CODEWITHSUNDEEP
compiler-errorsfortranfortran90gfortran
mod0
mod0

Reputation: 155

Modules and legacy Fortran 77 codes

I have set of blas/lapack functions that I got from NETLIB website. I would like to put these functions inside a Fortran module. The rest of my code is in Fortran 90. So I go about doing this:

module modname
contains


double precision function ddot(n,dx,incx,dy,incy)
.
.
.
end function 


subroutine dpofa(a,lda,n,info) 
.
.
        double precision ddot
.
end subroutine dopfa
end module

When I compile using

gfortran modname.f90

I get the following error:

/tmp/ccC2EUFj.o: In function __temp_MOD_dpofa': temp.f90:(.text+0x11c): undefined reference toddot_'

I am ignoring the error about Undefined reference to main, I realize it happens because I do not have program .. end program statements in the file.

If, however, I remove the lines with module modname, contains and end module the compiler compiles without any issues.

What could possibly be the issue?

Upvotes: 2

Views: 888

Answers (1)

francescalus
francescalus

Reputation: 32366

In your non-module approach you have lots of external functions and subroutines. That is, if these are defined outside the module then one procedure has no clue about another. You tell the subroutine dpofa about the function ddot by using the declaration statement double precision ddot. The compiler mangles that name to ddot_ (see elsewhere for details of that) and also mangles the name of the real function you have to the same. The linker resolves one symbol to the other when needed.

When you come to using a module, you still have this external function declaration, but now the real function you have, in the same module, is no longer external. Instead, there is a module procedure which gets mangled to something like __temp_MOD_ddot. You aren't creating a function with the mangled name ddot_ any longer.

You presumably have a reference to the function ddot in dpofa, but in the module version that will be to the symbol ddot_ which isn't defined.

You'll want to remove the function declarations for those functions which are now defined in the same module, and are no longer external.

Upvotes: 3

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