STRUCTS in C#

Draw Data Matrix ECC200 in C# STRUCTS

As with all value types, a variable of a struct type contains its own data. Consequently A variable of a struct type cannot be null. Two structs variables cannot refer to the same object. For example, the following code declares a class called CSimple, and a struct called Simple, and a variable of each. Figure 12-1 shows how the two would be arranged in memory. class CSimple { public int X; public int Y; } struct Simple { public int X; public int Y; } class Program { static void Main() { CSimple cs = new CSimple(); Simple ss = new Simple(); ...

Assigning one struct to another copies the values from one to the other. This is quite different from copying from a class variable, where only the reference is copied. Figure 12-2 shows the difference between the assignment of a class variable and a struct variable. Notice that after the class assignment, cs2 is pointing at the same object in the heap as cs1. But after the struct assignment, the values of ss2 s members are the same as those of ss1. class CSimple { public int X; public int Y; } struct Simple { public int X; public int Y; } class Program { static void Main() { CSimple cs1 = new CSimple(), cs2 = null; Simple ss1 = new Simple(), ss2 = new Simple(); cs1.X = ss1.X = 5; cs1.Y = ss1.Y = 10; cs2 = cs1; ss2 = ss1; } }

// Assign 5 to ss1.X and cs1.X // Assign 10 to ss1.Y and cs1.Y // Assign class instance // Assign struct instance

The language implicitly supplies a parameterless constructor for every struct. This constructor sets each of the struct s members to the default value for that type. Value members are set to their default values. Reference members are set to null. The predefined parameterless constructor exists for every struct and you cannot delete or redefine it. You can, however, create additional constructors, as long as they have parameters. Notice that this is different from classes. For classes, the compiler will only supply an implicit parameterless constructor if no other constructors are declared. To call a constructor, including the implicit parameterless constructor, use the new operator. Notice that the new operator is used even though the memory is not allocated from the heap. For example, the following code declares a simple struct with a constructor that takes two int parameters. Main creates two instances of the struct one using the implicit parameterless constructor, and the second with the declared two-parameter constructor. struct Simple { public int X; public int Y; public Simple(int a, int b) { X = a; Y = b; } } class Program { static void Main() { Call implicit constructor Simple s1 = new Simple(); Simple s2 = new Simple(5, 10); Call constructor Console.WriteLine("{0},{1}", s1.X, s1.Y); Console.WriteLine("{0},{1}", s2.X, s2.Y); } } // Constructor with parameters

You can also create an instance of a struct without using the new operator. If you do this, however, there are some restrictions, which are the following: You cannot use the value of a data member until you have explicitly set it. You cannot call any function member until all the data members have been assigned. For example, the following code shows two instances of struct Simple created without using the new operator. When there is an attempt to access s1 without explicitly setting the data member values, the compiler produces an error message. There are no problems reading from s2 after assigning values to its members. struct Simple { public int X; public int Y; } class Program { static void Main() { No constructor calls Simple s1, s2; Console.WriteLine("{0},{1}", s1.X, s1.Y); s2.X = 5; Not yet assigned s2.Y = 10; Console.WriteLine("{0},{1}", s2.X, s2.Y); } }