Macro variables, local or not?

[CalleC]

Hi,

As a newbie, I just came across "macro variables". They are said to be local, but then I must misunderstand something. Below is an example that seems to generate a result that gives me the impression that a macro variable (in this case i) is not local within a macro, what do I miss?

%macro macro_B();
	%put macro_B ... ;	
	%do i = 1 %to 5;
		%put macro_B - looping [&=i];
	%end;
	%put macro_B - loop completed [&=i];
%mend;

%macro macro_A();
	%put macro_A ... ;	
	%do i = 1 %to 3;
		%put macro_A - looping [&=i];
		%macro_B();
	%end;
	%put macro_A - loop completed [&=i];
%mend;

%macro_A();

Yields the following output

macro_A ...
macro_A - looping [I=1]
macro_B ...
macro_B - looping [I=1]
macro_B - looping [I=2]
macro_B - looping [I=3]
macro_B - looping [I=4]
macro_B - looping [I=5]
macro_B - loop completed [I=6]
macro_A - loop completed [I=7]

Happy for a quick explanation.
//C

[WarrenKuhfeld]

https://documentation.sas.com/doc/en/mcrolref/1.0/n10i4tmalsyhgxn1hj4ud13ff074.htm

[Tom]

I suspect you do not understand what SAS means by LOCAL.

When you define a macro variable as LOCAL is means that it only exists while it is running.  If you call MACRO_B in the middle of running MACRO_A then MACRO_A  is still running so the macro variable defined in MACRO_A still exists and can be used by MACRO_B.

When the same macro variable name exists in multiple scopes (GLOBAL, MACRO_A, MACRO_B, etc.) then references will use the most local (inner most) version.

If you define a macro variable as LOCAL that will prevent your macro from modifying some existing macro variable that happened to use the same name. So making a macro variable LOCAL will make your macro play nice with others.  But it does not protect its macro variables from being modified by other macros it might call.

[Quentin · Accepted solution]

That is a lovely test case you wrote up!

The point you are missing is that macro variables defined within a macro are not (necessarily) local by default. Thus if you want a macro variable to be local (which 99.9% of the time is the right design IMHO), you need to use the %LOCAL statement to declare them to be local.  

If you add a %LOCAL statement to both macros, they will work as expected:

%macro macro_B();
	%local i ;
	%put macro_B ... ;	
	%do i = 1 %to 5;
		%put macro_B - looping [&=i];
	%end;
	%put macro_B - loop completed [&=i];
%mend;

%macro macro_A();
	%local i ;
	%put macro_A ... ;	
	%do i = 1 %to 3;
		%put macro_A - looping [&=i];
		%macro_B()
	%end;
	%put macro_A - loop completed [&=i];
%mend;

%macro_A()

Without the %local statement, your macro B will not create a local macro variable named i.  Instead the %do i=1 %to... statement in the macro B will use the macro variable i that belongs to the macro A.  And that will then cause your macro A to stop looping prematurely.  These kinds of scope collisions are a common problem if a macro does not declare the macro variables it creates to be %local. 

[CalleC]

Brilliant, many thanks all for your prompt help to improve my understanding of local macro variables 🙂