When you reference a symbol that has not yet been imported, CLion helps you to locate the file (header, as a rule) which contains declaration (definition) of that symbol and adds it to the list of includes.
The import statement is added to the imports section, but the caret does not move from the current position, and your current editing session does not suspend. This feature is known as the Import Assistant.
Import a missing header file
Type a reference to a non-imported class or function.
If there are multiple choices for auto import, select the desired option from the list:
You can configure the auto-import behavior for C/C++ and other languages in.
Show import popup
Suggest creating imports for symbols that lack import statements (enabled by default).
Auto import in completion
Automatically insert an import statement during code completion (enabled by default).
Auto import local files with quotes
Sort the inserted