Unexpected data declaration error in Fortran when creating array

Question

I've written a simple test program to demonstrate a data declaration error that I am receiving when compiling some Fortran code. The compile error occurs on a line where I am trying to create an array of arbitrary size. In C code, I believe that this would be accomplished with a simple `malloc`, but this type of methodology may not be useful in Fortran. What is going wrong here, and how might I fix it? I am using the `gfortran` compiler on `GNU/Linux`, so I think that it would be possible to use all of the supported language features. Here is my test program: ``` program test implicit none integer num1, num2 print *, 'Starting...' num1 = 10 num2 = 11 call sub(num1, num2) print *, 'Done.' end program subroutine sub(num1, num2) integer num1, num2 integer num3 num3 = num1 + num2 - 1 integer A(num3) do i = 1,num3 A(i) = i end do print *, 'Now printing out vector' do i = 1,num3 print *, A(i) end do end subroutine ``` Here is the `cmake` script being used to compile my simple test program:…

Accepted Answer

The problem is, because you placed a data declaration statement after a normal statement.

You do not have to use user defined dynamic allocation, the so called automatic allocation is enough. (It works also in C99 AFAIK, but only for stack allocations). Just replace

```
num3 = num1 + num2 - 1
integer A(num3)
```

with

```
integer A(num1 + num2 - 1)
integer num3

num3 = num1 + num2 - 1
```

.

Unfortunately, you cannot just write

```
integer :: num3 = num1 + num2 - 1
```

because the variable would be implicitly `SAVE` and num1 and num2 would have to be known at compile time.

Note I didn't check for other errors.

As a completely different issue I recommend you to use mudules for all your subroutines. In this simple case also an internal subroutine one would do. You have an explicit interface then and you can check for consistency of your calls and use more advanced features.

Unexpected data declaration error in Fortran when creating array

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