Undefined reference to `omp_get_wtime_' error

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1

Hi Fortran experts here,

I am following source code from <>.
it has one module called toolbox with hundreds of subroutines.

I am using a cygwin system to run this code.

I am trying to run a program called prog02_02.f90
A: it uses toolbox.f90 module
B: I run gfortran -c toolbox.f90 prog02_02.f90
C: it generates: toolbox.mod, toolbox.o, prog02_02.o
D: I run: gfortran toolbox.o prog02_02.o
it give error message: undefined reference to `omp_get_wtime_’ error
see the screenshot attached.
if this error is something very common, I will appreciate if any expert can simply point out some solution to solve it.
I appreciate your time and help.

Martin

Screenshot 2022-04-27 151508
Screenshot 2022-04-27 1515081342×177 15.7 KB

2

You have to link your program against OpenMP, using the -fopenmp flag for GNU Fortran.

1 Like
3

Hi Interkosmos,

It works. much appreciate your help.

The prog02_02.f90 is as below: I do not notice any mention of openMP, sorry for my basic question, I literally know nothing about parallel computing.

program lineqsys

use toolbox

implicit none

integer :: i, j

real*8 :: A(3, 3), b(3)

real*8 :: L(3, 3), U(3, 3)

! set up matrix and vector

A(1, :) = (/ 2d0,  0d0,  1d0/)

A(2, :) = (/ 0d0,  4d0,  1d0/)

A(3, :) = (/ 1d0,  1d0,  2d0/)

b       = (/30d0, 40d0, 30d0/)

! solve the system

call lu_solve(A, b)

! decompose matrix

call lu_dec(A, L, U)

! output

write(*,'(a,3f7.2/)')'    x = ', (b(j),j=1,3)

write(*,'(a,3f7.2/,2(5x,3f7.2/))') &

    ' L = ',((L(i,j),j=1,3),i=1,3)

write(*,'(a,3f7.2/,2(5x,3f7.2/))') &

    ' U = ',((U(i,j),j=1,3),i=1,3)

end program

Regards

Martin

4

The main program may not contain any OpenMP calls or directives, but one or more routines in the “toolbox” may. Look for an invocation of omp_get_wtime() in those routines, and verify that such an invocation is within !$omp directives and that the toolbox gets compiled with -fopenmp.

5

Hi Mecej4,

No mention of !$omp in the two subroutines called in the prog02_02. but I find
omp is mentioned in one toc subroutine with the line: time = omp_get_wtime()
which is exactly what the error message is about. but since it is not called by prog02_02, it is strange that it triggered the error message.

anyway, really appreciate your time and help

Martin

subroutine toc(file)

    use omp_lib  
        

    ! optional file identifier

    integer, intent(in), optional :: file        

    real*8 :: time

    integer :: outfile

    real*8 :: times(4)
   

    ! get cpu time

    time = omp_get_wtime()
  

    ! calculate time difference

    time = time - starttime_cpu
   
    ! get number of days

    times(1) = floor(time/(24d0*60d0*60d0))

    time = time - times(1)*24d0*60d0*60d0
 

    ! get number of hours

    times(2) = floor(time/(60d0*60d0))

    time = time - times(2)*60d0*60d0
  

    ! get number of minutes

    times(3) = floor(time/60d0)

    time = time - times(3)*60d0

    ! get number of seconds

    times(4) = time

    call outTime(times, outfile)

end subroutine toc
6

That statement is based on a misconception. Your program may itself contain no calls to the missing routine, and during a run the statement in the “toolbox” routine that contains the call to omp_get_wtime() may never be executed, but a linker may not care about that. Some linkers may work a bit harder to find out which listed external references are not needed, and avoid linking in those external references, and may do so only if requested with an appropriate flag.

7

you are right. since I am process the whole of toolbox module, not just the two subroutines.

thanks

Martin