C Programming Guidelines

C# Programming Guidelines

This final section of this chapter looks at the guidelines you need to bear in mind when writing C# programs.

Rules for Identifiers

This section examines the rules governing what names you can use for variables, classes, methods, and so on. Note that the rules presented in this section are not merely guidelines: They are enforced by the C# compiler.

Identifiers are the names you give to variables, to user-defined types such as classes and structs, and to members of these types. Identifiers are case-sensitive, so for example variables named interestRate and InterestRate would be recognized as different variables. Following are a couple of rules determining what identifiers you can use in C#:

• They must begin with a letter or underscore, although they can contain numeric characters.

• You can't use C# keywords as identifiers.

C# has the following reserved keywords:

abstract	do	Implicit	params	switch
as	double	In	private	this
base	else	Int	protected	throw
bool	enum	Interface	public	true
break	event	Internal	readonly	try
byte	explicit	Is	ref	typeof
case	extern	lock	return	uint
catch	false	long	sbyte	ulong
char	finally	namespace	sealed	unchecked
checked	fixed	new	short	unsafe
class	float	null	sizeof	ushort
const	for	object	stackalloc	using
continue	foreach	operator	static	virtual
decimal	goto	out	string	volatile
default	if	override	struct	void
delegate				while

If you do need to use one of these words as an identifier (for example, if you are accessing a class written in a different language), you can prefix the identifier with the @ symbol to indicate to the compiler that what follows is to be treated as an identifier, not as a C# keyword (so abstract is not a valid identifier, but @abstract is).

Finally, identifiers can also contain Unicode characters, specified using the syntax \uXXXX, where XXXX is the four-digit hex code for the Unicode character. The following are some examples of valid identifiers:

• Name

• berflu

• _Identifier

• \u005fIdentifier

The last two items in this list are identical and interchangeable (because 005f is the Unicode code for the underscore character), so obviously these identifiers couldn't both be declared in the same scope. Note that although syntactically you are allowed to use the underscore character in identifiers, this isn't recommended in most situations, because it doesn't follow the guidelines for naming variables that Microsoft has written to ensure that developers use the same conventions, making it easier to read each other's code.

Usage Conventions

In any development language, there usually arise certain traditional programming styles. The styles are not part of the language itself but are conventions concerning, for example, how variables are named or how certain classes, methods, or functions are used. If most developers using that language follow the same conventions, it makes it easier for different developers to understand each other's code — which in turn generally helps program maintainability. For example, a common (though not universal) convention in Visual Basic 6 was that variables that represents strings have names beginning with lowercase s or lowercase str, as in the Visual Basic 6 statements Dim sResult As String or Dim strMessage As String. Conventions do, however, depend on the language and the environment. For example, C++ developers programming on the Windows platform have traditionally used the prefixes psz or lpsz to indicate strings — char *pszResult; char *lpszMessage; — but on Unix machines it's more common not to use any such prefixes: char *Result; char *Message;.

You'll notice from the sample code in this book that the convention in C# is to name variables without prefixes: string Result; string Message;.

Note

The convention by which variable names are prefixed with letters that represent the data type is known as Hungarian notation. It means that other developers reading the code can immediately tell from the variable name what data type the variable represents. Hungarian notation is widely regarded as redundant in these days of smart editors and IntelliSense.

Whereas, with many languages, usage conventions simply evolved as the language was used, with C# and the whole of the .NET Framework Microsoft has written very comprehensive usage guidelines, which are detailed in the .NET/C# MSDN documentation. This should mean that, right from the start,.NET programs will have a high degree of interoperability in terms of developers being able to understand code. The guidelines have also been developed with the benefit of some twenty years hindsight in object-oriented programming, and as a result have been carefully thought out and appear to have been well received in the developer community to judge by the relevant newsgroups. Hence the guidelines are well worth following.

It should be noted, however, that the guidelines are not the same as language specifications. You should try to follow the guidelines when you can. Nevertheless, you won't run into problems if you do have a good reason for not doing so — for example, you won't get a compilation error because you don't follow these guidelines. The general rule is that if you don't follow the usage guidelines you must have a convincing reason. Departing from the guidelines should be a positive decision rather than simply not bothering. Also, if you compare the guidelines with the samples in the remainder of this book, you'll notice that in numerous examples in this book, we have chosen not to follow the conventions. That's usually because the conventions are designed for much larger programs than our samples, and although they are great if you are writing a complete software package, they are not really so suitable for small 20-line standalone programs. In many cases, following the conventions would have made our samples harder rather than easier to follow.

The full guidelines for good programming style are quite extensive. This section is confined to describing some of the more important guidelines, as well as the ones most likely to surprise you. If you want to make absolutely certain that your code follows the usage guidelines completely, you will need to refer to the MSDN documentation.

Naming conventions

One important aspect to making your programs understandable is how you choose to name your items — and that includes naming variables, methods, classes, enumerations, and namespaces.

It is intuitively obvious that your names should reflect the purpose of the item and should be designed not to clash with other names. The general philosophy in the .NET Framework is also that the name of a variable should reflect the purpose of that variable instance and not the data type. For example, height is a good name for a variable, whereas integerValue isn't. However, you will probably feel that that principle is an ideal that is hard to achieve. Particularly when you are dealing with controls, in most cases, you'll probably feel happier sticking with variable names like confirmationDialog and chooseEmployeeListBox, which do indicate the data type in the name.

The following sections look at some of the things you need to think about when choosing names.

Casing of names

In many cases you should use Pascal casing for names. Pascal casing means that the first letter of each word in a name is capitalized: EmployeeSalary, ConfirmationDialog, PlainTextEncoding. You will notice that essentially all of the names of namespaces, classes, and members in the base classes follow Pascal casing. In particular, the convention of joining words using the underscore character is discouraged. So you should try not to use names like employee_salary. It has also been common in other languages to use all capitals for names of constants. This is not advised in C#, because such names are harder to read — the convention is to use Pascal casing throughout:

 const int MaximumLength; 

The only other casing scheme that you are advised to use is camel casing. Camel casing is similar to Pascal casing, except that the first letter of the first word in the name is not capitalized: employeeSalary, confirmationDialog, plainTextEncoding. Following are three situations in which you are advised to use camel casing:

• For names of all private member fields in types:

   public int subscriberID; 

  Note, however, that often it is conventional to prefix names of member fields with an underscore:

   public int subscriberID; 

• For names of all parameters passed to methods:

   public void RecordSale(string salesmanName, int quantity); 

• To distinguish items that would otherwise have the same name. A common example is when a property wraps around a field:

   private string employeeName; public string EmployeeName { get { return employeeName; } } 

If you are doing this, you should always use camel casing for the private member and Pascal casing for the public or protected member, so that other classes that use your code see only names in Pascal case(except for parameter names).

You should also be wary about case-sensitivity. C# is case-sensitive, so it is syntactically correct for names in C# to differ only by the case, as in the previous examples. However, you should bear in mind that your assemblies might at some point be called from Visual Basic .NET applications — and Visual Basic .NET is not case-sensitive. Hence, if you do use names that differ only by case, it is important to do so only in situations in which both names will never be seen outside your assembly. (The previous example qualifies as okay because camel case is used with the name that is attached to a private variable.) Otherwise you may prevent other code written in Visual Basic .NET from being able to use your assembly correctly.

Name styles

You should try to be consistent about your style of names. For example, if one of the methods in a class is called ShowConfirmationDialog(), then you should not give another method a name like Show DialogWarning(), or WarningDialogShow(). The other method should be called ShowWarning Dialog(). Get the idea?

Namespace names

Namespace names are particularly important to design carefully in order to avoid risk of ending up with the same name for one of your namespaces as someone else uses. Remember, namespace names are the only way that .NET distinguishes names of objects in shared assemblies. So if you use the same name- space name for your software package as another package, and both packages get installed on the same computer, there are going to be problems. Because of this, it's almost always a good idea to create a top- level namespace with the name of your company, and then nest successive namespaces that narrow down the technology, group, or department you are working in or the name of the package your classes are intended for. Microsoft recommends namespace names that begin with<CompanyName>.<TechnologyName> as in these two examples:

WeaponsOfDestructionCorp.RayGunControllers  WeaponsOfDestructionCorp.Viruses 

Names and keywords

It is important that the names do not clash with any keywords. In fact, if you attempt to name an item in your code with a word that happens to be a C# keyword, you'll almost certainly get a syntax error because the compiler will assume the name refers to a statement. However, because of the possibility that your classes will be accessed by code written in other languages, it is important that you also don't use names that are keywords in other .NET languages. Generally speaking, C++ keywords are similar to C# keywords, so confusion with C++ is unlikely, and those commonly encountered keywords that are unique to Visual C++ tend to start with two underscore characters. Like C#, C++ keywords are spelled in lowercase, so if you hold to the convention of naming your public classes and members with Pascal-style names, they will always have at least one uppercase letter in their names, and there will be no risk of clashes with C++ keywords. On the other hand, you are more likely to have problems with Visual Basic.NET, which has many more keywords than C# does, and being non–case-sensitive means you cannot rely on Pascal-style names for your classes and methods.

The following table lists the keywords and standard function calls in Visual Basic .NET, which should if possible be avoided, in whatever case combination, for your public C# classes:

Abs	Do	Loc	RGB
Add	Double	Local	Right
AddHandler	Each	Lock	RmDir
AddressOf	Else	LOF	Rnd
Alias	ElseIf	Log	RTrim
And	Empty	Long	SaveSettings
Ansi	End	Loop	Second
AppActivate	Enum	LTrim	Seek
Append	EOF	Me	Select
As	Erase	Mid	SetAttr
Asc	Err	Minute	SetException
Assembly	Error	MIRR	Shared
Atan	Event	MkDir	Shell
Auto	Exit	Module	Short
Beep	Exp	Month	Sign
Binary	Explicit	MustInherit	Sin
BitAnd	ExternalSource	MustOverride	Single
BitNot	False	MyBase	SLN
BitOr	FileAttr	MyClass	Space
BitXor	FileCopy	Namespace	Spc
Boolean	FileDateTime	New	Split
ByRef	FileLen	Next	Sqrt
Byte	Filter	Not	Static
ByVal	Finally	Nothing	Step
Call	Fix	NotInheritable	Stop
Case	For	NotOverridable	Str
Catch	Format	Now	StrComp
CBool	FreeFile	NPer	StrConv
CByte	Friend	NPV	Strict
CDate	Function	Null	String
CDbl	FV	Object	Structure
CDec	Get	Oct	Sub
ChDir	GetAllSettings	Off	Switch
ChDrive	GetAttr	On	SYD
Choose	GetException	Open	SyncLock
Chr	GetObject	Option	Tab
CInt	GetSetting	Optional	Tan
Class	GetType	Or	Text
Clear	GoTo	Overloads	Then
CLng	Handles	Overridable	Throw
Close	Hex	Overrides	TimeOfDay
Collection	Hour	ParamArray	Timer
Command	If	Pmt	TimeSerial
Compare	Iif	PPmt	TimeValue
Const	Implements	Preserve	To
Cos	Imports	Print	Today
CreateObject	In	Private	Trim
CShort	Inherits	Property	Try
CSng	Input	Public	TypeName
CStr	InStr	Put	TypeOf
CurDir	Int	PV	UBound
Date	Integer	QBColor	UCase
DateAdd	Interface	Raise	Unicode
DateDiff	Ipmt	RaiseEvent	Unlock
DatePart	IRR	Randomize	Until
DateSerial	Is	Rate	Val
DateValue	IsArray	Read	Weekday
Day	IsDate	ReadOnly	While
DDB	IsDbNull	ReDim	Width
Decimal	IsNumeric	Remove	With
Declare	Item	RemoveHandler	WithEvents
Default	Kill	Rename	Write
Delegate	Lcase	Replace	WriteOnly
DeleteSetting	Left	Reset	Xor
Dim	Lib	Resume	Year
Dir	Line	Return

Use of properties and methods

One area that can cause confusion in a class is whether a particular quantity should be represented by a property or a method. The rules here are not hard and fast, but in general, you ought to use a property if something really should look and feel like a variable. (If you're not sure what a property is, see Chapter 3, "Objects and Types.") This means, among other things, that:

• Client code should be able to read its value. Write-only properties are not recommended, so for example use a SetPassword() method, not a write-only Password property.

• Reading the value should not take too long. The fact that something is a property usually suggests that reading it will be relatively quick.

• Reading the value should not have any observable and unexpected side effect. Further, setting the value of a property should not have any side effect that is not directly related to the property. Setting the width of a dialog box has the obvious effect of changing the appearance of the dialog box on the screen. That's fine, as that's obviously related to the property in question.

• It should be possible to set properties in any order. In particular, it is not good practice when setting a property to throw an exception because another related property has not yet been set. For example, if in order to use a class that accesses a database you need to set ConnectionString, UserName, and Password, then the author of the class should make sure the class is implemented so the user really can set them in any order.

• Successive reads of a property should give the same result. If the value of a property is likely to change unpredictably, you should code it up as a method instead. Speed, in a class that monitors the motion of an automobile, is not a good candidate for a property. Use a GetSpeed() method here; on the other hand, Weight and EngineSize are good candidates for properties because they will not change for a given object.

If the item you are coding satisfies all of the preceding criteria, it is probably a good candidate for a property. Otherwise you should use a method.

Use of fields

The guidelines are pretty simple here. Fields should almost always be private, except that in some cases it may be acceptable for constant or read-only fields to be public. The reason is that if you make a field public, you may hinder your ability to extend or modify the class in the future.

The previous guidelines should give you a rough idea of good practices, and you should also use them in conjunction with good object-oriented programming style.

It's also worth bearing in mind that Microsoft has been fairly careful about being consistent and has followed its own guidelines when writing the .NET base classes. So a very good way to get an intuitive feel for the conventions to follow when writing .NET code is to simply look at the base classes — see how classes, members, and namespaces are named, and how the class hierarchy works. If you try to write your code in the same style as the base classes, you shouldn't go wrong.