4 New Types of conversions in C ++ and 5. c4 types of conversions

4 New Types of conversions in C ++ and 5. c4 types of conversions

1. First, let's review the forced conversion of C.

As we all know, when compiling a forced conversion in C language, the compiler will not check whether the conversion is successful, and the compilation will be correct.

For example:

#include "stdio.h"struct Position{int x;int y;};int main(){ int i; struct Position *p; i=0x123456; p=(struct Position *)i; printf("px=%d,py=%d\n",p->x,p->y);}

Shows the output result:

 

It can be seen that the segment error occurs only when the code is run.

When C codeThousands of linesIf this problem occurs, it is very difficult to find.

 

2. New type conversion of C ++

Therefore, in C ++4TypeForced type conversion

2.1 static_cast (static type conversion)

• UsedBasic DataConversions between types (char, int, const int, etc)
• Cannot be usedConversion between basic data type pointers (char *, int *, etc)
• UsedClass objects with inheritance relationshipsConversion
• UsedClass pointerConversion

For example:

Int I = 0x45; char c = 'C'; c = static_cast <char> (I); // char * pc = static_cast <char *> (& I ); // This row is incorrect and cannot be used for conversion between basic pointers

 

 

2.2 const_cast (non-constant type conversion)

• UsedRemoveVariableRead-only attribute
• And the forced conversion type must bePointer*OrReference&

For example:

Const int x = 1; // const: defines a constant x const int & j = 2; // const reference: define a read-only variable jint & p1 = const_cast <int &> (x); // forcibly convert int & int * p2 = const_cast <int *> (& j ); // force convert int * // int p3 = const_cast <int> (j); // This row is incorrect. The normal data type p1 = 3 cannot be converted; * p2 = 4; printf ("x = % d, j = % d \ n", x, j); printf ("p1 = % d * p2 = % d \ n", p1, * p2 );

Output result:

x=1   j=4p1=3  *p2=4

From the output result, we can see that only j content is changed when p1 and p2 are modified. It is a read-only variable because the variable j is referenced and defined by const.

 

2.3 dynamic_cast (dynamic type conversion)

• UsedClass pointers with inheritance relationshipsInter-Domain Conversion
• UsedCross-correlation class pointerInter-Domain Conversion
• WithType checkFunctions
• YesVirtual FunctionsSupport
• Cannot be usedConversion between basic data type pointers (char *, int *, etc)

 

2.4 reinterpret _ cast (Interpretation type conversion)

• UsedAll pointersForced conversion

(Interpretation refers to re-interpreting the data to be converted)

For example:

Int I = 0; char j = 'C'; int * p1 = reinterpret_cast <int *> (& I); char * p2 = reinterpret_cast <char *> (& j ); // int p3 = reinterpret_cast <int> I; // This row is incorrect. Normal data type cannot be converted.