See this thread for the enhanced interoperability with C facility also with a fully worked out illustration and commentary.
But note my point to you earlier was only that a wrapper layer that enables use of some legacy subprograms in modern code can use some tools from the C interoperability facility in the standard even though the wrapper layer and the caller code is in Fortran. So it was about multipurposing a feature, it was not suggesting to anything toward adapting the code for C interoperability. However if you do have to “think about C interoperability soon elsewhere in the code”, just FYI I have posted many examples at this site that you may try to look up.