宏调用结果分析

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%let Mv=shoes;
%macro PRODUCT(Mv=bicycles);
%let Mv=clothes;
%mend;
%PRODUCT(Mv=tents)
%put Mv is &Mv;
结果是 Mv is shoes;

%let Mv=shoes;
%macro PRODUCT(Mva=bicycles);
%let Mv=clothes;
%put aa;
%mend;
%PRODUCT(Mva=tents)
%put Mv is &Mv;
结果是Mv is clothes;

求结果分析，为何

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关键词：结果分析 Product clothes produc Cycles clothes shoes

看看

You are confused by a macro variable scope.

A local macro variable lives within its scope. See comments below.

18   %let Mv=shoes;  ***Mv has a global scope;
19   %macro PRODUCT(Mv=bicycles);***Mv has a local scope;
20   %put Mv is &Mv;
21   %mend;
22
23   %PRODUCT(Mv=tents)
Mv is tents
24   %PRODUCT(Mv=clothes)
Mv is clothes
25   %PRODUCT(Mv=cars)
Mv is cars
26
27   %put Mv is &Mv;
Mv is shoes

很明显，你把局部宏变量宏程序中的宏变量进行了混淆，建议你将宏变理的运作原理再重新看一遍ADVANCE那本书中讲得很清楚

因为开头定义了全局的宏变量Mv, 因此在%product里再次定义mv时, 将全局mv的值修改为clothes, 打印出的结果为clothes. 在%product中加%local mv; 全局mv的值仍为shoes.
%let Mv=shoes;
%macro PRODUCT;
%local mv;
%let Mv=clothes;
%mend;
%PRODUCT;
%put Mv is &Mv;

echotianxia 发表于 2011-12-7 10:00
很明显，你把局部宏变量宏程序中的宏变量进行了混淆，建议你将宏变理的运作原理再重新看一遍ADVANCE那本书中 ...

请问ADWANCE 是哪一本，全名是什么？谢谢。

I think he want to ask why he obtain the different result after inputting the different value in the marco (1st, MV=XXX global value for MV is still "shoes", 2nd. MVA=XXX the value for MV is chaged to 'clothes'). I am confused too.

OK, I got it for this one. Thanks for kittyforever, "在注册列表定义宏变量就相当与在宏程序中写%local语句."