Summary of C + + technical issues-No. 0 type conversion

Start today with a summary of how C + + often uses technology.

Reference books: "C++primer", "C + + object Model", "design Mode", "Windows core Programming", "STL decryption".

1. detailed meaning of four cast of static_cast

C + + type conversions: implicit conversions and explicit conversions.

Explicit conversions:static_cast,dynamic_cast,reinterpret_cast, Const_cast.

1.1. static_cast

How to use:static_cast<type-id> (expression)

Description: The operator converts expression to the type-id type, but does not perform a type check to guarantee the security of the conversion.

Source: Why do I need static_cast type casting?

(1) Void pointer , other type of pointer.

(2) Change the usual standard conversions.

(3) Avoid ambiguity that may occur in multiple conversions.

Several ways to use:

(1) A pointer or reference conversion between a base class and a subclass in a class hierarchy.

It is safe to make an upstream conversion (a pointer or reference to a class is converted to a base class).

When you make a downstream conversion (a pointer or reference to a base class is converted to a subclass), it is unsafe because there is no dynamic type checking.

(2) For conversions between basic data types, such as converting an int to char .

The security of such conversions also needs to be ensured by the developer.

(3) convert the void pointer to a pointer of the target type (unsafe).

(4) Convert any type of expression to void type.

1.2. dynamic_cast

How to use:dynamic_cast<type-id> (expression)

Description: This operator converts expression to an object of type Type-id. Type-id must be a pointer, reference, or void* to a class .

A pointer or reference to a base class type that is safely converted to a pointer or referral of a derived type.

Run two operations at a time. It first verifies that the requested conversion is valid, that only the conversion is valid, and that the operation characters the actual conversion.

Flow chart.

Source: Why do I need to dynamic_cast?

Simply put, when you can't use the virtual function. You can only do this if you cannot change the source code.

Thedynamic_castandstatic_cast effects are the samewhen upstream conversions are made between class hierarchies, and when the downstream conversion is performed, thedynamic_cast is a feature that has type checking.

1.3. reinterpret_cast

How to use:reinterpret_cast<type-id> (expression)

Description:Type-id must be a pointer, reference, arithmetic type, function pointer, or member pointer.

How to use: it is able to convert a pointer to an integer, or to do the opposite.

1.4. Const_cast

How to use:const_cast<type-id> (expression)

Description: This operator is used to change the const or volatile property of a type .

A constant pointer or reference is converted to a pointer or reference, and still points to the original object.

Constant objects are converted to very mass objects.

Personal understanding: Personal infrequently used, this method of use violates the original design intent.

Demo Sample:

Class B {public:int m_inum;}; void foo () {    const B B1;    B1.m_inum = 1000;//Compilation failed because B1 is a constant    b& b2=const_cast<b&> (B1);    The M_inum value of B2.M_INUM=200;//FINE,B1 and B2 is 200}

Summary of C + + technical issues-No. 0 type conversion