:h usr_30.txt

usr_30.txt For Vim version 7.4. Last change: 2007 Nov 10LINK

VIM USER MANUAL - by Bram Moolenaar

Editing programs

Vim has various commands that aid in writing computer programs. Compile a

program and directly jump to reported errors. Automatically set the indent

for many languages and format comments.

30.1 Compiling

30.2 Indenting C files

30.3 Automatic indenting

30.4 Other indenting

30.5 Tabs and spaces

30.6 Formatting comments

Next chapter: usr_31.txt Exploiting the GUI

Previous chapter: usr_29.txt Moving through programs

Table of contents: usr_toc.txt

==============================================================================

30.1 CompilingLINK

Vim has a set of so called "quickfix" commands. They enable you to compile a

program from within Vim and then go through the errors generated and fix them

(hopefully). You can then recompile and fix any new errors that are found

until finally your program compiles without any error.

The following command runs the program "make" (supplying it with any argument

you give) and captures the results:

:make {arguments}

If errors were generated, they are captured and the editor positions you where

the first error occurred.

Take a look at an example ":make" session. (Typical :make sessions generate

far more errors and fewer stupid ones.) After typing ":make" the screen looks

like this:

:!make | &tee /tmp/vim215953.err

gcc -g -Wall -o prog main.c sub.c

main.c: In function 'main':

main.c:6: too many arguments to function 'do_sub'

main.c: At top level:

main.c:10: parse error before '}'

make: *** [prog] Error 1

2 returned

"main.c" 11L, 111C

(3 of 6): too many arguments to function 'do_sub'

Press ENTER or type command to continue

From this you can see that you have errors in the file "main.c". When you

press <Enter>, Vim displays the file "main.c", with the cursor positioned on

line 6, the first line with an error. You did not need to specify the file or

the line number, Vim knew where to go by looking in the error messages.

+---------------------------------------------------+

|int main() |

|{ |

| int i=3; |

cursor -> | do_sub("foo"); |

| ++i; |

| return (0); |

|} |

| ~ |

|(3 of 12): too many arguments to function 'do_sub' |

+---------------------------------------------------+

The following command goes to where the next error occurs:

:cnext

Vim jumps to line 10, the last line in the file, where there is an extra '}'.

When there is not enough room, Vim will shorten the error message. To see

the whole message use:

:cc

You can get an overview of all the error messages with the ":clist" command.

The output looks like this:

:clist

3 main.c: 6:too many arguments to function 'do_sub'

5 main.c: 10:parse error before '}'

Only the lines where Vim recognized a file name and line number are listed

here. It assumes those are the interesting lines and the rest is just boring

messages. However, sometimes unrecognized lines do contain something you want

to see. Output from the linker, for example, about an undefined function.

To see all the messages add a "!" to the command:

:clist!

1 gcc -g -Wall -o prog main.c sub.c

2 main.c: In function 'main':

3 main.c:6: too many arguments to function 'do_sub'

4 main.c: At top level:

5 main.c:10: parse error before '}'

6 make: *** [prog] Error 1

Vim will highlight the current error. To go back to the previous error, use:

:cprevious

Other commands to move around in the error list:

:cfirst to first error

:clast to last error

:cc 3 to error nr 3

USING ANOTHER COMPILER

The name of the program to run when the ":make" command is executed is defined

by the 'makeprg' option. Usually this is set to "make", but Visual C++ users

should set this to "nmake" by executing the following command:

:set makeprg=nmake

You can also include arguments in this option. Special characters need to

be escaped with a backslash. Example:

:set makeprg=nmake\ -f\ project.mak

You can include special Vim keywords in the command specification. The %

character expands to the name of the current file. So if you execute the

command:

:set makeprg=make\ %:S

When you are editing main.c, then ":make" executes the following command:

make main.c

This is not too useful, so you will refine the command a little and use the :r

(root) modifier:

:set makeprg=make\ %:r:S.o

Now the command executed is as follows:

make main.o

More about these modifiers here: filename-modifiers.

OLD ERROR LISTS

Suppose you ":make" a program. There is a warning message in one file and an

error message in another. You fix the error and use ":make" again to check if

it was really fixed. Now you want to look at the warning message. It doesn't

show up in the last error list, since the file with the warning wasn't

compiled again. You can go back to the previous error list with:

:colder

Then use ":clist" and ":cc {nr}" to jump to the place with the warning.

To go forward to the next error list:

:cnewer

Vim remembers ten error lists.

SWITCHING COMPILERS

You have to tell Vim what format the error messages are that your compiler

produces. This is done with the 'errorformat' option. The syntax of this

option is quite complicated and it can be made to fit almost any compiler.

You can find the explanation here: errorformat.

You might be using various different compilers. Setting the 'makeprg' option,

and especially the 'errorformat' each time is not easy. Vim offers a simple

method for this. For example, to switch to using the Microsoft Visual C++

compiler:

:compiler msvc

This will find the Vim script for the "msvc" compiler and set the appropriate

options.

You can write your own compiler files. See write-compiler-plugin.

OUTPUT REDIRECTION

The ":make" command redirects the output of the executed program to an error

file. How this works depends on various things, such as the 'shell'. If your

":make" command doesn't capture the output, check the 'makeef' and

'shellpipe' options. The 'shellquote' and 'shellxquote' options might also

matter.

In case you can't get ":make" to redirect the file for you, an alternative is

to compile the program in another window and redirect the output into a file.

Then have Vim read this file with:

:cfile {filename}

Jumping to errors will work like with the ":make" command.

==============================================================================

30.2 Indenting C style textLINK

A program is much easier to understand when the lines have been properly

indented. Vim offers various ways to make this less work. For C or C style

programs like Java or C++, set the 'cindent' option. Vim knows a lot about C

programs and will try very hard to automatically set the indent for you. Set

the 'shiftwidth' option to the amount of spaces you want for a deeper level.

Four spaces will work fine. One ":set" command will do it:

:set cindent shiftwidth=4

With this option enabled, when you type something such as "if (x)", the next

line will automatically be indented an additional level.

if (flag)

Automatic indent ---> do_the_work();

Automatic unindent <-- if (other_flag) {

Automatic indent ---> do_file();

keep indent do_some_more();

Automatic unindent <-- }

When you type something in curly braces ({}), the text will be indented at the

start and unindented at the end. The unindenting will happen after typing the

'}', since Vim can't guess what you are going to type.

One side effect of automatic indentation is that it helps you catch errors in

your code early. When you type a } to finish a function, only to find that

the automatic indentation gives it more indent than what you expected, there

is probably a } missing. Use the "%" command to find out which { matches the

} you typed.

A missing ) and ; also cause extra indent. Thus if you get more white

space than you would expect, check the preceding lines.

When you have code that is badly formatted, or you inserted and deleted lines,

you need to re-indent the lines. The "=" operator does this. The simplest

form is:

This indents the current line. Like with all operators, there are three ways

to use it. In Visual mode "=" indents the selected lines. A useful text

object is "a{". This selects the current {} block. Thus, to re-indent the

code block the cursor is in:

=a{

I you have really badly indented code, you can re-indent the whole file with:

gg=G

However, don't do this in files that have been carefully indented manually.

The automatic indenting does a good job, but in some situations you might want

to overrule it.

SETTING INDENT STYLE

Different people have different styles of indentation. By default Vim does a

pretty good job of indenting in a way that 90% of programmers do. There are

different styles, however; so if you want to, you can customize the

indentation style with the 'cinoptions' option.

By default 'cinoptions' is empty and Vim uses the default style. You can

add various items where you want something different. For example, to make

curly braces be placed like this:

if (flag)

{

i = 8;

j = 0;

}

Use this command:

:set cinoptions+={2

There are many of these items. See cinoptions-values.

==============================================================================

30.3 Automatic indentingLINK

You don't want to switch on the 'cindent' option manually every time you edit

a C file. This is how you make it work automatically:

:filetype indent on

Actually, this does a lot more than switching on 'cindent' for C files. First

of all, it enables detecting the type of a file. That's the same as what is

used for syntax highlighting.

When the filetype is known, Vim will search for an indent file for this

type of file. The Vim distribution includes a number of these for various

programming languages. This indent file will then prepare for automatic

indenting specifically for this file.

If you don't like the automatic indenting, you can switch it off again:

:filetype indent off

If you don't like the indenting for one specific type of file, this is how you

avoid it. Create a file with just this one line:

:let b:did_indent = 1

Now you need to write this in a file with a specific name:

{directory}/indent/{filetype}.vim

The {filetype} is the name of the file type, such as "cpp" or "java". You can

see the exact name that Vim detected with this command:

:set filetype

In this file the output is:

filetype=help

Thus you would use "help" for {filetype}.

For the {directory} part you need to use your runtime directory. Look at

the output of this command:

set runtimepath

Now use the first item, the name before the first comma. Thus if the output

looks like this:

runtimepath=~/.vim,/usr/local/share/vim/vim60/runtime,~/.vim/after

You use "~/.vim" for {directory}. Then the resulting file name is:

~/.vim/indent/help.vim

Instead of switching the indenting off, you could write your own indent file.

How to do that is explained here: indent-expression.

==============================================================================

30.4 Other indentingLINK

The most simple form of automatic indenting is with the 'autoindent' option.

It uses the indent from the previous line. A bit smarter is the 'smartindent'

option. This is useful for languages where no indent file is available.

'smartindent' is not as smart as 'cindent', but smarter than 'autoindent'.

With 'smartindent' set, an extra level of indentation is added for each {

and removed for each }. An extra level of indentation will also be added for

any of the words in the 'cinwords' option. Lines that begin with # are

treated specially: all indentation is removed. This is done so that

preprocessor directives will all start in column 1. The indentation is

restored for the next line.

CORRECTING INDENTS

When you are using 'autoindent' or 'smartindent' to get the indent of the

previous line, there will be many times when you need to add or remove one

'shiftwidth' worth of indent. A quick way to do this is using the CTRL-D and

CTRL-T commands in Insert mode.

For example, you are typing a shell script that is supposed to look like

this:

if test -n a; then

echo a

echo "-------"

Start off by setting these options:

:set autoindent shiftwidth=3

You start by typing the first line, <Enter> and the start of the second line:

if test -n a; then

echo

Now you see that you need an extra indent. Type CTRL-T. The result:

if test -n a; then

echo

The CTRL-T command, in Insert mode, adds one 'shiftwidth' to the indent, no

matter where in the line you are.

You continue typing the second line, <Enter> and the third line. This time

the indent is OK. Then <Enter> and the last line. Now you have this:

if test -n a; then

echo a

echo "-------"

To remove the superfluous indent in the last line press CTRL-D. This deletes

one 'shiftwidth' worth of indent, no matter where you are in the line.

When you are in Normal mode, you can use the ">>" and "<<" commands to

shift lines. ">" and "<" are operators, thus you have the usual three ways to

specify the lines you want to indent. A useful combination is:

>i{

This adds one indent to the current block of lines, inside {}. The { and }

lines themselves are left unmodified. ">a{" includes them. In this example

the cursor is on "printf":

original text after ">i{" after ">a{"

if (flag) if (flag) if (flag)

{ { {

printf("yes"); printf("yes"); printf("yes");

flag = 0; flag = 0; flag = 0;

} } }

==============================================================================

30.5 Tabs and spacesLINK

'tabstop' is set to eight by default. Although you can change it, you quickly

run into trouble later. Other programs won't know what tabstop value you

used. They probably use the default value of eight, and your text suddenly

looks very different. Also, most printers use a fixed tabstop value of eight.

Thus it's best to keep 'tabstop' alone. (If you edit a file which was written

with a different tabstop setting, see 25.3 for how to fix that.)

For indenting lines in a program, using a multiple of eight spaces makes

you quickly run into the right border of the window. Using a single space

doesn't provide enough visual difference. Many people prefer to use four

spaces, a good compromise.

Since a <Tab> is eight spaces and you want to use an indent of four spaces,

you can't use a <Tab> character to make your indent. There are two ways to

handle this:

1. Use a mix of <Tab> and space characters. Since a <Tab> takes the place of

eight spaces, you have fewer characters in your file. Inserting a <Tab>

is quicker than eight spaces. Backspacing works faster as well.

2. Use spaces only. This avoids the trouble with programs that use a

different tabstop value.

Fortunately, Vim supports both methods quite well.

SPACES AND TABS

If you are using a combination of tabs and spaces, you just edit normally.

The Vim defaults do a fine job of handling things.

You can make life a little easier by setting the 'softtabstop' option.

This option tells Vim to make the <Tab> key look and feel as if tabs were set

at the value of 'softtabstop', but actually use a combination of tabs and

spaces.

After you execute the following command, every time you press the <Tab> key

the cursor moves to the next 4-column boundary:

:set softtabstop=4

When you start in the first column and press <Tab>, you get 4 spaces inserted

in your text. The second time, Vim takes out the 4 spaces and puts in a <Tab>

(thus taking you to column 8). Thus Vim uses as many <Tab>s as possible, and

then fills up with spaces.

When backspacing it works the other way around. A <BS> will always delete

the amount specified with 'softtabstop'. Then <Tab>s are used as many as

possible and spaces to fill the gap.

The following shows what happens pressing <Tab> a few times, and then using

<BS>. A "." stands for a space and "------->" for a <Tab>.

type result

<Tab> ....

<Tab><Tab><Tab> ------->....

<Tab><Tab><Tab><BS><BS> ....

An alternative is to use the 'smarttab' option. When it's set, Vim uses

'shiftwidth' for a <Tab> typed in the indent of a line, and a real <Tab> when

typed after the first non-blank character. However, <BS> doesn't work like

with 'softtabstop'.

JUST SPACES

If you want absolutely no tabs in your file, you can set the 'expandtab'

option:

:set expandtab

When this option is set, the <Tab> key inserts a series of spaces. Thus you

get the same amount of white space as if a <Tab> character was inserted, but

there isn't a real <Tab> character in your file.

The backspace key will delete each space by itself. Thus after typing one

<Tab> you have to press the <BS> key up to eight times to undo it. If you are

in the indent, pressing CTRL-D will be a lot quicker.

CHANGING TABS IN SPACES (AND BACK)

Setting 'expandtab' does not affect any existing tabs. In other words, any

tabs in the document remain tabs. If you want to convert tabs to spaces, use

the ":retab" command. Use these commands:

:set expandtab

:%retab

Now Vim will have changed all indents to use spaces instead of tabs. However,

all tabs that come after a non-blank character are kept. If you want these to

be converted as well, add a !:

:%retab!

This is a little bit dangerous, because it can also change tabs inside a

string. To check if these exist, you could use this:

/"[^"\t]*\t[^"]*"

It's recommended not to use hard tabs inside a string. Replace them with

"\t" to avoid trouble.

The other way around works just as well:

:set noexpandtab

:%retab!

==============================================================================

30.6 Formatting commentsLINK

One of the great things about Vim is that it understands comments. You can

ask Vim to format a comment and it will do the right thing.

Suppose, for example, that you have the following comment:

* This is a test

* of the text formatting.

You then ask Vim to format it by positioning the cursor at the start of the

comment and type:

gq]/

"gq" is the operator to format text. "]/" is the motion that takes you to the

end of a comment. The result is:

* This is a test of the text formatting.

Notice that Vim properly handled the beginning of each line.

An alternative is to select the text that is to be formatted in Visual mode

and type "gq".

To add a new line to the comment, position the cursor on the middle line and

press "o". The result looks like this:

* This is a test of the text formatting.

Vim has automatically inserted a star and a space for you. Now you can type

the comment text. When it gets longer than 'textwidth', Vim will break the

line. Again, the star is inserted automatically:

* This is a test of the text formatting.

* Typing a lot of text here will make Vim

* break

For this to work some flags must be present in 'formatoptions':

r insert the star when typing <Enter> in Insert mode

o insert the star when using "o" or "O" in Normal mode

c break comment text according to 'textwidth'

See fo-table for more flags.

DEFINING A COMMENT

The 'comments' option defines what a comment looks like. Vim distinguishes

between a single-line comment and a comment that has a different start, end

and middle part.

Many single-line comments start with a specific character. In C++ // is

used, in Makefiles #, in Vim scripts ". For example, to make Vim understand

C++ comments:

:set comments=://

The colon separates the flags of an item from the text by which the comment is

recognized. The general form of an item in 'comments' is:

{flags}:{text}

The {flags} part can be empty, as in this case.

Several of these items can be concatenated, separated by commas. This

allows recognizing different types of comments at the same time. For example,

let's edit an e-mail message. When replying, the text that others wrote is

preceded with ">" and "!" characters. This command would work:

:set comments=n:>,n:!

There are two items, one for comments starting with ">" and one for comments

that start with "!". Both use the flag "n". This means that these comments

nest. Thus a line starting with ">" may have another comment after the ">".

This allows formatting a message like this:

> ! Did you see that site?

> ! It looks really great.

> I don't like it. The

> colors are terrible.

What is the URL of that

site?

Try setting 'textwidth' to a different value, e.g., 80, and format the text by

Visually selecting it and typing "gq". The result is:

> ! Did you see that site? It looks really great.

> I don't like it. The colors are terrible.

What is the URL of that site?

You will notice that Vim did not move text from one type of comment to

another. The "I" in the second line would have fit at the end of the first

line, but since that line starts with "> !" and the second line with ">", Vim

knows that this is a different kind of comment.

A THREE PART COMMENT

A C comment starts with "/*", has "*" in the middle and "*/" at the end. The

entry in 'comments' for this looks like this:

:set comments=s1:/*,mb:*,ex:*/

The start is defined with "s1:/*". The "s" indicates the start of a

three-piece comment. The colon separates the flags from the text by which the

comment is recognized: "/*". There is one flag: "1". This tells Vim that the

middle part has an offset of one space.

The middle part "mb:*" starts with "m", which indicates it is a middle

part. The "b" flag means that a blank must follow the text. Otherwise Vim

would consider text like "*pointer" also to be the middle of a comment.

The end part "ex:*/" has the "e" for identification. The "x" flag has a

special meaning. It means that after Vim automatically inserted a star,

typing / will remove the extra space.

For more details see format-comments.

==============================================================================

Next chapter: usr_31.txt Exploiting the GUI