Const modifier Brief

Source: Internet
Author: User

Use of 1.const qualifiers

1) Define Const constants: Const can change an object to a constant, not modifiable (read-only type), and must be initialized at the time of definition. For example:

Const double mathpi = 3.141592653;

2) The parameters of the modifier function, the return value, and so on. Things that are modified by the const will no longer change;

3) If you are using variables from other files throughout your program:

If the variable is non-const//file_1.cppint months = 10;//file_2.cppextern int months;//const modified variable//file_1.cppextern const INT Dayperyear = 365;//file_2.cppextern const int dayperyear;

2. Pointer constant-constant pointer

1) Const int * P1: constant pointer (modifier type: pointer to read-only type)

2) int * Const P2: pointer constant (modifier pointer: constant of pointer type)

3) const int* Const P3: pointer constant pointing to constant

constant pointer: You can point to a constant or to a variable, you can change the point, but you cannot change the value of the point to the content;

Pointer constants: Must be initialized, constants cannot be assigned values. Pointers cannot be changed to point, and can be modified by pointers to the values in memory;

Constant pointer to constant: cannot change direction or modify content

3.CONST and macro define the difference between # define #

You can use const to define constants in C + +, or you can define constants by using # #:

1) The const constant is a data type, and the macro definition constant does not have a data type, so the compiler can perform type safety checks on the former and only character substitution for the latter;

2) const constants can limit the definition of a variable to a specific function or file, whereas a macro definition can only be in the head of a file;

3) const can be used for more complex types, such as arrays, structs, and classes.

Const modifier Description

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