mirror of
https://github.com/nlohmann/json.git
synced 2025-05-11 21:53:56 +00:00
29cd970b94
* 🔥 consolidate documentation * ♻️ overwork std specializations * 🚚 move images files to mkdocs * ♻️ fix URLs * 🔧 tweak MkDocs configuration * 🔧 add namespaces * 📝 document deprecations * 📝 document documentation generation * 🚸 improve search * 🚸 add examples * 🚧 start adding documentation for macros * 📝 add note for https://github.com/nlohmann/json/issues/874#issuecomment-1001699139 * 📝 overwork example handling * 📝 fix Markdown tables
1.3 KiB
1.3 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 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.
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
!!! danger
Calling `front` on an empty array or object is undefined behavior and is **guarded by an assertion**!
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 element
Version history
- Added in version 1.0.0.
- Adjusted code to return reference to binary values in version 3.8.0.