Re: Extern/scope issue

[DLearner via Digitalmars-d-learn]

On Saturday, 3 April 2021 at 13:50:27 UTC, ag0aep6g wrote:

On 03.04.21 15:34, DLearner wrote:

The following produces the expected result.

However, changing extern(C) to extern(D) causes linker failures.

To me, that is bizarre.
Testmain:
extern(C) int xvar;

[...]

Testmod:
extern extern(C) int xvar;

With `extern (C)`, those two `xvar`s refer to the same data.

Without `extern (C)` (or with `extern (D)`), they are distinct variables with no relation to another. In D, you don't re-declare another module's symbols. You import the other module.

----
module testmain;

import std.stdio: writeln;
import testmod: testsub, xvar;

void main()
{
    xvar = 1;
    writeln(xvar); /* prints "1" */
    testsub();
    writeln(xvar); /* prints "2" */
}
----

----
module testmod;

int xvar; /* same as `extern (D) int xvar;` */

void testsub()
{
   xvar = 2;
}
----

Thank you, your suggestions worked.
No externs anywhere.
For the record, the code is below.
import itf;
import testmod:testsub;
void main() {
   import std.stdio;

   writeln("Entering: main");
   xvar = 1;
   writeln("xvar=", xvar);
   testsub();
   writeln("xvar=", xvar);

   writeln("Leaving: main");
}

module itf;
int xvar;

module testmod;
import itf;
void testsub() {

   import std.stdio;

   writeln("Entering: testsub");
   writeln("xvar=", xvar);
   xvar = 2;
   writeln("xvar=", xvar);
   writeln("Leaving: testsub");
}