Call by reference question

[badtwistofate]

I have a question regarding call by reference - essentially using a function i made and calling it in the main function. I'm passing 2 variables (pointers) into it and the value is copied in the corresponding function but the variable itself is not changed in the calling environment (main).

---

void somefunction(arg1, arg2, arg3, arg4, *ans1, *ans2)
// function does some arithmetic and spits out 2 output values/variables *ans1 and *ans2

---

NOT SHOWED is the header file that has the function prototype etc

int main(void)
{
int = arg1, arg2, arg3, *ans1, **ans11;
double = arg4, *ans2; **ans22

ans11 = &ans1
ans22 = &ans2

timediff(arg1, arg2, arg3, arg4, *ans1, *ans2);

printf("answers are %d and %d", ans11, ans22);

return 0;
}

---

I didn't copy my program in but made a close generic approximation version of it... hopefully that can help a little...

Thought the best way to do it is try and use a pointer to a pointer...

Any thoughts?

[laserlight]

What is your question? You might want to show us the smallest and simplest (compilable) program that demonstrates the problem instead of showing remarkably C-like pseudocode.

[matsp]

You can NEVER change anything inside a function that you haven't got the address of. In other words, if what you pass to a function is not a pointer to what you are trying to modify, you will only modify the variable that is local to the function.

For example:
pass a variable to modify an integer:

int func(int *p)
{
   *p = 7;
}

int main()
{
...
   int x = 3;
   func(&x);
...
}

Note that the same applies to pointers:

void func2(const char **ptr)
{
   if (x % 2)   // odd
   {
       *ptr = "Odd";
   }
   else
   {
       *ptr = "Even";
   }
}

--
Mats

[badtwistofate]

You can NEVER change anything inside a function that you haven't got the address of. In other words, if what you pass to a function is not a pointer to what you are trying to modify, you will only modify the variable that is local to the function.

For example:
pass a variable to modify an integer:

int func(int *p)
{
   *p = 7;
}

int main()
{
...
   int x = 3;
   func(&x);
...
}

Note that the same applies to pointers:

void func2(const char **ptr)
{
   if (x % 2)   // odd
   {
       *ptr = "Odd";
   }
   else
   {
       *ptr = "Even";
   }
}

--
Mats

Thank you.

Are you saying that I am on the right track with a pointer to a pointer?

[laserlight]

Are you saying that I am on the right track with a pointer to a pointer?

Yes, if your intention is really to change the pointer, not just what it points to.