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The "sharp" suffix has been used by a number of other. NET languages that are variants of existing languages, including J a. NET language also designed by Microsoft that is derived from Java 1. NET was called Eiffel ,  a name retired since the full Eiffel language is now supported.
The suffix has also been used for libraries , such as Gtk a. NET Framework 3. In particular:. However, the language specification does not state the code generation requirements of the compiler: that is, it does not state that a C compiler must target a Common Language Runtime, or generate Common Intermediate Language CIL , or generate any other specific format. C supports strongly typed implicit variable declarations with the keyword var , and implicitly typed arrays with the keyword new followed by a collection initializer.
C supports a strict Boolean data type , bool. Statements that take conditions, such as while and if , require an expression of a type that implements the true operator, such as the Boolean type. The only implicit conversions by default are those that are considered safe, such as widening of integers. This is enforced at compile-time, during JIT , and, in some cases, at runtime. No implicit conversions occur between Booleans and integers, nor between enumeration members and integers except for literal 0, which can be implicitly converted to any enumerated type.
Enumeration members are placed in their own scope. The C language does not allow for global variables or functions. All methods and members must be declared within classes. Static members of public classes can substitute for global variables and functions. Metaprogramming via C attributes is part of the language. A method in C is a member of a class that can be invoked as a function a sequence of instructions , rather than the mere value-holding capability of a class property.
Certain specific kinds of methods, such as those that simply get or set a class property by return value or assignment, do not require a full signature, but in the general case, the definition of a class includes the full signature declaration of its methods.
C has support for strongly-typed function pointers via the keyword delegate. Synchronized ] , and has support for mutually-exclusive locks via the keyword lock. C provides properties as syntactic sugar for a common pattern in which a pair of methods, accessor getter and mutator setter encapsulate operations on a single attribute of a class. Namespaces can be imported with the "using" syntax.
In C , memory address pointers can only be used within blocks specifically marked as unsafe , and programs with unsafe code need appropriate permissions to run.
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Most object access is done through safe object references, which always either point to a "live" object or have the well-defined null value; it is impossible to obtain a reference to a "dead" object one that has been garbage collected , or to a random block of memory. An unsafe pointer can point to an instance of an 'unmanaged' value type that does not contain any references to garbage-collected objects, array, string, or a block of stack-allocated memory. Code that is not marked as unsafe can still store and manipulate pointers through the System.
IntPtr type, but it cannot dereference them. Managed memory cannot be explicitly freed; instead, it is automatically garbage collected. Garbage collection addresses the problem of memory leaks by freeing the programmer of responsibility for releasing memory that is no longer needed. Checked exceptions are not present in C in contrast to Java. This has been a conscious decision based on the issues of scalability and versionability. This was a design decision by the language's lead architect to avoid complication and simplify architectural requirements throughout CLI.
When implementing multiple interfaces that contain a method with the same signature, i.
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However, unlike Java , C supports operator overloading. C has the ability to utilize LINQ through the. NET Framework. Though primarily an imperative language, C 2. C has a unified type system. A unified type system implies that all types, including primitives such as integers, are subclasses of the System.
Object class. For example, every type inherits a ToString method. CTS separates data types into two categories: . Instances of value types do not have referential identity nor referential comparison semantics - equality and inequality comparisons for value types compare the actual data values within the instances, unless the corresponding operators are overloaded.
Value types are derived from System. ValueType , always have a default value, and can always be created and copied. Some other limitations on value types are that they cannot derive from each other but can implement interfaces and cannot have an explicit default parameterless constructor. Examples of value types are all primitive types, such as int a signed bit integer , float a bit IEEE floating-point number , char a bit Unicode code unit , and System. DateTime identifies a specific point in time with nanosecond precision.
Other examples are enum enumerations and struct user defined structures.
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In contrast, reference types have the notion of referential identity - each instance of a reference type is inherently distinct from every other instance, even if the data within both instances is the same. This is reflected in default equality and inequality comparisons for reference types, which test for referential rather than structural equality, unless the corresponding operators are overloaded such as the case for System.
In general, it is not always possible to create an instance of a reference type, nor to copy an existing instance, or perform a value comparison on two existing instances, though specific reference types can provide such services by exposing a public constructor or implementing a corresponding interface such as ICloneable or IComparable.
Examples of reference types are object the ultimate base class for all other C classes , System. String a string of Unicode characters , and System. Array a base class for all C arrays. Boxing is the operation of converting a value-type object into a value of a corresponding reference type. Unboxing is the operation of converting a value of a reference type previously boxed into a value of a value type. A boxed object of type T can only be unboxed to a T or a nullable T.
The C specification details a minimum set of types and class libraries that the compiler expects to have available. In addition to the standard CLI specifications, there are many commercial and community class libraries that build on top of the. NET framework libraries to provide additional functionality. The following is a very simple C program, a version of the classic " Hello world " example:. The above line imports all types in the System namespace. For example, the Console class used later in the source code is defined in the System namespace, meaning it can be used without supplying the full name of the type which includes the namespace.
Above is a class definition. Everything between the following pair of braces describes Program. This declares the class member method where the program begins execution. NET runtime calls the Main method.
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Note: Main may also be called from elsewhere, like any other method, e. The static keyword makes the method accessible without an instance of Program. Each console application's Main entry point must be declared static. Otherwise, the program would require an instance, but any instance would require a program. To avoid that irresolvable circular dependency , C compilers processing console applications like that above report an error, if there is no static Main method.