I have a struct :

struct a {
   int i;
   // some more stuff ...
}

In a Class, I define public global void * dataSet;

In a function f, of the same class: i call :

void f() {
a[] rd_flattened;	
a[] * rd;	

// DO SOME WORK HERE ....

this.dataSet = & rd_flattened;	
rd = cast (a [] *)  dataSet;

write("length of rd is : "); writeln((*rd).length); // <--- this works..
// do some work on rd

this.dataSet = rd;
rd = cast (field.rawData [] *)  dataSet;

write("length of rd for a second time is : ");
writeln((*rd).length); // <--- this ALSO works..
}

Now outside f, in the same class, i call :

void f2() {

f();

a[] *aa ;
aa = cast (a [] *)  this.dataSet; // recall dataset is public global
// if i print the address of this.dataSet here, this is the same as inside f()
write("after calling f, count is: "); writeln((*aa).length); readln();
// here the situation completely blows up . the length is wrong.
}

I need some help here. Sorry, can't post code. It is proprietary.

What is causing this issue ?

thank you.

On Thursday, 24 June 2021 at 14:06:11 UTC, seany wrote:

// DO SOME WORK HERE ....

this.dataSet = & rd_flattened;	
rd = cast (a [] *)  dataSet;

write("length of rd is : "); writeln((*rd).length); // <--- this works..
// do some work on rd

this.dataSet = rd;
rd = cast (field.rawData [] *)  dataSet;

write("length of rd for a second time is : ");
writeln((*rd).length); // <--- this ALSO works..
}

void f2() {

f();

a[] *aa ;
aa = cast (a [] *)  this.dataSet; // recall dataset is public global
// if i print the address of this.dataSet here, this is the same as inside f()
write("after calling f, count is: "); writeln((*aa).length); readln();
// here the situation completely blows up . the length is wrong.
}

Your variable a[] rd_flattened; is a local variable to function f() allocated on the stack. Stack memory expires as soon as you return from the function. What f2() accesses through your global variable is a dangling pointer, a pointer to the expired stackframe of f(), which is why the .length is garbage.