Documentation at https://melpa.org/#/company-c-headers

This library enables the completion of C/C++ header file names using Company. To initialize it, just add it to `company-backends': (add-to-list company-backends company-c-headers) When you type an #include declaration within a supported major mode (see `company-c-headers-modes'), company-c-headers will search for header files within predefined search paths. company-c-headers can search "system" and "user" paths, depending on the type of #include declaration you type. You will probably want to customize the `company-c-headers-path-user and `company-c-headers-path-system variables for your specific needs.