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5. Clipper programming issues

5.1 I keep getting financial arithmetic results that don't add up exactly. From time to time my calculations are off by a fewcents but I'm sure there is nothing wrong with my code. What'sthe deal?

(Excellent reply contributed by David Husnian.)

Clipper and most computer languages use a binary floating point format for their real numbers. This causes precision errors which commonly show up in calculations, comparisons and when rounding. The problem is related to trying to represent an infinite number of decimal numbers into a fixed number (and a small fixed number at that) of binary bits.

Statistically, there aren't any numbers that can be represented exactly, of course, from a practical standpoint some can be (but they are all somehow related to powers of 2, like 1/2 or 3/8 or 127/128 or ...).

Taking .275 out to just 16 bits yields:

0100011000100111 but that is really only .274993896484375. It is impossible to represent .275 accurately in a binary numbering system, even with unlimited bits, let alone the 64 bits that Clipper uses (all of which aren't used for the decimal portion).

Most modern languages use a format defined by the IEEE. An IEEE-compliant double precision implementation meets the following criteria:

In the IEEE standard, rounding is considered to be finding the closest representable number to the "exact" number. Not an easy task, particularly at the level of Clipper.

There are only two complete solutions: use only integers (for example, use 1234 to mean 12.34) or use a decimal numeric format like BCD.

With Visual Objects you will be able to make variable declarations such as LOCAL i AS INT, which will have the effect of forcing only integer values into a variable.

CA-Clipper 5.3a is compiled and linked with the 8.0 release of Microsoft C, including the standard math library component. The rounding problems under this library are likely to be somewhat less severe.

5.2 Why is "ABCDEF" = "ABC" turning up TRUE in my code?

The single equal sign operator (=) is not what you expect. If you have SET EXACT OFF (the default) then string comparisons only check as far as the length of the right-side value. If you want an exact match, then you should use the double-equals operator (==) instead. Many programmers forget about it on purpose and just SET EXACT ON, but there are times (such as looking up a partial key) when the "fuzzy match" is useful.

5.3 What is "Internal Error 667" and what can I do about it?

(Answer supplied by Josip Almasi, 10 February 1995.)

The evaluation stack (containing LOCAL variables, etc.) has crashed into a locked VM segment. Basically, the system has run out of memory as the VM system only locks segments near the evaluation stack when the memory is very old.

From Ian Day, 3 February 1995:

OK, you first have to imagine the layout of Clippers data segment (DGROUP):

         ||||||||||||          @ is where STATICs and ITEMs go
         ||||||||||||          % is where LOCALs go
         %%%%%%%%%%%%          * is the CPU stack
         ************          # is fixed C & ASM data

The rest (the '|' bit) is called 'DS available'.

As your program runs it will allocate local variables which will use up the '%' region. This regios has a high water mark and so Clipper remembers the most LOCALs that have been used at any one time (because you will most likely need that many again).

The same thing happens with STATICs & ITEMs. All statics are stuffed into the top region at startup. ITEMs (using the item API) are allocated and de-allocated by various parts of Clipper internally (as well as 3rd parties). This region also has a low water mark with the same behaviour.

If you have a lot of STATICs/ITEMs and you program tries to go deep and uses up a lot of LOCALs at the same time, the these two regions will overrun each other, and you will then get a 667, which means either the Eval Stack ('%' area) has overrun the MemVar table ('@' area) or vise versa.

So, you'd probably need to greatly reduce the number of static variables that you're using, which would most likely cure this.

If your program doesn't recurse too far, you can most likely increase your DS avail. amount by reducing your CPU stack. 4-5K should be sufficient for most things.

If you still have problems, then you might want to try our debugger (MrDebug for CA-Clipper) which has an in-built map of DGROUP and would warn you before the fault happened, and you could then see what's going on.

5.4 What is "Internal Error 1210" and what can I do about it?

(Reply supplied by Norman Mongeau.)

Internal Error 1210 occurs when the database driver discovers an index file inconsistency with which it cannot cope. There are a few things you can check in your code to eliminate this error:

5.5 What is "Internal Error 5333" and what can I do about it?

(Answer supplied by Samuel S. Shuster on 17 July 1993.)

Internal Error 5333 occurs when the virtual memory management subsystem gets overloaded and cannot find enough memory to continue execution. You can take a few steps to cope with IE 5333:

5.6 What is an "Unrecoverable Error 650: Processor Stack Fault"?

It's a result of infinite recursion, which occurs when a function calls itself, which calls itself, which calls itself, and so on without stopping. Most often this occurs when your error handler has an error, which triggers the error handler...

5.7 What is "runtime error R6003"?

The R6003 error occurs when you run a Clipper program on a machine that is 'too fast'. Part of the startup procedure in every executable is used to determine a value. That value is used in a timing loop. On very fast machines, the timing routine returns 0, causing an error in the program's initialization, since your software then fails with a divide by 0 error.

To fix this problem, there are two possibilities.

First, by the time that 5.3 was released, CA included the object that fixed the problem in that version. So, if you have 5.3, you need to link in __wait_4.obj to every executable you produce.

If you use Clipper 5.0-5.2e, there is another object, available from The Oasis. The file is named R6003FIX.ZIP, and is in the patch area. There are complete instructions included for it's use, but it is essentially the same as the 5.3 fix, just link it in on every executable you produce.

5.8 What is "internal error 8002"?

Clipper 5.3 linked with Exospace fails when creating indexes for large numbers of records and complex keys. Such a situation can result in internal error 8002. To fix this simply use OPTEDIT:

optedit myapp.exe -extramin 4096
Note that your application might require values greater than 4096.

5.9 What about the other "Internal Errors"?

An official listing of internal errors provided by Computer Associates may be found in files IE52NG.ZIP or IE52TX.ZIP, depending on whether you prefer a Norton Guide file format or a plain ASCII file. These are on the standard FTP sites, or in Library 1.

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