A reference to pointers and pointers to C + + pointers

Show a reference to a pointer and pointer using pointers to modify the pointer passed to the method to better use it. (The pointer to the pointer is not a two-dimensional array.)

Why you need to use them

When we pass a pointer as a parameter to a method, we are actually passing a copy of the pointer to the method, or it can be said that the passing pointer is the value of the pointer passing.

If we have a problem modifying pointers inside a method, making changes in the method is just a copy of the modified pointer instead of the pointer itself, and the original pointer retains the original

The value. Let's use the code below to illustrate the problem:

int m_value = 1;void func (int *p) {    p = &m_value;} int main (int argc, char *argv[]) {    int n = 2;    int *PN = &n;    cout << *pn << Endl;    Func (PN);    cout << *PN <<endl;    return 0;}

Look at the output.

The output is two X 2

Using pointers to pointers

Show pointers as arguments using pointers

void func (int **p) {    *p = &m_value;    You can also allocate memory according to your needs    *p = new int;    **p = 5;} int main (int argc, char *argv[]) {    int n = 2;    int *PN = &n;    cout << *pn << Endl;    Func (&PN);    cout << *PN <<endl;    return 0;}

Let's take a look at the func (int **p) method

• P: Is a pointer pointer, where we do not modify it, otherwise we will lose the pointer to the address of the pointer
• *p: Is the pointer that is pointed to, is an address. If we modify it, the content of the pointer being directed is modified. In other words, we are modifying the *PN pointer in the main () method
• **p: Two times the dereference is the *pn of the main () method

Reference to Pointers

Look again at the reference code of the pointer

int m_value = 1;void func (int *&p) {    p = &m_value;    You can also allocate memory    p = new int according to your needs;    *p = 5;} int main (int argc, char *argv[]) {    int n = 2;    int *PN = &n;    cout << *pn << Endl;    Func (PN);    cout << *PN <<endl;    return 0;}

Take a look at the func (int *&p) method

• P: is a reference to a pointer, the *PN in the main () method
• *p: Is the content of the PN point in the main () method.

A reference to pointers and pointers to C + + pointers