var_extern

[PBaswat]

Hi,
in our structure text code we have one variable declaration block known as, var_extern whose behaviour is same as var_global.
since at lot of places in our structure text project specially in programs, are using var_extern block, so is there any way inside source code of rusty we can enable support for this variable declaration block?

Note : i have attached sample programs, in which both programs inProgram.st & outProgram.st shares extern/global variable
called gnExternalIf.

------------------------------------------------------------------inProgram.st----------------------------------------------------------------
program inProgram

var_extern
	gnExternalIf : dint; (* defaults to zero *)
end_var

var
fb1 : function_block1; (checks persistence)
fb2 : function_block2; (Plays around with var_in_out and var_const)
printstr : PRINT_STRING;
asign1 : dint ;
asign2 : dint ;
asign3 : dint ;
end_var

if gnExternalIf = 0 then
asign1 := gnExternalIf + 1;
asign2 := gnExternalIf + 2;
asign3 := gnExternalIf + 3;
fb1();
elsif gnExternalIf = 1 then
fb1(I2 := asign1);
else
asign2 := gnExternalIf + 2;
asign3 := gnExternalIf + 3;
fb1();
end_if;
fb2(IO2 := asign2,
IO1 := asign3
);
printstr(CI := TRUE,
PRINTER := fb1.Q2,
IN := 'value of fb1.Q2');
printstr(CI := TRUE,
PRINTER := fb2.IO1,
IN := 'value of fb2.IO1');
printstr(CI := TRUE,
PRINTER := fb2.IO2,
IN := 'value of fb2.IO2');
printstr(CI := TRUE,
PRINTER := fb2.Q3,
IN := 'value of fb2.Q3');
printstr(CI := TRUE,
PRINTER := fb2.Q4,
IN := 'value of fb2.Q4');
printstr(CI := TRUE,
PRINTER := gnExternalIf,
IN := 'In inProgram(), gnExternalIf ');
gnExternalIf := gnExternalIf + 1;
end_program

----------------------------------------------------------------outProgram.st----------------------------------------------------------------
program outProgram
var_extern
gnExternalIf : dint; (* defaults to zero *)
end_var

var
prtString : PRINT_STRING; (* prints to the Controller panel of the emulator *)
passCount : bool := false;
end_var

if
gnExternalIf = 5
then
prtString (CI := TRUE, PRINTER := 9, IN := 'Pass');
elsif
gnExternalIf = 6
then
prtString (CI := TRUE, PRINTER := 1, IN := 'Another Pass');
passCount := true;
else
prtString (CI := TRUE, PRINTER := 2, IN := 'FAIL');
end_if;

if
passCount = true
then
case gnExternalIf of
0:
prtString (CI := TRUE, PRINTER := 3, IN := 'case 0');
1:
prtString (CI := TRUE, PRINTER := 4, IN := 'case 1');
else
prtString (CI := TRUE, PRINTER := 5, IN := 'case default');
end_case;
else
prtString (CI := TRUE, PRINTER := 6, IN := 'passCount FAIL');
end_if;

prtString(CI := TRUE,
PRINTER := gnExternalIf,
IN := 'In outProgram(), gnExternalIf ');
gnExternalIf := gnExternalIf + 1;

end_program

[TheColonel2688]

Var_extern is a really bad practice, and should have never been added to the language.

[PBaswat]

i do not have any idea on structure text, but we are using it in our programs. so how to support this var declaration block in rusty?

[ghaith]

The way the norm defines VAR_EXTERNAL is that these are global variables already defined in the application. And you explicitly state your intent of using them in a program. Any global variable not declared in your POU as a VAR_EXTERNAL is actually not visible. We chose not to implement this as in Codesys and our current systems all Global variables are always visible.
I think for norm completion we will eventually allow a VAR_EXTERNAL block but it will initially not do anything and eventually maybe we offer a strict norm mode to support it.
That being said, a VAR_EXTERNAL block that declares the global variables itself is IMHO not a good idea. You could however with rusty create global variables in any file, so moving the var_extern blocks you have to outside the program boundary and renaming them to VAR_GLOBAL would solve that issue.