Fortran 90 - "Segmentation fault - invalid memory reference" with scalable 3D array

arrays, fortran, fortran90, gfortran, segmentation-fault

Solution

The checks which many compilers have can assist you in debugging. For example with gfortran:

gfortran -g -fcheck=all -Wall segf.f90
segf.f90:5.17:

  INTEGER :: i, j, k
                 1
Warning: Unused variable 'j' declared at (1)
~/f/testy/stackoverflow> ./a.out 
At line 50 of file segf.f90
Fortran runtime error: Index '199' of dimension 3 of array 'phantom' outside of expected range (1:198)

Other compilers have similar options.

Your loops runs on such values of `l` that you are accessing the array`phantom` out of bounds.

Make sure `l` has the correct values, `1:m`, or that the dimensions of the array phantom are specified correctly to be this range (`1:m`).

Problem

I have compiled a fortran 90 program with gfortran which builds a scalable 3D array in a way I want. Upon running, I get the following error: ``` Program received signal SIGSEGV: Segmentation fault - invalid memory reference. Backtrace for this error: #0 0x10542ee42 #1 0x10542f60e #2 0x7fff8d7895a9 #3 0x10542575e #4 0x105425975 #5 0x105425d0e Segmentation fault: 11 ``` I believe this is a memory issue with the large 3D array, as it works if I decrease the dimensions, but is there anyway to get around this? Here is my code: ``` PROGRAM phantomtest IMPLICIT NONE INTEGER, PARAMETER:: columns=34, rows=34, diags=((4*columns)-6), m=(4*columns)-6+(2*columns) REAL, ALLOCATABLE, DIMENSION(:,:,:)::phantom INTEGER :: i, j, k CHARACTER (LEN=3) :: nstring, nullstring='' ALLOCATE(phantom(columns,rows,m)) phantom=0 CALL Phantom_Making(phantom,columns,rows,diags,m) WRITE(nstring,FMT="(I3)"), columns PRINT*, nullstring DO k=1,m DO i=1,columns WRITE(*,FMT="("//nstring//"I2)") phantom(i,:,k) END DO PRINT *, nullstring END DO END PROGRAM phantomtest !--------------------------- SUBROUTINE Phantom_Making(phantom,columns,rows,diags,m) IMPLICIT NONE INTEGER, INTENT(IN):: columns, rows, diags, m REAL, DIMENSION(columns,rows,m), INTENT(INOUT) :: phantom INTEGER :: i, j, k, l !Vertical and horizontal rays DO i=1,rows phantom(:,i,i) = 1 phantom(i,:,i+(columns)+(diags/2)) = 1 END DO !Diagonal rays phantom(1,2,1+columns) = 1 phantom(2,1,1+columns) = 1 phantom(1,columns-1,1+columns+(diags/2)+rows) = 1 phantom(2,columns,1+columns+(diags/2)+rows) = 1 j = columns-1 DO k=2+columns, (diags/2)+columns phantom(2:columns,:,k) = phantom(1:(columns-1),:,k-1) IF (((k+1)-columns).LE.columns) phantom(1,k+1-columns,k)=1 END DO DO l=columns+(diags/2)+rows+2, columns+(diags/2)+rows+1+(diags/2) j = j-1 phantom(2:columns,:,l) = phantom(1:(columns-1),:,l-1) IF (j.GT.0) phantom(1,j,l) = 1 END DO END SUBROUTINE ```

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