carol1222 发表于 2012-3-31 17:05 
我知道了。
data _null_;
set control2 nobs=t;
This will be better, because nobs information is available in compiling time. The symputx will convert data and trim blanks automatically.
data _null_;
call symputx("m",t);
set control2 nobs=t;
stop;
run;