited)- Element Access - overview of all ways to access elements
Version history
- Added in version 1.0.0.
- Binary values are supported since version 3.8.0.