Musings on the Formatting of C and C++ Code

Ben Key: Ben.Key@YekNeb.com

October 4, 2013; October 26, 2018

 

I was watching the video The Care and Feeding of C++’s Dragons. I found it to be very interesting. I especially found the CLang based program that reformats code to be promising. However, there were some things about the tool that I find disturbing. It seems to use some formatting patterns that I think are huge mistakes.

To illustrate, some of the sample code looks like the following.

int functionName(int a, int b, int c,
                 int d, int e, int f,
                 int g, int h, int i) const {
  /* Code omitted. */
  if (test()) {
    /* Code omitted. */
  }
}

There are two problems that I see with formatting code in this way. The first is that on the line where the list of variables is continued, there is a great deal of what I see as entirely unnecessary white space. In my opinion it should be as follows.

int functionName(int a, int b, int c,
  int d, int e, int f,
  int g, int h, int i) const {

Or, my personal preference would be the following.

int functionName(
  int a, int b, int c,
  int d, int e, int f,
  int g, int h, int i) const {

My reasoning is quite simple.

Examine what happens when the name of the function is changed to something longer, as follows, and then it is reformated. The code becomes as follows.

int aMuchLongerFunctionName(int a, int b, int c
                            int d, int e, int f,
                            int g, int h, int i) const {

If you do a diff of the original version of the code and the new code, it will show that three lines have changed instead of showing that only one line has changed. I am aware of the fact that many diff tools have an ignore white space option and that if this option is set it will only show one line as having changed. However, not all diff tools have that option. In addition, some companies and organizations have a strict policy that every line of code that changes must be changed for a purpose associated with a given task. And these companies do not accept changes that are only related to reformatting as being associated with a given task. In essence, if the changed line does not affect the functionality of the code, it is not an acceptable change. And these organizations will deliberately not turn on the ignore white space option and will turn a deaf ear to the argument that they should just enable that option (can you tell that I am speaking from experience?).

If you are in such a situation and you change the name of a function that initially is formatted with the parameter list aligned with the end of the function name and you adhere to a strict “every changed line must have a functional purpose” rule you will inevitably end up with the following.

int aMuchLongerFunctionName(int a, int b, int c
                 int d, int e, int f,
                 int g, int h, int i) const {

This just looks wrong!

There is also another reason for not aligning the parameters with the end of the function name. Consider the following.

int aVeryLongFunctionNameThatGoesBeyondTheEdgeOfTheScreen(int a, int b, int c,
                                                          int d, int e, int f,
                                                          int g, int h, int i) const {

In this case, you cannot see the parameters at all without wasting your time scrolling across the screen.

If you always begin the parameter list on its own line that is indented one level deep as follows, you would not ever have to scroll the screen just to see the parameter list.

int aVeryLongFunctionNameThatGoesBeyondTheEdgeOfTheScreen(
  int a, int b, int c,
  int d, int e, int f,
  int g, int h, int i) const {

The second issue I have is with putting braces at the end of the line. In C and C++ braces are optional for some statements such as if. And lets face the facts, C and C++ is often inconsistently indented. Putting braces at the end leads to more work in the following scenario.

if (aVeryLongTestThatGoesPastTheEdgeOfTheScreen()) {
  /*
       Thousands
 of
         inconsistently indented
    lines of
 code /*
}

Putting the brace at the end of the if line forces someone who is reading the code to hit the end key to determine how much code will only be called if the condition is true, one line or thousands of lines, when they might not give a damned about seeing the end of the test because the beginning of it is enough to tell them whether or not the condition can be true in the scenario they are working on. What if the person knows that in the case they are working on, the function “aVeryLongTestThatGoesPastTheEdgeOfTheScreen” will return false. They really do not need to see the end of the test in this case except to find out how many lines they need to skip past in order to get to code that is relevant to their task. Why not just put the brace on a line by itself and make everyone’s life so much easier? Why force someone to hit the end key just so they can answer the following question. How many lines do I need to skip to get to code that is relevant to my task?

Until C and C++ do as they did in the Go language and make the braces mandatory, I believe braces should never be at the end of the line.

In Go, where the braces are mandatory, it does not matter as much to me because I know that if the code compiles the brace is there and I do not care if I cannot see it. But in C and C++, I do not want you to force me to find and hit the end key just so I can tell where your if statement ends. Of course, that does not mean that I think that the decision to put the brace at the end was a good one for Go. I often use a paren matching feature to skip past the irrelevant code in the scenario I have described. That requires that the caret be on the opening paren. In Go I need to hit the end key anyway just to get the caret on the brace so I can use the paren matching feature to skip past code I do not care about. Why? If the brace were on a line by itself, I do not need to locate and hit the end key. I can just arrow down to the brace line and use the paren matching feature.

I know that these arguments are only relevant to the placement of braces for conditional statements and that they are not relevant to the placement of braces at the beginning of functions. However, I still feel that the opening brace of a function should be on a line by itself for the sake of consistency.

I cannot believe other people have adopted code formatting patterns that to me are so obviously mistakes. Is there something I am missing that makes my arguments invalid?

And before you say, “just hit the end key, it is not that hard,” consider the fact that some people are hunt an peck typists. For some people, any extra key they need to hunt for unnecessarily is an aggravation that interrupts their work flow. I am certain that for some people who are touch typists, hitting one additional key is no big deal, but for hunt and peck typists, it can be.

I for one am a hunt and peck typist despite the fact that I began using computers in 1985 and for me finding the end key just to find out how many lines of code will only get called in the condition is true case is enough of a disruption that I find it to be extremely annoying.

When I first wrote this article back in 2013, I was not aware of the many options for customizing the behavior of clang-format.

Fortunately, you can easily customize the behavior of clang-format. There are numerous Clang-Format Style Options available. For example, you can instruct clang-format to “always break after an open bracket, if the parameters don’t fit on a single line” by setting AlignAfterOpenBracket to AlwaysBreak.

When you use clang-format to format a file it will search for a “.clang-format file located in one of the parent directories of the source file” and load the various formatting options from there. Clang-format also has a number of predefined coding styles to choose from: LLVM, Google, Chromium, Mozilla, and WebKit. You can use the -fallback-style and -style command line arguments to specify the coding style you wish to use. For more information see the ClangFormat manual.

I have begun using clang-format for my own open source projects, and I am pleased with the results. If you are interested, you can take a look at my SnKOpen .clang-format file.

There are various websites that will help you to generate the perfect .clang-format file for your project. One of the best is the clang-format configurator. The Unformat project, which generates a .clang-format file from example codebase may also be worth investigating.

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To Brace Or Not To Brace

Summary

In this article I discuss my opinions on when braces should be used to delineate blocks of code in C and C++. In addition I discuss my views on where in the code the braces should be placed. I use examples from thirteen years of experience in C and C++ programming to back up my opinions.

Discussion

One commonly debated topic in C and C++ programming is whether or not braces should be used with if, while, and for statements in C and C++. The debate stems from the fact that if the if, while, or for statement requires exactly one statement after the test, braces are not required. For example, the following is allowed in the C and C++ language specifications:

if ({test})
    {statement}

while ({test})
    {statement}

for ({start}; {test}; {next})
    {statement}

According to the C and C++ language specifications braces are only considered mandatory if more than one statement is to be executed when the {test} evaluates to true. In fact, the C and C++ language specifications allow {statement} to be on the same line as the {test}.

However, it is my professional opinion that {statement} should never be placed on the same line as the {test}. In addition, braces should be considered mandatory.

First I will discuss the basis for my opinion that {statement} should never be placed on the same line as the {test} in if, for, and while statements.

Consider the following code snippet:

if (foo()) bar();
    baz();

When tracing through this code snippet in a debugger the debugger will stop on the

if (foo()) bar();

line. When the user uses the “step over” command, the debugger stops on the

baz();

line. The debugger gives no indication of whether or not the function bar was ever called.

If this code snippet were written as follows,

if (foo())
    bar();
baz();

the following will happen as the user steps through the code. First, the debugger will stop on the

if (foo())

line. When the user uses the “step over” command, the debugger will stop on the bar line if foo returned true. Otherwise the debugger will stop on the baz line next. By simply changing the formatting so that the call to bar is on its own line the code becomes much easier to debug and the user no longer has any doubt about whether or not the function bar was called. For this reason, the {statement} should never be placed on the same line as the {test} of a if, for, or while statement.

Some will argue that the user can use the step in command to determine if bar is called in the original version of the if statement. However, it is not practical to do so. This is because the first time the step in command is used on the

if (foo()) bar();

line, the debugger will step into foo. The user will then have to use the step out command to return to the function containing the if statement and use the step in command again to determine whether or not bar is called.

Matters are worse if the {test} of the if statement is more complicated such as the following:

if ((foo1() || foo2() || foo3()) && foo4()) bar();

In this case the user will need to use the step in, step out, step in sequence as many as four times just to find out if bar is called. Expecting someone to go to this much trouble to determine if a single function is called is simply unreasonable.

Next I will discuss the basis for my opinion that braces should be considered mandatory.

First, changes over time are easier to track if braces are considered to be mandatory. Consider the following function in which the if statement is written without braces:

/* revision 1 */
void fun()
{
    if (foo())
        bar();
    baz();
}

Every application changes over time. Lets say that the function changes so that the function bar1 needs to be called in addition to the function bar if foo returns true. The function fun becomes as follows:

/* revision 2 */
void fun()
{
    if (foo())
    {
        bar();
        bar1();
    }
    baz();
}

If you use a tool such as diff to determine what the changes between revision 1 and 2 of this function, it will indicate that three lines of code changed. The first change is the addition of the open brace. The second change is the addition of the call to bar1 after the call to bar. The third change is the addition of the closing brace. However, there was only one line of code that changed the actual functionality of the function fun.

If revision 1 of fun were written as follows:

/* revision 1 */
void fun()
{
    if (foo())
    {
        bar();
    }
    baz();
}

then diff would indicate that only one line had changed.

Next considering braces to be mandatory protects you from possible mistakes by developers making changes to your code when they are in a hurry and under a lot of pressure. Consider the original version of the function fun listed above. Lets assume that a developer wished to modify the function so that it would write a message to a log file when fun is about to call bar, but they are in a hurry or perhaps had just finished a task in Python which uses indentation and not braces to delineate code blocks and forget to add the braces. Then the function becomes as follows:

/* revision 2 */
void fun()
{
    if (foo())
        log("fun calling bar because foo returned TRUE.");
        bar();
    baz();
}

This code will compile without warnings. However, it will change the behavior of fun in an obviously unwanted way in that fun is now calling bar even if foo does not return TRUE. Fortunately it is easy to tell that this change in behavior was not intended in this case.

The problem becomes more complicated in situations in which instead of adding code to log the function call, the task is to have a function be called before bar if foo returns TRUE. Again lets assume that the developer is in a hurry or still has Python on his mind so he forgets to add the braces. Then the function fun becomes as follows:

/* revision 2 */
void fun()
{
    if (foo())
        fun1();
        bar();
    baz();
}

This code will also compile without any warnings. However, determining if this change is in error is not as easy as in the first case in which the change was the addition of a line of code intended for logging. By just looking at the code can you tell with 100% certainty that the developer who made this change did not intend to change the function fun so that bar is called all the time without asking the developer who made the change? If you are using a source control tool such as subversion to track changes to your software over time and the developer provides detailed change descriptions it is possible that you could. However, under most circumstances, you could not be 100% certain that the change in behavior was not intentional without talking to the developer who made the change. Then what will you do if the developer had died or is unavailable for some other reason?

If braces are considered mandatory, this problem will never come up in your project.

The final reason that braces should be considered mandatory is that it eases code navigation in modern text editors. Most modern text editors have a brace matching capability that allows you to jump to the matching brace. In if, for, and while statements this lets you jump to the end of the statement with a single command. For simple if, for, and while statements this makes no difference. However, there are cases in which the braces for one statement are optional rule is misused and code is written like this.

if ({test})
    if ({test1})
        if ({test2})
            for ({start}; {test3}; {next})
            {
                /*
                several thousand lines of code
                */
            }

In the case that you are reading through this code and you know that {test} does not return TRUE, you do not care about what happens if {test} returns TRUE. You want to move past the for loop to find out what happens if {test} returns FALSE. If braces were present for the “if ( {test} )” statement, you could simply press down arrow once and then use the move to matching brace command to move on to that section of code. However, there are no braces so you have to arrow down four times before using the move to matching brace command. If this same code were written as follows, the extra three keystrokes would not be necessary.

if ({test})
{
    if ({test1})
    {
        if ({test2})
        {
            for ({start}; {test3}; {next})
            {
                /*
                several thousand lines of code
                */
            }
        }
    }
}

There is also a debate about where the braces should be placed in code. In all my examples the opening brace is located on its own line. However, many programmers prefer to place the opening brace at the end of the if, for, or while line as follows:

if ({test}) {
    {statement}
}

This is perfectly legal according to the C and C++ language specifications. However it is my opinion that this should never be done, that the opening brace should always be placed on its own line. Consider the following:

if ({AVeryLongAndComplicatedTestThatGoesOffTheRightEdgeOfTheScreen}) {
    {statement}
    {statement1}
    /*
    several thousand more lines of code
    */
}

In this case, assuming that the test actually does go off the right edge of the screen, can you tell with absolute certainty that {statement1} and the several thousand additional lines of code will only get called if the test returns TRUE without going to the trouble of using the end key to determine whether or not the if line ends in a brace? Simply depending on indentation is not an accurate indicator. This is because the C and C++ language specification allows for different levels of indentation to be used in the same block of code. For example the following is legal in C and C++.

if ({test})
{
    {statement}
        {statement1}
{statement3}
    {statement4}
}

The fact is that in code where braces are placed at the end of the if, for, or while line, someone reading the code must go through the trouble to using the end key every time a if, for, or while line is encountered that goes off the right edge of the screen in order to determine whether or not multiple lines of code or a single line of code gets called when the test returns TRUE. This simply makes the job of reviewing the code much more difficult.

Too summarize, braces should be considered mandatory in if, for, and while statements in order to make tracking changes over time easier, to protect you from the harried programmer phenomena, and to make navigating through your code easier. In addition, the {statement} should never be placed on the same line as the {test} in if, for, or while statements in order to make it easier to debug your code. Finally, braces should never be placed at the end of the if, for, or while line in order to make it easier to determine whether one statement or many statements get called if the {test} returns TRUE when the test is long enough that it actually goes off the right edge of the screen.