Creating a null type (was pointer)

[babazaroni]

I need to pass a null to a function that has a nullable type for an argument.

The XMOS programming guide talks about nullable types but fails to mention how one creates a null pointer. ARG!

I've tried passing 'null','NULL' and '0' to the function but get undeclared for the nulls and invalid argument for the '0'.

Simple example:

void function(server an_if ?i_an_if){
}

main()
{
function(NULL); // undeclared error for NULL
}

So, how does one pass a null pointer to a function that has a nullable argument?

[srinie]

#include <stdio.h>

void function(int * unsafe a){
if (a == null)
printf("null pointer!!!");
}

int main()
{
function(null); // undeclared error for NULL
}


/* compiled using 14.0.3 Community xTIMEcomposer */

C:\Users\xmos_addict>xsim C:\Users\xmos_addict\null_pointer_eg\bin\null_pointer_eg.xe
null pointer!!!

[srinie]

Another version tried using the interface method:
-------------------------------------------------------


#include <print.h>
#include <stdio.h>

interface my_interface {
void msg(int * p);
};

void task1(client interface my_interface c)
{
int a[5] = {0,1,2,3,4};
int *p = null; //&a[0];
{c.msg(p);}
printf("task1 - bye\n");
}

void task2(server interface my_interface c)
{
select {
case c.msg(int * p):
if (p != null ) {printintln(*p);
printintln(*(p+2));}
break;
}
printf("task2 - bye\n");
}

int main() {
interface my_interface c;
par {
task1(c);
task2(c);
}
return 0;
}


====================

C:\Users\srini>xsim C:\interfaceparams.xe
task2 - bye
task1 - bye



Reference: Adapted from AN10025

[babazaroni]

Thanks, srinie, for the replies. I should not have said null pointer but null type. I've changed title.

The '?' in front of the arguement type means that it is nullable and can be tested with the isnull macro, like below:

void function(server an_if ?i_an_if)
{
if (!isnull(i_an_if) do_something(i_an_if);
}

Now I need to find out how to pass a null type.

[babazaroni]

The problem has been found.

'null' was undefined because I had not included xs1.h.

'null' can be passed to a function with nullable types.