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Санкт-Петербургский государственный электротехнический университет "ЛЭТИ"

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Электротехника

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C-sharp language specification.2004.pdf

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Chapter 8 Language overview

1that unsafe code cannot masquerade as safe code. These restrictions limit the use of unsafe code to situations

2in which the code is trusted.

3The example

4using System;

5class Test

7	static void WriteLocations(byte[] arr) {
8	unsafe {
9	fixed (byte* pArray = arr) {
10	byte* pElem = pArray;
11	for (int i = 0; i < arr.Length; i++) {
12	byte value = *pElem;
13	Console.WriteLine("arr[{0}] at 0x{1:X} is {2}",
14	i, (uint)pElem, value);
15	pElem++;
16	}
17	}
18	}
19	}
20	static void Main() {
21	byte[] arr = new byte[] {1, 2, 3, 4, 5};
22	WriteLocations(arr);

23}

24}

25shows an unsafe block in a method named WriteLocations that fixes an array instance and uses pointer

26manipulation to iterate over the elements. The index, value, and location of each array element are written to

27the console. One possible example of output is:

28arr[0] at 0x8E0360 is 1

29arr[1] at 0x8E0361 is 2

30arr[2] at 0x8E0362 is 3

31arr[3] at 0x8E0363 is 4

32arr[4] at 0x8E0364 is 5

33but, of course, the exact memory locations can be different in different executions of the application.

348.5 Expressions

35C# includes unary operators, binary operators, and one ternary operator. The following table summarizes the

36operators, listing them in order of precedence from highest to lowest:

C# LANGUAGE SPECIFICATION

Subclause	Category	Operators

14.5	Primary	x.y f(x) a[x] x++ x-- new
		typeof		checked			unchecked

14.5.13	Unary	+	-	!	~ ++x		--x	(T)x

14.7	Multiplicative	*	/	%

14.7	Additive	+	-

14.8	Shift	<<	>>

14.9	Relational and	<	>	<=	>=	is	as
	type-testing

14.9	Equality	==	!=

14.10	Logical AND	&

14.10	Logical XOR	^

14.10	Logical OR	\|

14.11	Conditional	&&
	AND

14.11	Conditional OR	\|\|

14.12	Conditional	?:

14.13	Assignment	=	*=	/=	%=	+=	-=	<<= >>= &= ^= \|=

2 When an expression contains multiple operators, the precedence of the operators controls the order in which 3 the individual operators are evaluated. For example, the expression x + y * z is evaluated as

4 x + (y * z) because the * operator has higher precedence than the + operator.

5When an operand occurs between two operators with the same precedence, the associativity of the operators

6controls the order in which the operations are performed:

7• Except for the assignment operators, all binary operators are left-associative, meaning that operations

8	are performed from left to right. For example, x + y + z is evaluated as (x + y) + z.
9	• The assignment operators and the conditional operator (?:) are right-associative, meaning that
10	operations are performed from right to left. For example, x = y = z is evaluated as x = (y = z).
11	Precedence and associativity can be controlled using parentheses. For example, x + y * z first multiplies
12	y by z and then adds the result to x, but (x + y) * z first adds x and y and then multiplies the result by z.

138.6 Statements

14C# borrows most of its statements directly from C and C++, though there are some noteworthy additions and

15modifications. The table below lists the kinds of statements that can be used, and provides an example for

16each.

Chapter 8 Language overview

	Statement	Example

	Statement lists and block	static void Main() {
	statements	F();
	statements	G();
		G();
		{
		H();
		I();
		}
		}

	Labeled statements and goto	static void Main(string[] args) {
	statements	if (args.Length == 0)
	statements	goto done;
		goto done;
		Console.WriteLine(args.Length);
		done:
		Console.WriteLine("Done");
		}

	Local constant declarations	static void Main() {
		const float pi = 3.14f;
		const int r = 123;
		Console.WriteLine(pi * r * r);
		}

	Local variable declarations	static void Main() {
		int a;
		int b = 2, c = 3;
		a = 1;
		Console.WriteLine(a + b + c);
		}

	Expression statements	static int F(int a, int b) {
		return a + b;
		}
		static void Main() {
		F(1, 2); // Expression statement
		}

	if statements	static void Main(string[] args) {
		if (args.Length == 0)
		Console.WriteLine("No args");
		else
		Console.WriteLine("Args");
		}

	switch statements	static void Main(string[] args) {
		switch (args.Length) {
		case 0:
		Console.WriteLine("No args");
		break;
		case 1:
		Console.WriteLine("One arg ");
		break;
		default:
		int n = args.Length;
		Console.WriteLine("{0} args", n);
		break;
		}
		}

	while statements	static void Main(string[] args) {
		int i = 0;
		while (i < args.Length) {
		Console.WriteLine(args[i]);
		i++;
		}
		}

C# LANGUAGE SPECIFICATION

	do statements	static void Main() {
		string s;
		do { s = Console.ReadLine(); }
		while (s != "Exit");
		}

	for statements	static void Main(string[] args) {
		for (int i = 0; i < args.Length; i++)
		Console.WriteLine(args[i]);
		}

	foreach statements	static void Main(string[] args) {
		foreach (string s in args)
		Console.WriteLine(s);
		}

	break statements	static void Main(string[] args) {
		int i = 0;
		while (true) {
		if (i == args.Length)
		break;
		Console.WriteLine(args[i++]);
		}
		}

	continue statements	static void Main(string[] args) {
		int i = 0;
		while (true) {
		Console.WriteLine(args[i++]);
		if (i < args.Length)
		continue;
		break;
		}
		}

	return statements	static int F(int a, int b) {
		return a + b;
		}
		static void Main() {
		Console.WriteLine(F(1, 2));
		return;
		}

	yield statements	static IEnumerable<int> FromTo(int a, int b) {
		if (a > b)
		yield break;
		for ( ; ; a++) {
		yield return a;
		if (a == b)
		break;
		}
		}

	throw statements and try	static int F(int a, int b) {
	statements	if (b == 0)
	statements	throw new Exception("Divide by zero");
		throw new Exception("Divide by zero");
		return a / b;
		}
		static void Main() {
		try {
		Console.WriteLine(F(5, 0));
		}
		catch(Exception e) {
		Console.WriteLine("Error");
		}
		}

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