vimrc: add src-hdr file switching func

.vim/vimrc

@@ -971,6 +971,34 @@ augroup AutoMkdir
 augroup END
 
 
+" as per https://stackoverflow.com/a/38775966
+function! HeaderToggle() " bang for overwrite when saving vimrc
+let file_path = expand('%')
+let file_name = expand('%<')
+let extension = split(file_path, '\.')[-1] " '\.' is how you really split on dot
+let err_msg = 'There is no file '
+
+if extension ==# 'cpp'
+	let next_file = join([file_name, '.h'], '')
+
+	if filereadable(next_file)
+	:e %<.h
+	else
+		echo join([err_msg, next_file], '')
+	endif
+elseif extension ==# 'h'
+	let next_file = join([file_name, '.cpp'], '')
+
+	if filereadable(next_file)
+		:e %<.cpp
+	else
+		echo join([err_msg, next_file], '')
+	endif
+endif
+endfunction
+nnoremap <leader>hh :call HeaderToggle()<cr>
+
+
 nnoremap <Leader>ve :e $MYVIMRC<CR>
 nnoremap <Leader>vr :source $MYVIMRC<CR>