Unformatted WRITE of user-defined datatype

[michael-a-carr]

I have a gigantic array (several dozen megabytes) of a user-defined datatype. I would like to write this array out to a binary file using unformatted I/O for fastest operation.

Let's say that my array is X. This is my line of code:

TYPE(MYTYPE), ALLOCATABLE :: X
...
WRITE(3) X

However, when I execute this line I get "stack overflow." I can avoid the stack overflow by increasing the stack size, but this eventually leads to a stack size equal to the amount of system memory. I can also avoid it by writing out one element of the array at a time, but then I don't get the excellent performance of the unformatted write. Finally, I could write out the array in many smaller chunks, but this leads to a bunch of messy code.

Are there any ways to solve this problem short of increasing the stack size to a gigantic size?

Thank you,
Michael Carr

[Steven_L_Intel1]

I can't reproduce this in 6.5. I suggest you send a small but complete example to us at vf-support@compaq.com and we'll take a look.

Steve

[paulw]

Hi Michael, your problem sounds like it's the same as if you tried to write
an array in a subroutine, like this:

SUBROUTINE SUBNAM(X,Y,Z)
DIMENSION X(*)

WRITE(IUNIT)X
........

The above does not work because "WRITE" has no way to know how many
elements the array X has.

In your case also, I would ask how the WRITE statement knows how big
the "ALLOCATABLE" array is, as you did not show a line of code that
allocated the size.

I don't know what the disk format is for unformatted write in this compiler,
but I can tell you that others I have used split large volume output into
blocks anyway, like 256 bytes, starting with a block count and containing
a CRC check. I you can find out from COMPAQ what the block size is,
then writing data in blocks that match the blocksize should be just as
efficient.
Regards, Paul Dent

[Jugoslav_Dujic]

...btw, what happens when you try to WRITE into a binary file
a structure containing POINTERs to arrays or, still worse,
if it is a part of, say, linked list with POINTERs to another structures?

AFAIK, CVF stores POINTERs to arrays inside a structure in an
array descriptor. Are array elements stored somewhere in the file also
(as a naive user would expect), or, as I suspect, isn't the descriptor just
copied byte-by-byte to disk, thus losing its association with the target
when the file is reloaded on, say, a later run of the application? What the
(F2k draft) standard say should happen?

(Perhaps this belongs to another thread - but perhaps it has something
related with the problem of the original poster?)

Regards,
Jugoslav