Vim for C Programmers

Exuberant ctags (see the on-line Resources) is an external program that can generate tags for Vim to navigate source code. If all of your source code is contained in only one directory, simply go to the directory in the shell and enter:

$ ctags .

This generates a tags file called tags. Vim reads this file for jumping to functions, enums, #defines and other C constructs.

If the source code is distributed across several directories, ctags has to generate tags for all of them relative to a certain directory. To do this, go to the root directory of the source code and execute:

$ ctags -R .

Check whether the tags file has been generated. You also can open and read the tags file in Vim.

Now, let us move on to navigating the source code using tags. Navigating the source code using ctags is one of the most fascinating tools that a programmer has. You can read the code so nicely and quickly that you wonder how it would have been without ctags.

Once the tags file has been generated, open the file in Vim as normal, except that if the file is deep inside, open it from the root directory. For instance, your source code is organized like this:

  common
    |
    ----> gui --> wxpython
    |       |
    |       ------>Tk
    |
    ----> backend --> networking

  include

  user

If you want to edit tcp.c under the common/backend/networking directory, you should open it like this:

$ vim common/backend/networking/tcp.c

instead of like this:

$ cd common/backend/networking

and:

$ vim tcp.c

The tags file is situated in the directory above common, and Vim automatically knows the location of the tags file this way.

Alternatively, you can open the file using the second method mentioned above and execute this from inside of Vim:

:se tags=../../../tags

The first method is easier for navigation. Once you open the file, you can jump from one function definition to another easily by using the key combination Ctrl-].

If you want to go to the definition of anything, be it a function, macro or anything else, simply press Ctrl-] when the cursor is positioned on it. Thus, from invocation, we can move to the definition. It takes you there no matter which file contains it. Assuming that we call drawscreen() from tcp.c, it automatically takes you there, even if the file is contained under common/gui.

If you want to go back to what you were reading, press Ctrl-T, and you return to where you left. You can jump to another invocation from there by pressing Ctrl-] again. You can continue this process ad infinitum, and you can keep coming back by pressing Ctrl-T.

Another way to find a function definition if you know only a part of the name is:

:ta /function

This command takes you to the first match if there are multiple matches. You can go to the next match with :tn.

If there are multiple definitions and you want to choose among them, you can press G Ctrl-] or type :tselect <tagname>. This way you can modify the source code by navigating with tags without even knowing which file contains what.

Cscope is another powerful source code navigation tool with which we can perform a variety of searches. Here is a sample output of the Cscope menu:

Find this C symbol:
Find this global definition:
Find functions called by this function:
Find functions calling this function:
Find this text string:
Change this text string:
Find this egrep pattern:
Find this file:
Find files #including this file:

Now, Vim has integrated Cscope into its repertoire, making it convenient for programmers to use the same features in Cscope from the cool comfort of Vim. All you have to do is establish a Cscope connection by issuing :cs add cscope.out.

As we discussed before with ctags, Cscope generates an index called cscope.out that can be generated by using the shell command:

$ cscope -Rbq 

This generates the file cscope.out. It is to be executed from the source code root directory à lá Ctags. You then open the file as before, relative to the source code root directory, and make a Cscope connection with the command :cs add cscope.out. You can verify existing Cscope connections by typing :cs show.

. What you can search for from inside of Vim can be seen using :cs<CR>. For instance, to go to a particular file, or a header of a source file, simply type :cs f f stdio.h for opening stdio.h or :cs f f foo.c.

For searching for functions called by a function foo.c, type :cs f d foo.c. This lists out the functions called by foo.c. For functions calling foo.c, type :cs f c foo.c.

To search for an egrep pattern, type :cs f e varName and so on. For a list of the available options, type :cs. It displays a range of available options.

Now, if you have both ctags and Cscope, you can type :cstag /foo to search for a function or enum or whatever that contains foo.