Formatting Code

Inevitably, whoever you are writing code for will dictate how you format code. Sometimes it makes sense, for example, if you use some form of preprocessing to extract code and definitions to create documentation for the code. In many cases, the style that is imposed on you is the personal preference of someone else.

There are two broad styles in C++: K&R and Allman.

Kernighan and Ritchie (K&R) wrote the first, and most influential book about C (Dennis Ritchie was the author of the C language). The K&R style is used to describe the formatting style used in that book. In general, K&R places the opening brace of a code block on the same line of the last statement. If your code has nested statements (and typically, it will) then this style can get a bit confusing:

    if (/* some test */) { 
        // the test is true  
        if (/* some other test */) { 
            // second test is true  
        } else { 
            // second test is false    
        } 
    } else { 
        // the test is false  
    }

This style is typically used in Unix (and Unix-like) code.

The Allman style (named after the developer Eric Allman) places the opening brace on a new line, so the nested example looks as follows:

        if (/* some test */)  
        { 
            // the test is true  
            if (/* some other test */)  
            { 
                // second test is true   
            }  
            else  
            { 
                // second test is false     
            } 
        }  
        else  
        { 
           // the test is false  
        }

The Allman style is typically used by Microsoft.

Remember that your code is unlikely to be presented on paper, so the fact that K&R is more compact will save no trees. If you have the choice, you should choose the style that is the most readable; the decision of this author, for this book, is that Allman is more readable.

If you have multiple nested blocks, the indents can give you an idea of which block the code resides in. However, comments can help. In particular, if a code block has a large amount of code, it is often helpful to comment the reason for the code block. For example, in an if statement, it is helpful to put the result of the test in the code block so you know what the variable values are in that block. It is also useful to put a comment on the closing brace of the test:

    if (x < 0)  
    { 
       // x < 0 
       /* lots of code */ 
    }  // if (x < 0) 

    else  
    { 
       // x >= 0 
       /* lots of code */ 
    }  // if (x < 0)

If you put the test as a comment on a closing brace, it means that you have a search term that you can use to find the test that resulted in the code block. The preceding lines make this commenting redundant, but when you have code blocks with many tens of lines of code, and with many levels of nesting, comments like this can be very helpful.