C + + Syntax-the only difficulty for const and compound types

Summary at the bottom.

1.const and References

You can bind a reference to a constant, called a reference to a constant. You cannot assign a value to that reference.

Such as:

const int CI = 1024;

const int &ri = CI;

Interpretation: RI is a reference to CI. The const meaning of RI is to treat CI as a variable.

For constants, you can only use reference to constants, which is referred to as int &ri = CI; it is wrong because CI cannot be assigned a value, but may be assigned to an RI to affect the const qualification.

Therefore, they (the standard-setting person) create a reference to the constant reference way.

under high energy!!!

Above says:

Treat CI as a variable

Why?

2. Referencing a variable to a constant

int i = 2048;

Const &RI = i;

Interpretation: RI treats I as a variable and then references it

Effect: You cannot assign a value to an RI, but you can assign a value to I. Here I is the variable.

So: "Reference to a constant" is a reference | way |! For true constants, you must use this method for variables, which means that the code cannot be assigned by reference.

Think of it this way: you want to open an object that someone else can only read, but you can modify the value of this object.

int i; Your object

const int &RI = i; Pass this out.

You can bind to a constant reference: constant, variable ... Literal value, Expression!!!

int i = 5;

const int &RI1 = i; const int& bound to int variable

const int &RI2 = 9; Correct: The constant reference can be

const int &RI3 = r1 * 2; Correct: RI is a reference to a constant anyway

int &R4 = r1 * 2; Error: Normal citation is a fate.

R3 binding is the result of the expression at that time, it is a temporary amount.

Those things that are quoted and Const will be finished.

Nightmare, compound type There is another, pointer

3. Pointers and const

Good news: pointers and references are similar.

So:

Pointer to constant

const int i = 2;

const int *PCI = &i;

Pretty much, like, for constants, you must use pointers to constants.

Now point to the variable:

int II = 2;

const int *PCI = ⅈ

Similarly, you cannot assign a value after you dereference PCI, but you can assign a value directly to II.

Meal come!!!

4.const Pointer

Review: Pointers are objects, and references are not.

The const pointer means that the pointer object itself is a constant, allowing the pointer itself to be defined as an object.

Effect: The const pointer cannot change the address that points to the object.

1. Must initialize 2. Can only point to one place.

Placing * in front of the Const keyword indicates that the pointer itself is a constant.

int i = 0; Whether you want to refer to a variable or a constant

int *const CPI = &i; Will always point to I;

Big strokes:

A pointer to a constant and a constant pointer are separate.

const int *const CPCI = &i;

Parse: A constant pointer to a constant.

Property: 1. Must initialize (attributes from a constant pointer)

2. The point is no longer changed (attributes from a constant pointer)

3. You can refer to a constant or a variable (a property from a pointer to a constant)

5. Liberation

The definition above is too much for the mouth. Good, that's why C + + is difficult.

Defined:

Take a pointer to do an example

Top-Level const: Indicates that the pointer itself is a constant

Underlying const: Indicates that the object pointed to by the pointer is a constant (or as a constant)

Reasoning:

1. The reference does not have a top-level const, the reference is not an object, but a binding.

2. Constants of simple basic types are all top-level.

3. The pointer can be both a top-level const and an underlying const

Pit: Don't overlook the bottom cons T

int i;

const int *PC = &i;

int * p = pc; Error, the PC has the underlying const

Bottom-Level Const Usage Example: READ-only

int i;

const int *CI = &i; Get this out, read it.

About definition how to understand, personal view:

const INT | *const p;

Basic data type to Object | Declarator

Represents a pointer to a constant | Indicates that the pointer itself is a constant

Underlying const | Top-Level const

Note: The author second day learned, do not believe that someone can not understand

C + + Syntax-the only difficulty for const and compound types