Most editors have a feature like when you press some keys by placing caret over a function, it pops the documentation of that function along with number and type of arguments that function takes.

I was wondering whether Vim offers such support. For example, while coding in C, I use a built in function qsort(). Since I am not sure about type and number of arguments it takes, I would like to know it without escaping Vim. Is it possible?

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    Not sure this is exactly what you want, but if you give the right value to the option 'keywordprg' (the name of a program which can handle the documentation for the language you want), then by hitting K on a keyword (which can be the name of a function), you should get the info you want. For example, if you install cppman (github.com/aitjcize/cppman) and add an autocmd inside your vimrc such as autocmd FileType cpp setlocal keywordprg=cppman, then cppman should handle the documentation inside a c++ buffer. Not tested though. – saginaw Jan 23 '16 at 18:33
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    @saginaw While cppman is an excellent suggestion, if you have the C and C++ manpages (manpages-posix-dev and libstdc++-X.Y-doc packages on Debian-based systems) installed, plain old man should work. – muru Jan 23 '16 at 23:53

If you can set up YouCompleteMe, it supports C, C++, JavaScript, Go and some other languages. Here's it in action:

enter image description here enter image description here

It's a bit annoying to install, and once it's installed you need to configure it for C and C++ by creating a .ycm_extra_conf.py. I lifted one from this repo, and got this effect.

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    "t's a bit annoying to install,"... That's an understatement. Still, it is very good. ^_~ – Sardathrion - against SE abuse Jan 28 '16 at 9:27
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    Is there any way to force the completions pop-up to remain opened while the function arguments are typed? For example, as soon as you type the first letter of the first argument qsort(a, the pop-up window disappears, making it difficult to remember the next arguments. – thiagowfx Jun 28 '16 at 21:02
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    But it just shows the prototype of the function. How to make it show its doxygen comments (like Eclipse does with javadocs)? I mean parameters, output, notes, refs... – Zeta.Investigator Apr 13 '18 at 8:33
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    @Zeta.Investigator One thing I use heavily in Python is YcmCompleter GoTo, which usually sends you to where the function/class was defined in code. That is the line just above the docstring, which lists everything you asked for. I am not sure if the inline commenting is in the same place in C/Java/C++. – user1717828 Mar 19 '19 at 17:58

For C, pressing K on the keyword will pull up the built-in manpage directly. For instance, place the cursor on the printf keyword:

printf("Hello, %s!", foo);

Now press K (upper case K) and the manpage for printf should appear in VIM:

   printf - format and print data

   printf FORMAT [ARGUMENT]...
   printf OPTION

   Print ARGUMENT(s) according to FORMAT, or execute according to OPTION:

   --help display this help and exit

          output version information and exit

   FORMAT controls the output as in C printf.  Interpreted sequences are:

   \"     double quote
   \\     backslash

   ... It continues for quite a few scrollable pages

This seems to work out of the box in all Debian-derived distros that I've tried it on, no specific configuration required.

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    That's the manpage of printf(1) the command, not printf(3) the function. In any case, the C function manpages are from manpages-dev, which is usually installed by default, but not always, and POSIX functions are in manpages-posix-dev - usually not installed by default, neither is C++ documentation (libstdc++-X.Y-doc). – muru Jan 24 '16 at 9:24

If you want proper documentation, the plugin in saginaw's comment seems to cover your C++ needs. I don't know of a generic one but you can probably find alternatives for other languages on vim.org.


  • your code is already indexed with ctags,
  • your index also includes the standard library,
  • and all you want is a hint,

you can use <C-w>} to open the definition of the keyword under your cursor in a preview window. YMMV, of course.

See :help preview-window, :help tags and :help ctags.

You can also use Vim's built-in "include-search" functionality: press [i to print the "signature" of the word under the cursor in the command-line:


See :help include-search.

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    [i is weird. It works for stdlib.h and qsort, but not cstdlib and std::qsort or just qsort. – muru Jan 23 '16 at 20:25
  • For those unfamiliar with the nomenclature as I am/was <C-w> means CTRL-W Which is the nomenclature used in the :help files. You may then use :pc to close the preview window. – danielson317 Nov 21 '19 at 16:49

Vim's C/C++ file type comes with a decent omnicompletion function, which supports "preview" functionality. So add "preview" to your completeopt option and see a function signature when you do insert mode completion.

In normal mode, you could CTRL+W } to open the function declaration in the preview window manually.

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As mentioned pressing K on the keyword works by searching a man page. For getting C++ man pages you may try https://github.com/aitjcize/cppman (it gets "man pages" from cplusplus.com and cppreference.com).

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Install YouCompleteMe. When you place the cursor over an identifier, enter YcmCompleter GetDoc command to get the doc in a little preview window at the bottom. It works across many languages like python and c/c++.

Youcompleteme also displays the preview window during its autocomplete feature. You can customize the behavior of the doc preview with g:ycm_autoclose_preview_window_after_completion variable.

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