FIX: Error Message When Comparing Large Strings

ID: Q114465

The information in this article applies to:

Microsoft Visual FoxPro for Windows, version 3.0
Microsoft FoxPro for Windows, versions 2.5a, 2.5b, 2.6x
Microsoft FoxPro for MS-DOS, versions 2.5a, 2.5b, 2.6x
Microsoft FoxPro for Macintosh, version 2.6a

SYMPTOMS

In FoxPro for Windows or FoxPro for MS-DOS, when you try to compare two very large string variables while a nonmachine collating sequence is in effect, FoxPro generates an "insufficient stack space" error message.

In FoxPro for Macintosh on a 68K Macintosh, FoxPro may give the following error when comparing two character strings if there is a CODEPAGE=AUTO line in the FoxPro configuration file and a collation sequence other than Machine:

The application "unknown" has unexpectedly quit because an error of type 28 occurred.

In FoxPro for Macintosh on a PowerPC Macintosh, FoxPro may produce an Internal Consistency Error. The PowerPC may not produce an error initially. Reissuing the SET COLLATE TO 'general' command has been reported to cause a Type 11 error. In short, the error message and results on a PowerPC may be inconsistent.

CAUSE

These problems occur because FoxPro builds a key for the left and right sides of the equation. To ensure that the result will work in all languages (English, French, Spanish, and so on), FoxPro asks for a stack that is four times as long as the string being made into a key.

This behavior makes sense if you understand how international keys are constructed -- there could be a diacritical mark (accent) on each character in the string, and some characters could be expansions where a single character represents two characters. For example, the German beta character represents ss. For these reasons, FoxPro asks for 2*2*n bytes.

With a large string such as an entire memo field, FoxPro may ask for more stack space than is available. The problems listed in the Symptoms section of this article may occur when one of the strings is around 10,000 characters.

STATUS

Microsoft has confirmed this to be a problem in the Microsoft products listed at the beginning of this article. This problem was corrected in Visual FoxPro 3.0b for Windows.

MORE INFORMATION

Steps to Reproduce Problem

Type "CODEPAGE=AUTO" (without the quotation marks) in the configuration file.

Start FoxPro.

Create a program named TEST, and give it the following content: PARAMETER sequence, strlen SET TALK OFF SET COLLATE TO sequence a=REPLICATE('X',strlen) b='Z' ?a=b

This program creates two memory variables of type character. Then it compares the two variables. You pass the desired collation sequence to the parameter sequence. The problem occurs with all collation sequences except "machine." The following examples all use the 'general' collation sequence for illustration purposes only. You will pass the desired string length for "a" to the parameter, strlen.

NOTE: The values for strlen provided here cause the problem in each version of FoxPro, as noted. However, these values may vary. To produce the error, you may want to increase the second parameter that you pass to the above code. The REPLICATE command is being used to create long character strings for comparison. You will pass the desired string length for "a" to the parameter, strlen.

In FoxPro version 2.5a or 2.5b for Windows, this worked:


   DO test WITH 'general',8926

But changing the value of strlen to 8927 produced a general protection (GP) fault, and FoxPro remained in memory. You could use a memory monitor to see that User memory and physical memory are reduced after loading FoxPro. After the GP fault, memory is not recovered, so you must restart Windows.

In the 16-bit version of FoxPro version 2.5a or 2.5b for MS-DOS, this worked:


   DO test WITH 'general', 3899

But changing the value of strlen to 3900 produced an "Internal consistency error." Changing the value of strlen to 8925 caused the computer to reboot. Changing the value of strlen to 8926 caused the computer to hang (stop responding). In this situation the computer could not be warm-booted. It required a cold or hard boot.

In the 32-bit version of FoxPro version 2.5a or 2.5b for MS-DOS, this worked:


   DO test WITH 'general',8776

But changing the value of strlen to 8777 causes FoxPro to display what appears to be a corrupted alert window with the "Internal consistency error" message. Increasing the value of strlen can also result in an "abnormal termination. Page fault" error message.

In FoxPro version 2.5b for Macintosh, this worked:


   DO test WITH 'general',9912

But changing the value of strlen to 9913 produced this alert:

The application "unknown" has unexpectedly quit because an error of type 28 occurred.

In FoxPro version 2.6 for Windows, this worked: DO test WITH 'general',8927
But changing the value of strlen to 8928 caused an "Insufficient stack space" error.

In the 16-bit version of FoxPro version 2.6 for MS-DOS, this worked: DO test WITH 'general',3898
But changing the value of strlen to 3899 produced an "Internal consistency error" message. In the 32-bit version of FoxPro version 2.6 for MS-DOS, this worked: DO test WITH 'general',8774
But changing the value of strlen to 8775 displayed what appears to be a corrupted alert window with the "Internal consistency error" message. Increasing the value of strlen to 8790 produced an "Insufficient stack space" error message.

In Visual FoxPro, this worked: DO test WITH 'general',8929
But changing the value of strlen to 8930 caused an "Insufficient stack space" error.

Additional query words: VFoxWin FoxWin FoxMac FoxDos 2.60 buglist2.50a buglist2.50b buglist2.60 buglist2.60a fixlist3.00b buglist3.00 err msg errmsg GPF ICE crash non-machine hung frozen

Keywords : kberrmsg FxprgGeneral
Version : 2.50a 2.50b 2.60 2.60a 3.00 | 2.
Platform : MACINTOSH MS-DOS WINDOWS
Issue type :