In Vim how to switch quickly between .h and .cpp files with the same name?

Question

Suppose I have a folder with lots of .h and .cpp files. I frequently need to do the following:

1. open a file prefix_SomeReallyLongFileName.h,

Answer 1

This is just using simple(?!) vimscript, so you can put it into your vimrc, now it works for .c files, but can be modified pretty easily for .cpp (obviously), it even has some "error handling" in the inner if-statements (that is probably pointless), but if anyone needs it, hey, it's there! Without it it's way much shorter (just leave the :e %<.h, for example), so choose whatever you want.

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 == "c"
    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, ".c"], "")

    if filereadable(next_file)
        :e %<.c
    else
        echo join([err_msg, next_file], "")
    endif
endif
endfunction

then add further to your vimrc something along these lines:

let mapleader = "," " 
nnoremap h :call HeaderToggle()

Now whenever you're in normal mode, you press comma , (this is our button) then h and function from the above gets called, and you will toggle between files. Tada!