请教%symdel的用法

shiyiming

先看下面这段程序：
%let age=30;
%put &age;

%macro liu(var);
  %symdel &var;
%mend;%liu(age);

%put &age;

目的是这样的，要删除已经存在的宏变量，之所以使用宏是为了批量删除方便；
在此仅以一个宏变量age为例，但是运行后报错：
ERROR: Macro variable name & must start with a letter or underscore.

觉得问题出在%symdel这个语句对宏变量的解析上，试过多种方法包括改写做%symdel "&var";
变量倒是解析了，但同样报错：
ERROR: Macro variable name "AGE" must start with a letter or underscore.

TX们帮忙剖析下吧，在此先谢过了！

shiyiming

删除宏变量的时候，就不要再用&了

shiyiming

谢谢TX！单独删除一个宏变量时直接写名字就可以了，但是上面的问题是把%symdel放到一个宏程序里时出现的问题。

shiyiming

[code:8yuohn84]%let age=30;
%put &age;
%macro liu(var);
        %if  %symexist(&var) %then%do;
                %put Before 1: macro variable "&var"  exists;
                %symdel &var;
                %if  ^%symexist(&var) %then %put After: macro variable "&var"  deleted;
        %end;
        %else %put Before 2: macro variable "&var"  not exist;
%mend;

%liu(age)
;
%put &age; %*won't be resolved;[/code:8yuohn84]

I cannot replicate exactly the same error message as yours, but I don't see any mistakes from your original code.
On the other hand, I guess, that error could be due to an earlier-than-expected resolved macro varible.
[quote:8yuohn84]ERROR: Macro variable name & must start with a letter or underscore.[/quote:8yuohn84]
I guess that was from %symdel & var; %*unnecessary blank space between;

[quote:8yuohn84]%symdel "&var";
ERROR: Macro variable name "AGE" must start with a letter or underscore.[/quote:8yuohn84]
This is clear here %symdel "&var"--->%symdel "Age" ---> incorrect nomination for a macro variable.

*****JingJu*****

shiyiming

Thank you! But there is a WARNING: Apparent invocation of macro SYMEXIST not resolved.
I thought the reason may be the version. My system was 8.2.