Function returning pointer to itself

aijazbaig1 · #1 10-Jul-2009, 11:27

Hello,

I was reading this famous C faq by steve summit where it was said that it is impossible for a function to return a pointer which points to a function of the same type. Mindboggling

? betcha!

nonetheless it also suggested 'wrapping' a struct around such a function and then returning the struct would work here. So i tried with:

CPP / C++ / C Code:

#include <stdio.h>
#include <stdlib.h>

typedef struct {
    mystruct *func(); // line 5
} mystruct;

int main()
{
    printf("address of func is %p,using func %p\n",&func(),func); //line 10
    printf("address of struct is %p\n",&mystruct); //line 11
    return 0;
}

and I get the following compiler errors on a GCC based system:

Code:

main.c:5: error: expected specifier-qualifier-list before ‘mystruct’
main.c: In function ‘main’:
main.c:10: warning: implicit declaration of function ‘func’
main.c:10: error: lvalue required as unary ‘&’ operand
main.c:11: error: expected expression before ‘mystruct’
make: *** [main.o] Error 1

Then I tried with this as the solution alternatively suggested typecasting. My solution doesn't use typecasting but I thought would work anyways but it doesn't:

CPP / C++ / C Code:

void func();
func *func1();

int main()
{
    return 0;
}

and ended up with:

Code:

main.c:9: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘*’ token
make: *** [main.o] Error 1

A slight modification including typecasting yields:

CPP / C++ / C Code:

void func();
func (func*)*func1();

int main()
{
    return 0;
}

And the results are:

Code:

main.c:9: error: expected ‘)’ before ‘*’ token
make: *** [main.o] Error 1

I do not know how to use a typecast or a struct to create such a function. Input would be appreciated

davekw7x · #2 10-Jul-2009, 16:46

Quote:

Originally Posted by aijazbaig1

...
I was reading this famous C faq by steve summit

The thing about lists of Frequently Asked Questions is that they usually post some answers with a little insight thrown in: http://c-faq.com/decl/recurfuncp.html

For examples of declarations and uses of function pointers in the same FAQ, see: http://c-faq.com/decl/pfitypedef.html and http://c-faq.com/ptrs/funccall.html

Regards,

Dave

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Function returning pointer to itself

Re: function returning pointer to itself