3. Function pointers and pointer functions

Function pointers and pointer functions

A function pointer

A function pointer is a pointer , Point to a function , The return value and parameter list of the pointed function must be the same as The return value of pointer definition is the same as the parameter list .

For example, the following code ：

 #include<stdio.h>
 
 void pp()
 {
    
         printf("this is function pp!\n");
 }
 void ppp()
 {
    
         printf("this is function ppp!\n");
 }
 int main(void)
 {
    
         void (*p)();
         p = pp;
         p();
         p = ppp;
         p();
         return 0;
 }

It defines a point The return value is void, Function pointer with empty argument list , And two functions are defined pp and ppp, And then they will p Point to these two functions and call the function . This is the function pointer .*p The surrounding brackets must not be omitted , Otherwise it will be wrong . Use （） after p With the first * combination , therefore p It's a pointer .

Note that when assigning values above, the function name is directly assigned to the pointer , We all know that the pointer points to the address , The previous pointer to the variable needs to add a & This address symbol , When the function pointer points to a function, you don't need , This shows that the function name is actually an address ,

printf("%p\n",pp);
printf("%p\n",&pp);

We can try printing the above two values again , One is printing pp Value , One is printing pp The address of , We can find that these two values are the same , That is to say whether pp still &pp All represent addresses , So the assignment of the previous pointer can not only be p = pp; It can also be p = &pp; Of course, we usually use p = pp; It's not convenient to lose one symbol ？

Pointer function

The pointer function is a function , The return value of this function is a pointer .

for example int* f(int a, int b); Is the definition of a pointer function , The return value of this function must be a int Pointer to type .

（） Has a higher priority than *, therefore f With the first （） combination ,f It's a function .

Function pointer array

seeing the name of a thing one thinks of its function , This is an array , Every element in the array is a function pointer , A function pointer is a pointer to a function . All elements in an array must be of the same type , So all function pointers in the array must point to functions of the same type .

int (*p[10])(int a, int b);