c# make barcode Figure 4 1 : Requirements section showing namespace and assembly information for a type in .NET

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Figure 4 1 : Requirements section showing namespace and assembly information for a type
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5: Primitive, Reference, and Value Types
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In this chapter, I ll discuss the different kinds of types that you ll run into as a Microsoft .NET Framework developer. It is crucial that all developers be familiar with the different behaviors that these types exhibit. When I was first learning the .NET Framework, I didn t fully understand the difference between primitive, reference, and value types. This lack of clarity led me to unwittingly introduce subtle bugs and performance issues into my code. By explaining the differences between the types here, I m hoping to save you some of the headaches I experienced while getting up to speed.
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Programming Language Primitive Types
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Certain data types are so commonly used that many compilers allow code to manipulate them using simplified syntax. For example, you could allocate an integer using the following syntax:
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System.Int32 a = new System.Int32();
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But I m sure you d agree that declaring and initializing an integer using this syntax is rather cumbersome. Fortunately, many compilers (including C#) allow you to use syntax similar to the following instead:
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int a = 0;
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This syntax certainly makes the code more readable, and, of course, the intermediate language (IL) generated is identical no matter which syntax is used. Any data types the compiler directly supports are called primitive types. Primitive types map directly to types existing in the .NET Framework Class Library (FCL). For example, in C#, an int maps directly to the System.Int32 type. Because of this, the following four lines of code all compile correctly and produce the exact same IL:
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int System.Int32 int System.Int32 a a a a = = = = 0; 0; new int(); new System.Int32(); // // // // Most convenient syntax Convenient syntax Inconvenient syntax Inconvenient syntax
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Table 5 1 shows the FCL types that have corresponding primitives in C#. For the types that are compliant with the Common Language Specification (CLS), other languages will offer similar primitive types. However, languages aren t required to offer any support for the non CLS compliant types. Table 5 1: FCL Types with Corresponding C# Primitives C# Primitive Type sbyte byte short ushort int uint long ulong FCL Type System.SByte System.Byte System.Int16 System.UInt16 System.Int32 System.UInt32 System.Int64 System.UInt64 109 CLS Compliant Description No Signed 8 bit value Yes Unsigned 8 bit value Yes Signed 16 bit value No Unsigned 16 bit value Yes Signed 32 bit value No Unsigned 32 bit value Yes Signed 64 bit value No Unsigned 64 bit value
char
System.Char
float double bool decimal
System.Single System.Double System.Boolean System.Decimal
Yes Yes Yes Yes
object string
System.Object System.String
Yes Yes
16 bit Unicode character (char never represents an 8 bit value as it would in unmanaged C++.) IEEE 32 bit float IEEE 64 bit float A True/False value A 128 bit high precision floating point value commonly used for financial calculations where rounding errors can t be tolerated. Of the 128 bits, 1 bit represents the sign of the value, 96 bits represent the value itself, and 8 bits represent the power of 10 to divide the 96 bit value by (can be anywhere from 0 to 28). The remaining bits are unused. Base type of all types An array of characters
The C# language specification states, As a matter of style, use of the keyword is favored over use of the complete system type name. I disagree with the language specification; I prefer to use the FCL type names and completely avoid the primitive type names. In fact, I wish that compilers didn t even offer the primitive type names and forced developers to use the FCL type names instead. Here are my reasons: I ve seen a number of developers confused, not knowing whether to use string or String in their code. Because, in C#, the string (a keyword) maps exactly to System.String (a FCL type), there is no difference and either can be used. In C#, long maps to System.Int64, but in a different programming language, long could map to an Int16 or Int32. In fact, C++ with Managed Extensions does in fact treat long as an Int64. Someone reading source code in one language could easily misinterpret the code s intention if they were used to programming in a different programming language. In fact, most languages won t even treat long as a keyword and won t compile code that uses it. The FCL has many types with methods that have type names in the method. For example, the BinaryReader type offers methods such as ReadBoolean, ReadInt32, ReadSingle, and so on, and the System.Convert type offers methods such as ToBoolean, ToInt32, ToSingle, and so on. Although it s legal to write the following code, the line with float feels very unnatural to me, and it s not obvious that the line is correct:
BinaryReader br = new BinaryRead(...); float val = br.ReadSingle(); // OK, but feels unnatural Single val = br.ReadSingle(); // OK and feels good
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