On Thu, Nov 3, 2011 at 1:43 AM, Tomek CEDRO <tomek.ce...@gmail.com> wrote:
> Hello Andreas :-)
>
> On Thu, Nov 3, 2011 at 12:36 AM, Andreas Fritiofson
> <andreas.fritiof...@gmail.com> wrote:
> > This won't even compile. You pass a pointer-to-int, but swd_bus_read_ack
> > expects a pointer-to-pointer-to-char.
>
> naah this is only typo in mind-shortcut, code builds well, but i dont
> get it why i cannot use single pointer to pass back a memory location
> to function caller... this is what pointers exist..
>
>
Ah, well, but c passes parameters by value, to get out parameters you have
to go via a pointer.
Consider:
void foo(int x)
{
x++;
}
int main(void)
{
int a = 3;
foo(a);
return 0;
}
Did you expect the value of a to change after the call to foo? No, didn't
think so. You'd have to do this instead:
void foo(int *x)
{
*x++;
}
int main(void)
{
int a = 3;
foo(&a);
return 0;
}
Here a gets the value 4 after the call to foo.
Now change the variable type to a pointer instead of an integer:
void foo(int **x)
{
*x++;
}
int main(void)
{
int *a = &bar;
foo(&a);
return 0;
}
Here a points to the integer following bar after the call to foo. It's
exactly the same concept, just a change of variable type from int to int*.
Note that &a is now a double pointer, nothing magic here. Do the same
variable type change in the first, non-functional, example and convince
yourself that that wont work either.
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