CODEWITHSUNDEEP
fortranfortran90intel-fortran
user2820579
user2820579

Reputation: 3451

How are numeric types managed in fortran 90

I have an issue that hopefully would not affect my numerical calculations in Fortran 90.

The thing is that I have an array declared as

Real(r8), Allocatable              :: matKBody(:)

By my hand, initializing such array I done it like

allocate(matKBody(1:Nk), STAT=ierr)
If (ierr /= 0) Stop
matKBody(:) = ( 0.0_r8, 0.0_r8)

which is a way to initialize a complex array. I noticed this error but I was surprised that it doesn't matter if I initialize such array in this way or using the 'correct' statement:

matKBody(:) = 0.0_r8
... 
... ! Do some stuff with the array
...
Deallocate( matKBody, STAT=ierr )
If (ierr /= 0) Stop

If I print both arrays they give me the correct initialization , i.e. both initialize real numbers.

Why fortran (or the compiler) is not aware of such kind of things? (I used ifort for compilation).

Upvotes: 0

Views: 319

Answers (1)

M. S. B.
M. S. B.

Reputation: 29391

Full example:

program test_convert

use, intrinsic :: ISO_FORTRAN_ENV

Real(real64), Allocatable              :: matKBody(:)

allocate (matKBody (1:10) )
matKBody(:) = ( 0.0_real64, 0.0_real64)

end program test_convert

Compiled with gfortran with options: -O2 -fimplicit-none -Wall -Wline-truncation -Wcharacter-truncation -Wsurprising -Waliasing -Wimplicit-interface -Wunused-parameter -fcheck=all -std=f2008 -pedantic -fbacktrace

Output from gfortran: 

matKBody(:) = ( 0.0_real64, 0.0_real64)
              1
Warning: Possible change of value in conversion from COMPLEX(8) to REAL(8) at (1)

So some compiler are "aware" of such things and will tell you about them if you request it to.

As discussed in the comments, Fortran provides automatic conversion between types upon assignment. So this is not an error, but gfortran at least will provide a warning so that the programmer can check whether they intended the conversion. You can suppress the warning and state your intent to cause a conversion via:

matKBody(:) = real ( ( 0.0_real64, 0.0_real64), real64 )

(This is just an example, since writing = 0.0_real64 is so much simpler for this particular assignment.)

Upvotes: 1

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