4 types of coercion type conversions in C + +

Four types of coercion for C + + are converted to: static_cast, Const_cast, reinterpret_cast, and dynamic_cast

General form of type conversion: Cast-name

Static_cast

Any explicitly defined type conversions can use static_cast as long as they do not contain the underlying const;

Double slope = static_cast

Note:
Top-Level const: Indicates that the pointer itself is a constant. such as: int *const p;
Underlying const: Indicates that the object that the pointer refers to is a constant. such as: int const *p;

Const_cast

This operator can only change the underlying const of an operand.

#include<iostream>    using namespace std;int main()  {      const char *pc=" HDU";      char *p=const_cast<char *>(pc);  //正确，      cout<<"hello"<<p<<endl;      return 0;  }  

Note: Here can only use const_cast, but not with static_cast;

Reinterpret_cast

Typically, the bit patterns of the operands provide a lower level of re-interpretation.
Note:
1. Convert between pointers, convert one type of pointer to another type of pointer, irrelevant type;
2. Converts the pointer value to an integer number, but not to a non-pointer-type conversion.

dynamic_cast

Pointers and references for objects only, cannot be used for casting of built-in base data types.
If you use dynamic_cast to convert, you must have a virtual function in the base class, or the compilation will not pass.
Run-time type recognition, a pointer or reference that is used to safely convert a pointer or reference to a base class to a derived class.

dynamic_cast the pointer, fails to return NULL, successfully returns the normal cast of the object pointer;
Dynamic_cast the reference, the failure throws an exception bad_cast, which successfully returns the normal cast object reference.

For an "up conversion" (that is, a derived class pointer or reference type is converted to its base class type), either the pointer or the reference upward conversion is safe.
There are two scenarios for "down transition":
1, the base class pointer refers to the object is a derived class type, the conversion is safe;
2, the base class pointer refers to the object is the base class type, in this case dynamic_cast at run time to do the check, the conversion fails, the return result is 0;
On the reference, dynamic_cast is still often used for "safe downward transformation". As with pointers, the downward transformation of a reference can also be divided into two cases, unlike pointers, where there is no null reference, so a Bad_cast exception is thrown when the referenced dynamic_cast detection fails.

#include <iostream>#include <cstring>using namespace std;class A{public:    virtual void f()    {       cout << "hello" << endl;    }}; class B: public A{public:    void f()    {        cout << "hello2" << endl;    } };int main(){    A* a1=new B;//a1是A类型的指针指向一个B类型的对象    A* a2=new A;//a2是A类型的指针指向一个A类型的对象    B* b;        b=dynamic_cast<B*>(a1);    //结果为not null，向下转换成功，a1之前指向的就是B类型的对象，所以可以转换成B类型的指针。    if(b==NULL)        cout<<"null"<<endl;    else        cout<<"not null"<<endl;        b=dynamic_cast<B*>(a2);//结果为null，向下转换失败    if(b==NULL)        cout<<"null"<<endl;    else        cout<<"not null"<<endl;    return 0;}

Summarize

Basic type conversion with static_cast.
Go to the const attribute with const_cast.
Different types of pointer-type conversions with Reinterpreter_cast.
A type conversion between polymorphic classes is used with Daynamic_cast.

4 types of coercion type conversions in C + +

Four types of coercion for C + + are converted to: static_cast, Const_cast, reinterpret_cast, and dynamic_cast

General form of type conversion: Cast-name

Static_cast

Any explicitly defined type conversions can use static_cast as long as they do not contain the underlying const;

Double slope = static_cast

Note:
Top-Level const: Indicates that the pointer itself is a constant. such as: int *const p;
Underlying const: Indicates that the object that the pointer refers to is a constant. such as: int const *p;

Const_cast

This operator can only change the underlying const of an operand.

#include<iostream>    using namespace std;int main()  {      const char *pc=" HDU";      char *p=const_cast<char *>(pc);  //正确，      cout<<"hello"<<p<<endl;      return 0;  }  

Note: Here can only use const_cast, but not with static_cast;

Reinterpret_cast

Typically, the bit patterns of the operands provide a lower level of re-interpretation.
Note:
1. Convert between pointers, convert one type of pointer to another type of pointer, irrelevant type;
2. Converts the pointer value to an integer number, but not to a non-pointer-type conversion.

dynamic_cast

Pointers and references for objects only, cannot be used for casting of built-in base data types.
If you use dynamic_cast to convert, you must have a virtual function in the base class, or the compilation will not pass.
Run-time type recognition, a pointer or reference that is used to safely convert a pointer or reference to a base class to a derived class.

dynamic_cast the pointer, fails to return NULL, successfully returns the normal cast of the object pointer;
Dynamic_cast the reference, the failure throws an exception bad_cast, which successfully returns the normal cast object reference.

For an "up conversion" (that is, a derived class pointer or reference type is converted to its base class type), either the pointer or the reference upward conversion is safe.
There are two scenarios for "down transition":
1, the base class pointer refers to the object is a derived class type, the conversion is safe;
2, the base class pointer refers to the object is the base class type, in this case dynamic_cast at run time to do the check, the conversion fails, the return result is 0;
On the reference, dynamic_cast is still often used for "safe downward transformation". As with pointers, the downward transformation of a reference can also be divided into two cases, unlike pointers, where there is no null reference, so a Bad_cast exception is thrown when the referenced dynamic_cast detection fails.

#include <iostream>#include <cstring>using namespace std;class A{public:    virtual void f()    {       cout << "hello" << endl;    }}; class B: public A{public:    void f()    {        cout << "hello2" << endl;    } };int main(){    A* a1=new B;//a1是A类型的指针指向一个B类型的对象    A* a2=new A;//a2是A类型的指针指向一个A类型的对象    B* b;        b=dynamic_cast<B*>(a1);    //结果为not null，向下转换成功，a1之前指向的就是B类型的对象，所以可以转换成B类型的指针。    if(b==NULL)        cout<<"null"<<endl;    else        cout<<"not null"<<endl;        b=dynamic_cast<B*>(a2);//结果为null，向下转换失败    if(b==NULL)        cout<<"null"<<endl;    else        cout<<"not null"<<endl;    return 0;}

Summarize

Basic type conversion with static_cast.
Go to the const attribute with const_cast.
Different types of pointer-type conversions with Reinterpreter_cast.
A type conversion between polymorphic classes is used with Daynamic_cast.

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4 types of coercion type conversions in C + +