How to convert C89 style comments to C99

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Three regexp replace operations in Vim suffice to convert C89 into C99/C++ style comments.

1. Remove */
%s/\*\///
2. Replace /* by //
%s/\/\*/\/\//
3. Replace <SPACE>*<SPACE> by //<SPACE>
%s/ \* /\/\/ /

You can put that inside a function in your home .vimrc file if you need to refactor several source files:

" CONVERT C89 TO C99 COMMENTS                                                                                                        
func! C89toC99()                                                                                                                     
         %s/\*\///                                                                                                                    
         %s/\/\*/\/\//                                                                                                                
         %s/ \* /\/\/ /
endfunc

And then invoke it in vim:

call C89toC99()

Despite it is not a fully tested conversion method (it will let some blank lines here and there and it might not capture all your inner * characters it will still likely save you 95% of the required time to do the change manually.