Usage of pointers [2]

 

 

1.A pointer to a pointer variable is called a pointer.

Definition form: Type ** variable name

For example: int I, * p, ** q;

 

I = 30;

P = & I;

Q = & p; // pointer q points to p pointer

2.Pointers and functions

 

A. the pointer is used as a function parameter.

B. pointer Functions

C. pointer to function

 

A. Example:

Swap (int * pa, int * pb)

{

Int p;

P = * pa;

* Pa = * pb;

* Pb = p;

}

 

Main ()

{

Int a, B;

Int * p1, * p2;

Scanf ("% d", & a, & B );

P1 = & a, p2 = & B;

If (a <B)

Swap (p1, p2 );

Printf ("\ n % d, % d \ n", a, B );

}

Input from keyboard: 5 10

Output: 10, 5

Let's look at the following example.

Main ()

{

Int a, B; int * p1, * p2;

Void swap (int * pa, int * pb );

Scanf ("% d, % d, & a, & B );

P1 = & a; p2 = & B;

If (a <B)

Swap (p1, p2 );

Printf ("\ n % d, % d \ n", a, B );

}

 

Void swap (pa, pb)

{

Int * pa, * pb;

Int * p;

P = pa;

Pa = pb;

Pb = p;

}

Input from keyboard: 5 10

Output: 10, 5

Pointer function:

A function can return integer, real, and balanced values, or pointer-type data, that is, an address.

The return value is a pointer function.

The general definition form is:

Type identifier * function name (parameter table );

Example: int * a (int x, float y)

{......}

A is the function name. After calling it, you can get a pointer (Address) to the integer data)

X and y are the form parameters of function.

There is a * in front of this function, indicating that the sub-function is a pointer type function.

For example:

Main ()

{

Int a, B, * p;

Int * max (int, int );

Scanf ("% d", & a, & B );

P = max (a, B );

Printf ("max = % d", * p );

}

Int * max (int x, int y)

{If (x <y)

Return (& y );

Else return (& x );

 

Pointer to function:

The function name indicates the function entry address.

Pointer to a function: type (* pointer variable name )();

Example: int (* p )();

Example:

Int max (...)

{......}

Int (* p) (); // defines the pointer variable pointing to the Function

P = max; // enables p to point to the entry address of the max function. You can call max through (* p) ().

Example:

Main ()

{

Int max ();

Int (* p) (); // defines the function pointer

Int a, B, c;

P = max;

Scanf ("% d \ n", & a, & B );

C = (* p) (a, B); // call a function

Printf ("a = % d, B = % d, max = % d", a, B, c );

}

Int max (x, y)

{

Int z;

If (x> y) z = x;

Else z = y;

Return (z );

}