Solution for Exercise 09_06-prtstruct.c

09_06-prtstruct.c

#include <stdio.h>

char *hello(void)
{
	return("Hello, ");
}

char *world(void)
{
	return("world!\n");
}

int main()
{
	struct msg {
		char *(*f1)();
		char *(*f2)();
	} func;

	func.f1 = &hello;
	func.f2 = &world;

	printf("%s%s",func.f1(),func.f2());

	return 0;
}

Output

Hello, world!

Notes

* The first major change is the data type for both functions. In the source code file 09_05-structptr.c (in the book), these are both void functions. In the solution file, they must be char * (character pointers). Each returns the address of a string.

* To properly type the member sof the msg structure, each must be set as a character pointer function that requires no arguments: char *(*f1)() and char *(f2)()

* Yes you, can specify void in the pointer/function members: char *(*f1)(void) and char *(f2)(void)

* The assignments may have thrown you. Because the functions return a pointer, they must be assigned to the address of an address: func.f1 = &hello; and func.f2 = &world; The & (address-of) operator is required because the function itself is an addresss but it returns an address. So it's an address of an address, which is that double-pointer nonsense.

* Refer to the book for more details on dealing with double pointers.

Exercise 09_09-qsortptrs.c →