sas宏(2)，运行中创建宏与使用宏，多个宏触发器的引用规则、proc sql创建宏, scl中宏处理(暂缺)

1:在程序运行中进行宏定义

CALL routines that enable you to transfer information between an executing DATA step and the macro processor.

You can use the SYMPUT routine to create a macro variable and to assign to that variable any value that is available in the DATA step.  

When you use the SYMPUT routine to create a macro variable in a DATA step, the macro variable is not actually created and assigned a value until the DATA step is executed.

options symbolgen pagesize=30;  
%let crsnum=3; 
data revenue;    
set sasuser.all end=final; 
where course_number=&crsnum;     
total+1;       
if paid='Y' then paidup+1;    
if final then do;     
    if paidup<total then do;    
        call symput('foot','Some Fees Are Unpaid');     /*symput函数能达到运行时给宏赋值的效果*/
        /*%let foot=Some Fees Are Unpaid; */ /*使用let不能达到想要的效果，let会被宏处理器先执行，优先于data步*/
    end;          
    else do;      
        call symput('foot','All Students Have Paid');   
        /*%let foot=All Students Have Paid;*/  
    end;    
end;   
run;

symput函数里面的参数为表达式的情况

里面引用的函数不需要使用%这种宏函数的记号

trim去右尾 left去左尾

call symput('numpaid',trim(left(paidup))); 

CALL SYMPUTX(macro-variable, value <,symbol-table> ); 

 默认去双尾空白，其他效果和symput一样 

随后一个参数表示宏储存的位置'L'=local 'G'=global

The SYMPUT routine and the SYMPUTX routine can only create a local macro variable if a local symbol table already exists. If no local symbol table exists when the SYMPUT routine or SYMPUTX routine executes, it will create a global macro variable.

依据变量名建立宏

data _null_;
set sasuser.courses;
call symput(course_code, trim(course_title));/*每一个observation中的两个变量分别对于宏值与宏变量*/
run;
%put _user_;

多个宏触发器的扫描规则

宏处理器将两个&当做一个看待，所以第一次扫描&&&lv2被处理成&(&lv2)->&lv1,第二次扫描就得出res，先将重复的两个变成1个，然后记住扫描的位置，继续扫面后面的。

而&&lv2第一次扫描被处理成&lv2,结果依然为lv1

The Forward Re-Scan Rule

1：When multiple ampersands or percent signs precede a name token, the macroprocessor resolves two ampersands (&&) to one ampersand (&), and re-scans thereference.

2： To re-scan a reference, the macro processor scans and resolves tokens from left to right from the point where multiple ampersands or percent signs are coded, untilno more triggers can be resolved.

/*想要用lv2来得到res*/
data _null_;
%let lv1 = res;
%let lv2 = lv1;
%put &lv2; /*一个红触发器无须解释,结果为lv1*/
%put &&lv2; /*这个看上去有理，但是得出的结果还是lv1*/
%put &&&lv2;/*这个得出的结果为res*/
run;

2：在程序运行中进行宏值得获取

在程序中进行宏值得获取用&是不行的，这个是在编译前就被执行的语句。

data teachers;
set sasuser.register;
length Teacher $ 20;
teacher=symget('teach'||left(course_number));
run;

3：利用proc sql创建宏

This form of the INTO clause does not trim leading or trailing blanks

当时let创建的宏会去掉空白

/*在行数未知的情况下创建多个宏变量，*/
proc sql noprint;
    select count(*) into :numrows
        from sasuser.schedule
        where year(begin_date)=2002;
%let numrows=&numrows; /*消除首尾空白*/
%put There are &numrows courses in 2002;
    select course_code, location,
            begin_date format=mmddyy10.
        into :crsid1-:crsid&numrows,
             :place1-:place&numrows,
             :date1-:date&numrows
        from sasuser.schedule
        where year(begin_date)=2002
        order by begin_date;
%put _user_;
quit;

crsid1-crsid3 are assigned values of the data set variable Course_code from each of the first three rows，他们分别对应数据集的前三行的观测的值

如果规定的group数大于实际的数量，那么按照实际多少个来创建宏

create one macro variable that will hold all values of a certain data set variable.

proc sql noprint;
    select distinct location into :sites separated by ' '
        from sasuser.schedule;
quit;

　Global Symbol Table(符号表中，宏与宏值)
Sites Boston Dallas Seattle

Proc sql中不会进行自动的数据类型转换。对于你想要使用的数据类型要进行手动转换