If you are gradually building up a string by successively concatenating new values to the end of the string, you can get better performance and tidier code by building the string into a varying-length field.
Compare these two assignments using a fixed-length field and a varying-length field. If fixbuffer and varbuffer both start out with 'start value', they both end up with 'start value more data', but the assignment using fixbuffer takes much longer.
D fixbuffer s 65535a
D varbuffer s 65535a varying
fixbuffer = %trim(fixbuffer) + ' more data';
varbuffer = varbuffer + ' more data';
The operation of %TRIM requires searching from the end of the string for a non-blank character. If your variable is long, this search can take a fair amount of time when the data is short. Since the varying-length field keeps the current length of the data in the first two bytes of the variable, you don't need to do the %TRIM to locate the end of the string.
I did a little casual test where I did the following 100 times: start with an empty 65535A string and append 'a' 100 times. Using a fixed-length string, it took 40 seconds. Using a varying-length string, it took less than .01 second.
To make a more typical test, I reduced the length of the variable to 1000 and increased the length of the string being appended to 80; to get a reasonably long run, I did 100,000 iterations. Using a fixed-length string, it took 36 seconds. Using a varying-length string, it took 1 second.
Barbara Morris joined IBM in 1989 after graduating from the University of Alberta with a degree in computing science. Within IBM, she has always worked on the RPG Compiler team. You can contact Barbara at bmorris@ca.ibm.com.
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