PRB: F6700 Heap Space Exceeded

ID: Q125468

The information in this article applies to:

Microsoft FORTRAN Compiler for MS-DOS, version 5.1

SYMPTOMS

When you run a QuickWin program and try to allocate a huge array dynamically, the return code may be 6700. The associated error message, as documented in the FORTRAN Professional Development System on page 489, is:

F6700 heap space limit exceeded

CAUSE

One cause of the error may be attempting to allocate a huge array (greater than 64K) where the data items do not align on 64K segment boundaries.

RESOLUTION

Change the data type such that the array will align on the 64K boundary.

STATUS

This behavior is by design.

MORE INFORMATION

If you attempt to dimension the huge array statically, the compiler produces this error:

F2120 : <array name>: huge array cannot be aligned to segment boundary

Compiling and running the following code sample produces an output for 'istat' of 6700, indicating the heap space was exceeded and no dynamic memory was allocated.

If you change the line declaring the array 'str' as allocatable into a comment, and change the static declaration from a comment into an excuted line, the compiler produces the F2120 error.

Changing the declaration to:


   CHARACTER*16 str(10, 6400)

eliminates the error in both cases.

Sample Code


/* Compile options needed: /MW
*/ 
      PROGRAM testmem

C     QuickWin application so we can use more than 640K
C
C     Create an allocatable array over 64K
      CHARACTER*12 str[ALLOCATABLE, HUGE](:,:)
C     Creating the array statically produces the F2120 error

C      CHARACTER*12 str(10, 6400)

      INTEGER istat
C     The allocate should fail with error 2120
C     since a single string crosses a segment boundary
C     but instead produces an error 6700
C     indicating heap space limit exceeded
      ALLOCATE(str(10, 6400), stat=istat)
      PRINT*, "Error code (0 is success) = ", istat
      IF(istat .eq. 0) THEN
           DEALLOCATE(str)
      END IF
      END

Additional query words: 5.10 fail memory allocation

Keywords :
Version : :5.1
Platform :
Issue type :