Re: Data Records from Flat File (COBOL Style)

From: Bruce Wood (brucewood_at_canada.com)
Date: 03/01/05 

Date: 1 Mar 2005 12:00:17 -0800

There is a speed penalty.

The COBOL PIC clause absolutely does not have an internal length. It's
just a sequence of bytes, that the _compiler_ knows happens to be 10
long, or whatever. It does _not_ contain any attached "true length".
That is, if you declare

ABC PIC X(10)

in COBOL, there is _no way_ to indicate that you stored only 5
characters in there.

A call to Substring(5,10), or something like that, copies the ten
characters to another place in memory and adds a length (in this case,
10) to form a string object. Picking the fields out of a larger string
one-by-one involves copying each field in memory and constructing a
string for it, which costs time and memory. My point was that it
doesn't cost much in the grand scheme of things.

In more detail, here is what happens in COBOL and C# in situations like
this one.

COBOL:

ABC PIC X(10).

Any reference to "ABC" simply points to the start of the ten
characters. The compiler may or may not generate instructions to make
sure that you don't run off the end of the 10 characters, depending on
compiler switches you specify. You can manipulate the characters in
place, without copying them anywhere.

C#

string customerNumber = lineString.Substring(5, 10);

The Substring method copies ten characters from the lineString and uses
them to construct a string elsewhere in memory, with a length of 10 and
the characters copied from the lineString. A reference to that string
is then stored in customerNumber. Yes, a more intensive operation than
COBOL (which didn't need to move anything anywhere). If you're
processing a million rows you will notice a difference, but as with
many such applications most of your time will be spent doing I/O, so
even if the in-memory processing is 10x slower, it still won't make all
that much real-time difference.

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