The Facts Behind the Code Indention Style War

About a week ago an anonymous visitor to Experiment Garden made the following comment:

"Please, please, PLEASE, for humanity's sake: use the Kernighan and Ritchie's indenting style!
Don't use braces for single line statements.
Much less, put them in their own lines!

Vertical space is precious. By committing those sins, you're making your code unnecessaringly [sic] long, which means I must scroll down to read it completely, whereas it could've fitted in very few lines, if you take out all the fluff!!!"

This is just one more example of the great code indention style war that has plagued programmers for decades.

In most languages code indention isn't a requirement. Compilers leave a great deal of room for flexibility in how code is formatted. As long as you use braces and semicolons to separate blocks and statements the compiler will process the code. Code indention is purely for the convenience of programmers and others who need to read and debug code. Indention is designed to help blocks and logic levels to stand out.


The Allman Brace Style

Personally, I favor the Allman Brace style, which is credited to Eric Allman, the programmer who created sendmail. In the Allman style code brace blocks are placed one line below their respective control structures, at the same indentation level. The code inside the braces is indented one level.

if(condition_variable==condition1)
{
  //Some code.
  condition_variable=condition2;
}
else if(condition_variable==condition2)
{
  //Some code.
  condition_variable=condition1;
}
else
{
  //Some code
  condition_variable=false;
}

In my opinion, the Allman brace style is easier to read because it separates the code into solid blocks that can quickly be distinguished from the rest of the code. The conditional control structures associated with each block are one line above.

One major advantage to Allman is that it allows you to comment out entire blocks of code with very little work. In addition you can have multiple control statements for testing purposes and easily comment out one to try another. For example:

if(condition_variable==condition1)
/*if(condition_variable==condition2)*/
{
  //Alternate control structures being tried.
  condition_variable=condition2;
}


if(condition_variable==condition2)
/*{
  //Block temporarily commented out.
  condition_variable=condition1;
}*/

According to some sources the Allman brace style is most popular with C++ and C# programmers.

The Kernigan and Richie Brace Style

The Kernigan and Richie style, typically abbreviated to K&R style, is clearly the indentation style of choice for my anonymous commenter. The Kernigan and Richie style was introduced in the popular book "The C Programming Language" by Kernigan and Richie.

The difference between K&R style and Allman style is that K&R style places the opening brace on the same line as the control statement.

if(condition_variable==condition1) {
  //Some code.
  condition_variable=condition2;
} else if(condition_variable==condition2) {
   //Some code.
   condition_variable=condition1;
} else {
  //Some code
  condition_variable=false;
}

In my personal opinion, K&R style is considerably harder to read, because there is no vertical space between the code in the block and the control structures associated with it. The code tends to run together, making it harder to locate the start and end of code blocks.

According to my anonymous commenter, however, "vertical space is precious" and the extra "fluff" forces the person reading the code to scroll down to read it. Interestingly the K&R style was especially popular in the early days of C programming because computer terminals had limited resolution, and vertical space was very precious.

These days high definition monitors are common, with the typical resolution being 1024x768. In most cases vertical space is no longer a problem. However, there are still people who like the K&R style, probably because they began programming back when K&R was the dominant coding style.

Many books that teach beginning programming also make use of K&R style. This is because in a book vertical space is still precious. There is a limited amount of vertical space on each page, and if the Allman style was used extra pages would have to be added to make room for all the extra lines.

In a real world program, though, or a blog or website vertical space is not so precious. You can always scroll down in the browser or IDE to see more code.

The War Behind Indentation Style

As I did research for this post and examined blog posts and forum discussions across the web it became clear to me that there is no solid agreement on any one indentation style in particular. This leads to interesting dilemmas, especially in the work environment.

In his article "Search for the One True Indentation Style" Sai Matam describes what happened when two software project managers both wanted to review his code daily. The only problem was that one expected the code to be in K&R style, while the other demanded that he use Allman style. Sai Matam's solution was to write two copies of the code, one in K&R style, the other in Allman style. The extra time involved in syncing the two copies must have been immense.

Further complicating the indentation war is the continued conflict between those who indent their code using spaces and those who indent using tabs. For example, the EmacsWiki goes into great detail to explain why tabs are evil. Meanwhile article writer Xah Lee makes his argument to explain why tabs are proper, and spaces are improper.

Personally I prefer spaces over tabs because tabs can vary from system to system and IDE to IDE. One person may configure tabs to be the equivalent of four spaces, whereas I have tabs set up to be two spaces. This changes code alignment, especially if you use formatting to line up variable assignments. Suddenly what was once a very readable technique for assigning values to a group of variable becomes an unreadable mess.

However, others make the argument that tabs are specifically designed for formatting while spaces are like a work around. According to Xah Lee, in his article mentioned above, tabs are proper because they give formatting options. If someone doesn't like the way the code looks they can just change the tab space settings and all indention over the whole code base will be adjusted. This would be considerably more difficult to do if spaces were used rather than tabs.

Conclusion

There are obviously advantages and disadvantages to each style preference. Personally I like Allman's style with spaces for indentation. These days, though, any decent IDE can reformat all your code for you. If someone viewing it doesn't like Allman, all they have to do is refactor the code in K&R.

If IDE's were really intelligent they could be configured to auto format all code that enters the IDE. Then programmers would only have to set their preferred coding style preference once, and from then on they would see all code in that style. If HTML code tags had a language attribute and more complicated functionality then browsers could also be made to reformat code automatically. In time the war between advocates of Allman's style and K&R could become a thing of the past, with each side viewing code in their preferred style, blissfully unaffected by users of the "wrong" coding style.

Maybe it will happen in the future. In the meantime, I'll just walk the middle path. On this blog I will use Allman's in some articles, and K&R in others. It will all depend on how long the code samples are and how I want them to fit in the vertical space.

What is your favorite code indention style and why do you use it over other styles?