Getting the address of a member function, using CPP

Question

I am working on a school assignment in which I need to build a thread library. I need pc to hold the address of the given Thread object's run() function. When I try to cast a member function pointer to address_t (which is really unsigned long int) I get this error

../main.cpp: In function ‘void setup(Thread&)’:

../main.cpp:77:22: error: invalid cast from type ‘int (Thread::*)()’ to type ‘address_t {aka unsigned int}’

make: * [main.o] Error 1

Here's the function where I get the error:

void setup(Thread &thread)
{
    address_t sp, pc;

    sp = (address_t)stack1 + STACK_SIZE - sizeof(address_t);
    int (Thread::*temp)() = &Thread::run;
    pc = (address_t) temp; // @@ LINE 77 @@

    sigsetjmp(jbuf[0],1);
    (jbuf[0]->__jmpbuf)[JB_SP] = translate_address(sp);
    (jbuf[0]->__jmpbuf)[JB_PC] = translate_address(pc);
    sigemptyset(&jbuf[0]->__saved_mask);
}

A few clarification:

Thread is a class I wrote, currently doing nothing. It as a int run(void) as its "main" function. address_t, as I said, is typedef unsigned long int

Any ideas as to why I get this error? thanks

Don't use non-static member functions this way. Use non-member functions or static member functions. You can't invoke a member function without a class instance. — David Schwartz
– David Schwartz, Commented Apr 21, 2012 at 12:30

UmNyobe · Accepted Answer · 2012-04-21 12:26:04Z

4

I don't think you can do that.

void pointers are pointers to data, and function pointers point to functions. The language does not require functions and data to be in the same address space, so, by way of example and not limitation, on architectures that have them in different address spaces, the two different pointer types will not be comparable.

Take a look at this nice faq. If you cannot convert to void*, then you cannot convert to int or long int

answered Apr 21, 2012 at 12:26

UmNyobe

23.1k10 gold badges64 silver badges90 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Konrad Rudolph · Accepted Answer · 2012-04-21 12:30:04Z

1

This doesn’t work for two reasons:

function pointers are not compatible with void* (se UmNyobe’s answer), and
in order to use member functions as the thread entry you’d need to store a this pointer as well.

Since you’re using C++ you’ve got a few possibilities though:

Use a base class thread_base defining a virtual function as the thread entry point.
Use a functor as the thread entry point.

In either case you’d need to store this information somewhere and invoke it using the operating system’s thread library.

answered Apr 21, 2012 at 12:30

Konrad Rudolph

549k142 gold badges967 silver badges1.3k bronze badges

Collectives™ on Stack Overflow

Getting the address of a member function, using CPP

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related