Initial look function pointer

We usually know that a pointer is used to store the address of a variable. This variable has the same data type as the pointer type. In addition to this function, the pointer can also point to the address of a function to call the function to be pointed.

(1) function pointer declaration:

Int (* pfun) (double, int );

In this way, a function pointer pointing to the parameter type of double and int is declared.

Function pointers are generally composed of three parts:

1. Point to the return type of the Function

2. pointer name

3. Type of the parameter pointing to the Function

(2) how to point to a function:

Long sum (long a, long B );

Long (* pfun) (long, long) = sum;

In this way, the * pfun function pointer is used to point to the sum function.

Simple Example:

[Cpp]
# Include <iostream>
 
Using std: cout;
Using std: endl;
 
Long sum (long a, long B );
Long product (long a, long B );
 
Int main ()
{
Long (* pdo_it) (long, long );
Pdo_it = product;
Cout <endl <"3*5 =" <pdo_it (3, 5 );
 
Pdo_it = sum;
Cout <endl <"3 * (4*5) + 6 =" <pdo_it (product (3, pdo_it (4, 5), 6 );
Cout <endl;
 
System ("pause ");
Return 0;
}
 
Long product (long a, long B)
{
Return a * B;
}
 
Long sum (long a, long B)
{
Return a + B;
}
The result is:

 

(3) function pointer as real parameter:
Because "pointer to function" is a completely reasonable type, a function can have a form parameter of the type as a function pointer. Then, such a function calls the function pointed to by the real parameter.

Example:

[Cpp]
# Include <iostream>
 
Using std: cout;
Using std: endl;
 
Double squared (double );
Double cubed (double );
Double sumarray (double array [], int len, double (* pfun) (double ));
 
Int main ()
{
Double array [] = {1.5, 2.5, 3.5, 4.5, 5.5, 6.5, 7.5 };
Int len (sizeof array/sizeof array [0]);
 
Cout <endl <"Sum of Squared =" <sumarray (array, len, squared );
Cout <endl <"Sum of cubed =" <sumarray (array, len, cubed );
Cout <endl;
 
System ("pause ");
Return 0;
}
 
Double squared (double x)
{
Return x * x;
}
 
Double cubed (double x)
{
Return x * x;
}
 
Double sumarray (double array [], int len, double (* pfun) (double ))
{
Double total (0.0 );
For (int I = 0; I <len; ++ I)
{
Total + = pfun (array [I]);
}
Return total;
}
The result is:

(4) function pointer array:

Assume there are three functions:

Double add (double, double );

Double mul (double, double );

Double div (double, double );

Double (* pfun [3]) (double, double) = {add, mul, div };

You can call:

Pfun [1] (1.5, 5.5 );