Jump to function definition

Use ctags. Generate a tags file, and tell vim where it is using the :tags command. Then you can just jump to the function definition using Ctrl-]

There are more tags tricks and tips in this question.

If everything is contained in one file, there's the command gd (as in 'goto definition'), which will take you to the first occurrence in the file of the word under the cursor, which is often the definition.

Use gd or gD while placing the cursor on any variable in your program.

1. gd will take you to the local declaration.
2. gD will take you to the global declaration.

more navigation options can be found in here.

Use cscope for cross referencing large project such as the linux kernel.

TL;DR:

You can do this using internal VIM functionality but a modern (and much easier) way is to use COC for intellisense-like completion and one or more language servers (LS) for jump-to-definition (and way way more). For even more functionality (but it's not needed for jump-to-definition) you can install one or more debuggers and get a full blown IDE experience.

Best second is to use native VIM's functionality called define-search but it was invented for C preprocessor's #define directive and for most other languages requires extra configuration, for some isn't possible at all (also you miss on other IDE features). Finally, a fallback to that is ctags.

Quick-start:

1. install vim-plug to manage your VIM plug-ins
2. add COC and (optionally) Vimspector at the top of ~/.vimrc:

   call plug#begin()
   Plug 'neoclide/coc.nvim', {'branch': 'release'}
   Plug 'puremourning/vimspector'
   call plug#end()
   
   " key mappings example
   nmap <silent> gd <Plug>(coc-definition)
   nmap <silent> gD <Plug>(coc-implementation)
   nmap <silent> gr <Plug>(coc-references)
   " there's way more, see `:help coc-key-mappings@en'
   

3. call :source $MYVIMRC | PlugInstall to reload VIM config and download plug-ins
4. restart vim and call :CocInstall coc-marketplace to get easy access to COC extensions
5. call :CocList marketplace and search for language servers, e.g.:

• type python to find coc-jedi,
• type php to find coc-phpls, etc.

6. (optionally) see :h VimspectorInstall to install additional debuggers, e.g.:

• :VimspectorInstall debugpy,
• :VimspectorInstall vscode-php-debug, etc.

Full story:

Language server (LS) is a separate standalone application (one for each programming language) that runs in the background and analyses your whole project in real time exposing extra capabilities to your editor (any editor, not only vim). You get things like:

• namespace aware tag completion
• jump to definition
• jump to next / previous error
• find all references to an object
• find all interface implementations
• rename across a whole project
• documentation on hover
• snippets, code actions, formatting, linting and more...

Communication with language servers takes place via Language Server Protocol (LSP). Both nvim and vim8 (or higher) support LSP through plug-ins, the most popular being Conquer of Completion (COC).

List of actively developed language servers and their capabilities is available on Lang Server website. Not all of those are provided by COC extensions. If you want to use one of those you can either write a COC extension yourself or install LS manually and use the combo of following VIM plug-ins as alternative to COC:

• LanguageClient - handles LSP
• deoplete - triggers completion as you type

Communication with debuggers takes place via Debug Adapter Protocol (DAP). The most popular DAP plug-in for VIM is Vimspector.

Language Server Protocol (LSP) was created by Microsoft for Visual Studio Code and released as an open source project with a permissive MIT license (standardized by collaboration with Red Hat and Codenvy). Later on Microsoft released Debug Adapter Protocol (DAP) as well. Any language supported by VSCode is supported in VIM.

I personally recommend using COC + language servers provided by COC extensions + ALE for extra linting (but with LSP support disabled to avoid conflicts with COC) + Vimspector + debuggers provided by Vimspector (called "gadgets") + following VIM plug-ins:

call plug#begin()
Plug 'neoclide/coc.nvim'
Plug 'dense-analysis/ale'
Plug 'puremourning/vimspector'
Plug 'scrooloose/nerdtree'
Plug 'scrooloose/nerdcommenter'
Plug 'sheerun/vim-polyglot'
Plug 'yggdroot/indentline'
Plug 'tpope/vim-surround'
Plug 'kana/vim-textobj-user'
  \| Plug 'glts/vim-textobj-comment'
Plug 'janko/vim-test'
Plug 'vim-scripts/vcscommand.vim'
Plug 'mhinz/vim-signify'
call plug#end()

You can google each to see what they do.

Native VIM jump to definition:

If you really don't want to use Language Server and still want a somewhat decent jump to definition with native VIM you should get familiar with :ij and :dj which stand for include-jump and definition-jump. These VIM commands let you jump to any file that's included by your project or jump to any defined symbol that's in any of the included files. For that to work, however, VIM has to know how lines that include files or define symbols look like in any given language. You can set it up per language in ~/.vim/ftplugin/$file_type.vim with set include=$regex and set define=$regex patterns as described in :h include-search, although, coming up with those patterns is a bit of an art and sometimes not possible at all, e.g. for languages where symbol definition or file import can span over multiple lines (e.g. Golang). If that's your case the usual fallback is ctags as described in other answers.

As Paul Tomblin mentioned you have to use ctags. You could also consider using plugins to select appropriate one or to preview the definition of the function under cursor. Without plugins you will have a headache trying to select one of the hundreds overloaded 'doAction' methods as built in ctags support doesn't take in account the context - just a name.

Also you can use cscope and its 'find global symbol' function. But your vim have to be compiled with +cscope support which isn't default one option of build.

If you know that the function is defined in the current file, you can use 'gD' keystrokes in a normal mode to jump to definition of the symbol under cursor.

Here is the most downloaded plugin for navigation
http://www.vim.org/scripts/script.php?script_id=273

Here is one I've written to select context while jump to tag
http://www.vim.org/scripts/script.php?script_id=2507

Another common technique is to place the function name in the first column. This allows the definition to be found with a simple search.

int
main(int argc, char *argv[])
{
    ...
}

The above function could then be found with /^main inside the file or with :grep -r '^main' *.c in a directory. As long as code is properly indented the only time the identifier will occur at the beginning of a line is at the function definition.

Of course, if you aren't using ctags from this point on you should be ashamed of yourself! However, I find this coding standard a helpful addition as well.

1- install exuberant ctags. If you're using osx, this article shows a little trick: http://www.runtime-era.com/2012/05/exuberant-ctags-in-osx-107.html

2- If you only wish to include the ctags for the files in your directory only, run this command in your directory:

ctags -R

This will create a "tags" file for you.

3- If you're using Ruby and wish to include the ctags for your gems (this has been really helpful for me with RubyMotion and local gems that I have developed), do the following:

ctags --exclude=.git --exclude='*.log' -R * `bundle show --paths`

credit: https://coderwall.com/p/lv1qww (Note that I omitted the -e option which generates tags for emacs instead of vim)

4- Add the following line to your ~/.vimrc

set autochdir 
set tags+=./tags;

(Why the semi colon: http://vim.wikia.com/wiki/Single_tags_file_for_a_source_tree )

5- Go to the word you'd like to follow and hit ctrl + ] ; if you'd like to go back, use ctrl+o (source: https://stackoverflow.com/a/53929/226255)

To second Paul's response: yes, ctags (especially exuberant-ctags (http://ctags.sourceforge.net/)) is great. I have also added this to my vimrc, so I can use one tags file for an entire project:

set tags=tags;/

After generating ctags, you can also use the following in vim:

:tag <f_name>

Above will take you to function definition.