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simon
Joined: 05 Jul 2006
Posts: 270
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 Posted: Thu Jan 05, 2023 11:28 pm Post subject: Character value gets lost |
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The following program may be eligible for an award for the most weird and useless nonsense, but it generates an incorrect result when compiled with /FULL_DEBUG. The program is on the long side, but I have tried hard to simplify it, and it seems that with almost any change, the problem disappears.
The program (in the first code segment) calls a subroutine s1, which is supposed to copy the value of getsLost into ctest, but ctest prints as blank. The module is broken into two halves because it is apparently too long. Subroutine s1 performs a set of apparently meaningless operations, calling functions and subroutines most of which do essentially nothing, but somehow they combine to lose the value of getsLost. All the code between lines 32 (starting immediately after the "Do nothing meaningful" comment) and 76 (immediately before the "Try to use the value of getsLost" comment) has no intentional logic - it is purely what is left after a very long process of reducing a much larger programme to a minimum. There are many obvious ways to simplify this section of the code, but not, I have found, without making the error disappear.
I have the same problem occurring without using /FULL_DEBUG, but it will be a large task to try to isolate that. I am hoping the problem can be identified using this example.
| Code: | Program p
Use m
Integer :: i1
Logical :: l1
Character(Len= 2) :: getsLost = '?'
Character(Len=64), Dimension(2) :: cs1, cs2
!
i1 = 3
t3%i1 = 1
t3%i2 = 2
t3%i3 = 3
Call s1 (getsLost, cs1, cs2, l1, i1)
Print*, ctest
End Program p
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simon
Joined: 05 Jul 2006
Posts: 270
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| Posted: Thu Jan 05, 2023 11:36 pm Post subject: |
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Module part 1:
| Code: | Module m
!
Type t
Integer :: i1
Integer :: i2
Integer :: i3
End Type t
Interface Operator(<)
Module Procedure f1
End Interface
!
Integer :: i3 = 1
Integer :: i4 = 1
Character(Len=2) :: c1, ctest
Logical :: l2
Type(t) :: t1, t2, t3
!
Contains
!
Subroutine s1 (getsLost, cs1, cs2, l1, i1, &
i2, is1, is2, at)
Integer :: i1
Character(Len=*) :: getsLost
Character(Len=*), Dimension(:) :: cs1, cs2
Logical :: l1
!
Integer, Optional :: i2
Type(t), Optional :: at
Integer, Dimension(:), Optional :: is1, is2
!
! Do nothing meaningful
If (Present(i2)) Then
l2 = (i2 > 0)
Else
l2 = .false.
End If
l1 = Present(i2)
i3 = Count([l1, l2])
c1 = f2(i3, 1, i4)
c1 = f2(i3, 1, i4) ! - needs to be repeated -
l2 = (c1 == ' ')
t1%i1 = 1
t1%i2 = 1
t1%i3 = 1
t2%i1 = i1
t2%i2 = i1
t2%i3 = 1
Call s2 (i3*i4, t2)
If (i3 < i1) Then
i3 = i4
If (Present(i2)) i2 = 2
End If
i3 = t2%i1
If (Present(at)) Then
If (at%i2 < 1) Then
at%i1 = t3%i1
at%i2 = t3%i2 + at%i2
at%i3 = 1
Do
If (at%i2 < 0) Exit
at%i2 = at%i2 + 1
at%i1 = at%i1 - 1
End Do
End If
If (t2 < t1) i4 = 2
End If
Select Case (i4)
Case (1)
If (l1) Then
i4 = i1
Else
i4 = i1
End If
Case Default
i4 = i1
End Select
! Try to use the value of getsLost
ctest = f0(getsLost, i4, l2, .false.)
Return
!
Contains
!
Character(Len=256) Function f0(getsLost, i, l1, l2)
Integer :: i
Character(Len=*) :: getsLost
Logical :: l1, l2
f0 = Trim(getsLost)
End Function f0
End Subroutine s1
!
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Module part 2:
| Code: | Subroutine s2 (i, d)
Integer :: i
Type(t) :: d
Return
End Subroutine s2
!
Logical Function f1(t1, t2)
Type(t), Intent(In) :: t1, t2
f1 = .false.
End Function f1
!
Character Function f2(i1, i2, i3)
Integer :: i1, i2, i3
f2 = ' '
End Function f2
End Module m
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simon
Joined: 05 Jul 2006
Posts: 270
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| Posted: Wed Mar 01, 2023 5:39 pm Post subject: |
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| I appreciate that this example was not ideal, but I'm wondering whether Silverfrost had any thoughts about it. I am trying to construct a URL that is used to download some data, but because of the bug, part of the URL gets lost. And without having a clearer sense of what is wrong in the example, I do not know how to code a work-around. The code works perfectly ok with other compilers. |
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PaulLaidler
Site Admin
Joined: 21 Feb 2005
Posts: 8011
Location: Salford, UK
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| Posted: Thu Mar 02, 2023 8:36 am Post subject: |
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Simon
I am sorry but I missed your initial post on Jan 5th.
I will take a look at your code as soon as possible. |
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PaulLaidler
Site Admin
Joined: 21 Feb 2005
Posts: 8011
Location: Salford, UK
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| Posted: Thu Mar 02, 2023 2:45 pm Post subject: |
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Simon
As far as I can see, your code works correctly except for Win32 when using /FULL_DEBUG and no other debugging options such as /CHECK.
It can be fixed in this particular context by initialising "getslost" in a runtime assignment instead of in its declaration.
/FULL_DEBUG is like /DEBUG but it allows you to view PARAMETERs when debugging. It serves no purpose in this context because there are no PARAMETERs in the code. |
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simon
Joined: 05 Jul 2006
Posts: 270
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| Posted: Thu Mar 02, 2023 6:13 pm Post subject: |
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| Thanks Paul. I made a few changes, which seem to have fixed the problem in 8.96. I will aim to provide a better example if the problem reappears without /FULL_DEBUG |
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