gawk anomaly?

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2 total messages Started by Don Stewart Mon, 06 Apr 1992 05:55

#99

Author: Don Stewart
Date: Mon, 06 Apr 1992 05:55

26 lines
1508 bytes

In the following, the line 'print "class:"$0' prints nothing as the code now stands.
HOwever, by uncommenting 'print class[$2]', the above DOES print.
What am i doing wrong? (fails even in this stripped eg)
---------------------------------
/depot/gnu/bin/gawk ' 
 FILENAME == "rt.crse" {      # fmt of crse data: crse#[.A-H]section{\t}instructor
	      course[$1]=$2   # eg. 103.001	smith
	    }                 #     497B001	wesson
 FILENAME == "SHIELDS.data" {                    # student registration data
		      if(substr($0,52,1) != " ") # data has space if no course letter
		        crse = substr($0,49,7)   # eg. convert '103 001' -> '103.001'
		      else                         
		        crse = substr($0,49,3)"."substr($0,53,3) 
		      if (crse in course) {
			class[substr($0,22,9)] = class[substr($0,22,9)] ":" crse  
		         		#'22,9' is ssn
		      }
       }
 FILENAME == "masterssn" {
	OFS = ":"
#       print class[$2]  #bad side effect: this creates entry for $2 w/ null value
    if ($2 in class) {
     print "class:"$0
    }
 }
' FS="	" rt.crse FS=":" masterssn SHIELDS.data

Re: gawk anomaly?

#104

Author: Noah Friedman
Date: Tue, 07 Apr 1992 05:51

17 lines
1221 bytes

>In the following, the line 'print "class:"$0' prints nothing as the code now stands.
>HOwever, by uncommenting 'print class[$2]', the above DOES print.
>What am i doing wrong? (fails even in this stripped eg)

   By referencing class[$2], you are automatically creating an index in
class even if it didn't exist previously.  Thus, when you uncomment this
line you are causing the condition "if ($2 in class)" to become true.

   The reason why the print "class:"$0 doesn't get printed is that that
particular block doesn't get executed at all as the code now stands. 

>...
>#       print class[$2]  #bad side effect: this creates entry for $2 w/ null value
>    if ($2 in class) {
>     print "class:"$0
>    }
>...

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