Focus on C + + details--Universal const qualifier and Pointer __c++

Do not remember who said, can use the const when possible to use the Const. Indeed, Const makes a great contribution to increasing the robustness of the program, but the const modifier pointer is noteworthy.

A pointer to a const object;

If the pointer is to a const object, it is clear that the const value it points to is not changed by the pointer. To ensure this feature, the C + + language enforces that pointers to the Const object must also have a const attribute.

const DOUBLE = 1.0;

const double *CPT;

cpt=&d;

Why the const-type pointer variable can be assigned a value again. In fact, the CPT here is a pointer to a double type const object, which is defined by the type of object that the CPT pointer points to, not the CPT itself. In other words, CPT itself is not a const. Therefore, CPT does not need to be initialized at the time of definition, allowing the CPT to be assigned a value, pointing to another const object.

Note: You can assign an ordinary object's address to a pointer to a const object, but you cannot assign a const object address to an ordinary type pointer, otherwise a compilation error occurs. You cannot modify the underlying object with a pointer to a const object. Whether the const pointer points to an object that is not a const type, the system treats all objects it refers to as a const, limited to the const object of the pointer (through which the value cannot be modified);

Two. Const pointer;

In addition to pointers to the const object, the C + + language provides a const pointer--its value cannot be modified.

int inum = 1;

int * Const icpt=&inum;

The ICPT here is the const type--no longer pointing to other objects. Any attempt to assign values to the const pointer results in a compilation error. It is worth noting that the const type of the pointer itself does not indicate whether the pointer can be used to modify the value of the object it points to. Whether the value of the object that the pointer refers to can be modified depends entirely on the type of object.

int inum = 5;

int * Const icpt=&inum;

*icpt=4;//here is perfectly OK, because inum is a normal variable.

Three. Point to const object Const pointer;

Here is the combination of the two cases where the const type pointer points to a const type object.

const double pi=3.14;

Const DOUBLE * Const pt=π

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