C + + Learning: function pointers

Previously in the book to see the function pointers related to not much attention, but recently in the actual work has come in handy. So I studied it carefully again.

Declaration of function pointers

It is very simple to declare a function pointer by replacing the function name in the function declaration with a pointer:

C + + int  Test (int  para1, double  *para2); //function declaration  int  (*PF) (int  para1, Span class= "Hljs-keyword" style= "Color:rgb (249,38,114)" >double *para2); //function pointer declaration  

Note: You must enclose the parentheses in the declaration *pf , because the parentheses have a higher precedence than the * operator, so:

C + + int  (*PF) (int  para1, double  *para2); //A pointer to a function  int  *pf (int  para1, double  *para2); //a function that returns a pointer  

The next step in declaring a function pointer is to assign a value to a function pointer, which is to point a function pointer to a (which is consistent with the basic type of pointer), The function name of a function is the address of the function :

c/c++PF = test; int  (*PF1) (int  para1, double  *para2) = test; //can also complete initialization of   
 When the function pointer is declared

C++11 has the automatic type inference feature, which is a lot simpler:

auto pf = test;

Calling functions using function pointers

（*pf）The role is the same as the function name, so when you use （*pf） it, you only need to consider it as a functional name:

C + +int n = 0;double d = 0.0;int r = 0;r = (*pf)(n, &d);r = pf(n, &d); // 这种方式C/C++也是允许的

Array of function pointers

We may also need to use an array of function pointers, as shown in the following example:

C + +intTest1 (intPARA1,Double*PARA2);//Function declarationintTest2 (intPARA1,Double*PARA2);//Function declarationintTest3 (intPARA1,Double*PARA2);//Function declarationint(*pfarray[3])(intPARA1,Double*PARA2) = {test1, test2, test3};//function pointer array declaration and initializationr = *pfarray[0] (n, &d);//Function call

You can see that using a function pointer in this way is cumbersome, just imagine if the above function return value is a const pointer, and we want to declare the function pointer array as immutable, then const where should this be added? Here's another simple workaround, which is to simplify using typedef as we'll talk about it.

using typedef for simplification

C + + typedef  int  (*p_fun) (int  para1, double  *para2); //so that we can use a function pointer like a normal type  p_fun PF = Test;p_fun Pfarray[3 ] = {test1, test2, test3}; 

It ' s that easy!

Reference book: "C + + Primer Plus (6th edition) Chinese version"

C + + Learning: function pointers