| 5.8. Pointers to functions | ||
|---|---|---|
 | Chapter 5. Pointers in C |  |
| 5.8. Pointers to functions | ||
|---|---|---|
| | Chapter 5. Pointers in C | |
A function pointer is a variable that stores the address of a function. This function can be called later,
through the pointer. This type of construction is useful as encapsulates behavior, which can be called through a pointer.
Let's see how it works with a simple example that creates a pointer to a function and invokes do_print:
1 2 3 4 5 6 7 8 9 10 11 | #include <stdio.h>
void do_print()
{
printf("Printing a message\n");
}
int main()
{
void (*ptr_funct)(void)=do_print;
ptr_funct(); //It calls do_print
return 0;
} |
Function pointers are also used for callback functions. The following code snippet shows an example where a function
receives as a parameter a function pointer, which invokes when it has completed execution. It also prints out the memory addresses
occupied by the functions, which is printed with the %p include in the printf function.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 | #include <stdio.h>
void printf_hello(int x)
{
printf( "[*HELLO__] Hello number %d\n", x);
}
void printf_bye(int x, void (*ptr_func)())
{
printf( "[*BYE____] Bye, bye number %d\n", x);
if(ptr_func!=NULL)
{
ptr_func(); //Using the pointer to callback
}
}
void funct_call_back()
{
printf( "[*CALLBACK] Callback invoked\n");
}
int main()
{ // Two pointers to functions
void (*ptr_funct_1)(int)=NULL;
void (*ptr_funct_2)(int, void (*call_back_funct)() )=NULL;
//First pointer
ptr_funct_1 = printf_hello;
printf("[*MAIN_] First pointer is %p\n",ptr_funct_1);
ptr_funct_1(3);
//Second pointer
ptr_funct_2 = printf_bye;
printf("[*MAIN_] Using a callback function \n",ptr_funct_2);
ptr_funct_2(3,funct_call_back);
return 0;
} |
| |  | |
| 5.7.4. Self-assessment questions |  | 5.9. Further reading |