Q105932: FIX: String Concatenation May Cause Memory Errors

Article: Q105932
Product(s): Microsoft Fortran Compiler
Version(s): 1.0,1.0a
Operating System(s): 
Keyword(s): 
Last Modified: 24-MAR-2000

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The information in this article applies to:

- Microsoft FORTRAN PowerStation for MS-DOS, versions 1.0, 1.0a 
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SYMPTOMS
========

Character string concatenations that involve the automatic creation of temporary
variables may cause the following memory related run-time problems:

- Very slow execution of the application

- F6700

- DX2010

RESOLUTION
==========

This memory loss can be avoided by assigning the concatenated strings to a
temporary character string variable.

STATUS
======

Microsoft has confirmed this to be a problem in FORTRAN PowerStation version
1.0. This problem has been resolved with FORTRAN PowerStation maintenance
release version 1.0a for MS-DOS.

FORTRAN PowerStation version 1.0 can be differentiated from the maintenance
release version 1.0a by invoking the linker. Typing "link32 | more" from
\F32\BIN directory will show version 2.8 for FORTRAN PowerStation version 1.0,
and it will show version 1.0f for the maintenance release version 1.0a.

MORE INFORMATION
================

The following two sample programs demonstrate a memory loss due to string
concatenation in the argument list. In both of the following examples, using a
temporary variable for the concatenated strings avoids the memory leak.

Sample Code 1
-------------

  C Compile options needed: none
        character*40 c1,c2
        c1 = 'abcd'
        c2 = 'efgh'
        k = 0
        do i=1,500000
          if(c1//c2 .eq. 'Never') k = k + 1
        end do
        end

The code above will run very slowly, and eventually generate:

  run-time error F6700
  - heap space limit exceeded

Sample Code 2
-------------

  C Compile options needed: none
        character fmtout*20,label(1,3)*(9)
        double precision value
        data (label(1,j),j=1,3)/' Label',' Output',' Test'/ 
        data value/3.14159/ 
        fmtout='f10.3'
        write(6,'(3a,''='','//fmtout//')')(label(1,j),j=1,3),value
        end

The above code on execution will generate:

  DOSXMSF : error DX2010: invalid pointer passed to free or realloc :
  0005F0F8h.
  DOSXMSF : error DX2010: invalid pointer passed to free or realloc :
  0005F0F8h.
  Label Output Test = 3.142

The code does run to completion because this type of DOS-extender error is not
fatal.

Additional query words: 1.00 buglist1.00 fixlist1.00a

======================================================================
Keywords          :  
Technology        : kbAudDeveloper kbFortranSearch kbZNotKeyword3 kbFORTRANPower100DOS kbFORTRANPower100aDOS
Version           : :1.0,1.0a
Issue type        : kbbug
Solution Type     : kbfix

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