Const for C + +

In C + + more powerful than in C!

#define定义常量, just simple text substitution, do not do type detection, error prone.

const int a = 10;

1 //defining a Const constant is the type int by default, and the const-defined symbolic constant has its own data type2 //compile more rigorous detection type Error! Safer than # define. Symbolic constants have addresses that can be pointed to, but cannot be modified by pointers. 3 //The const definition ends with a semicolon, which is treated as a statement. and # define does not write semicolons4 //it can be outside the function and inside the function. Only the scopes are different. 5 //C + + also supports # define definition of symbolic constants, and it is recommended to use a more secure const method6     intx =5;7     #defineT1 x + x8     #defineT2 T1-T19cout <<"T1 ="<< T1 <<"T2 ="<< T2 << Endl;

Explanation: #define只是简单的文本复制! t1=x+x=10 t2=x+x–x+x=x+x=10

Change to const to define symbolic constants: The result is 10 and 0

Const and Pointers

Pointer to constant (note the meaning of the pointer to the constant)

1     intx =5;2     Const int*p;//The pointer p itself is a variable, and *p (pointing to the content) does not necessarily have to point to a constant! 3     //Watch this! It is just that you cannot modify the *p, that is, the content that P points to is not modified by pointer p. 4p = &x;//the value of P itself can be modified5p =NULL;6 7     //*p = ten;//error C3892: "P": cannot assign a value to a constant8x =Ten;//the pointer p points to the content, not the constant, which can be modified. It just can't be modified by the pointer p. 

Constant pointer

1     int 5 ; 2     // pointer p points to a variable 3     int const p = &x; // The pointer p itself is a constant that cannot be modified and must be initialized at the time of definition!  4     ;   OK  5     //p = NULL; // error C3892: "P": cannot assign a value to a constant

Regular pointer to constant

1     intx =5;2     //The pointer p itself is a constant, and the content that P points to is also constant3     Const int*Constp = &x;//must be initialized the first time it is defined4     //p = NULL;//error C3892: "P": cannot assign a value to a constant5     //*p = ten;//error C3892: "P": cannot assign a value to a constant

Note: The use of const protection in function pointer parameters prevents modification of arguments, enhances security, and enhances readability.

Of course there are frequently used references.

Const for C + +