Why is trailing whitespace a big deal? [closed]

Question

Trailing whitespace is enough of a problem for programmers that editors like Emacs have special functions that highlight it or get rid of it automatically, and many coding standards require you to eliminate all instances of it. I'm not entirely sure why though. I can think of one practical reason of avoiding unnecessary whitespace, and it is that if people are not careful about avoiding it, then they might change it in between commits, and then we get diffs polluted with seemingly unchanged lines, just because someone removed or added a space.

This already sounds like a pretty good reason to avoid it, but I do want to see if there's more to it than that. So, why is trailing whitespace such a big deal?

Answer 1

Reasons that it's important to me:

• When I hit the "End" key, I expect the cursor to go to the end of the line (depending what editor I'm using and how it's configured) and I expect to be able to start typing right away. If the cursor gets there and I have to delete 3 or 4 characters, it's annoying. Especially if it's inconsistent throughout the file(s).

• When I have string literals that span multiple lines, trailing whitespace can make the output string look incorrect when it's used.

While not strictly programming, whitespace can seriously mess up data entry, if there's trailing/leading in a file that will be parsed and used as input to something else. This happens the most when a clean, generated input file gets dirtied by someone editing it in Excel or something and then trailing whitespace (and other formatting issueS) can creep in.

Answer 2

I really hate trailing whitespace, but the exact reason is a bit vague.

I guess the origin of that feeling is not in programming, but in the desktop publishing field. Have you ever got a document typed by someone else that needed to be typeset into a publication? In all modern publications, especially when using columns, it is custom to have sentences follow each other sequentially within one paragraph, not starting a new line for each sentence. Well, when there is trailing whitespace, it takes a lot more effort to get it right (lots of search and replace actions that eliminate double spaces, etc...).

Other reasons (in programming), not good reasons, I know, but they bother my subconscious psyche in such aggravating intense manner that they compel me to eliminate it:

• It takes more storage space than necessary
• The parser will have to skip an extra character for no good reason when compiling
• Some editors might add an extra blank line when WordWrap is on and the trailing space doesn't fit

Yes, yes I know! I know, these are junk reasons. I'm not a perfectionist, but... well maybe I am?

The last reason I can think of is inconsistent cursor movement. It feels like the cursor is hanging in thin air at the end of a line, every step to the right may cause it to either drop or to hover further to an unknown extent, it just feels unsteady (like those invisible or disappearing blocks that Super Mario used to jump on).

Probably I can be diagnosed with trailspacefobia?

Answer 3

A lot of these answers almost touch on the reason it's bad for me, but basically: It "breaks" text editors. My experience is with vim.

Vim is designed so that common actions map to letters so cleanly that you don't even have to think about what letter or key combination to hit. Various hotkeys allow the cursor to jump around the text so quickly that it takes only a couple keystrokes to get it to wherever you want. Even things like folding blocks of code is fast, since you can hit END or $ to jump to the end of the line, where the cursor should overlap { or } or ( or ) or something - there's no need to break your thought flow to get an idea onto the screen.

But then comes along some trailing whitespace, and the cursor's movements are no longer predictable. Your typing process is being interrupted because something you can't see is affecting where the cursor goes, so you have to break your train of thought to send it where it should be.

Ever notice how annoyed people get when they're really focused on a task and someone interrupts them? Yeah, finding trailing whitespace when it's least expected is exactly like that.

_{As a sidenote, I've also noticed that people who don't care about trailing whitespace are the ones who use the mouse for navigation, and tend to be slower typists because of it...}

Answer 4

Surprisingly, the most obvious answer is missing: trailing whitespace can and will produce difficult to find bugs.

The most obvious situation is multiline strings. Python, JavaScript and Bash are few examples of the languages which can be affected by this:

print("Hello\·
····World")

produces:

  File "demo.py", line 1
    print("Hello\
                 ^
SyntaxError: EOL while scanning string literal

which is somehow cryptic and difficult to solve if the editor is not configured to display whitespace characters.

While syntax highlight can help avoiding such cases, it's even easier to not having the issue in the first place by not letting whitespace at the end of the lines. This is why some style checkers will raise a warning when encountering trailing whitespace, and some editors will trim them automatically.

^{Illustration: syntax highlight can help avoiding trailing whitespace in situations where it can lead to bugs, but don't rely just on it.}

Another context, briefly mentioned in a previous answer, is data stored in files.

For instance, CSV files which contain trailing whitespace may cause data inconsistency which is also very difficult to detect: standards-compliant parsers will trim the whitespace (the standard indicates that leading or trailing whitespace is irrelevant, unless delimited with double-quotes), but some parsers may misbehave and keep the whitespace as a part of a value.

Other custom formats may specifically consider that whitespace is the part of the value, leading to consistent but still difficult to debug situations.

Answer 5

I recently spent a day looking for a bug that turned out to be an unexpected trailing whitespace in data.

Answer 6

Besides the obvious problem that it breaks parsing in certain cases? As another poster has noted it can cause subtle and difficult to trace errors. Whitespace is not always insignificant. In some cases, trailing whitespace can significantly change the meaning of a line of code or data.

In most cases whitespace is there to format the code for human readers. Trailing whitespace may indicate several things including:

• An incomplete statement;
• A missing comment;
• A mistaken edit; or
• Sloppy editing.

Two of these may result in incorrect funtioning, and another may make it more difficult to comprehend the code.

Answer 7

When I select program source code in order to copy and paste it (or delete it) I find it a bit annoying to see all the irregular extra white space at the end of lines: since I have to read the code while I am selecting it, the trailing white space is an unneeded noise. Example (dots represent the white space):

if (fp)........
{....
    fclose(fp);.
}
else
{.....
    prinft("File is NULL\n");
}..

This example is artificial, but I have seen a lot of code that looks like this.

Answer 8

There are programming languages that are sensitive to end-line whitespace. For example, a TCL script will give an error if there is a whitespace at the end of a line.