Default real kind porting problem

Question

Hi,

I've ported some Fortran code from Fortran PowerStation(4.0) to the Fortran 11(2003) compiler. In order to maintain double and real values between the old and new compiler, I changed properties>fortran>data>"Default Read Kind" from 4 to 8. Now the problem is that the global variables are not maintaining data from one file to other.

Suppose I create a real*8 variable called abc in one file as a global variable (COMMON/test/abc). It is modified in one file and used in another file. When inspecting the value of the abc variable in the second file, it is found not to contain the modified data. This happens only when I change "Default Real Kind" to 8.

Are there any other options I need to modify from the properties window?

Please give a solution. Thanks in advance.

Answer 1

Hi

I'm a bit unclear about what compiler you are using, what modifications you have made and so forth, so my answer is a bit hesitant.

I'm not sure that changing the default real kind from 4 to 8 does maintain values as you think it does. You seem to think that real(kind=4) on your old compiler means the same as real(kind=8) on your new compiler. This may be true, but it seems a bit unlikely to me.

However, don't fall into the trap of thinking that real(kind=4) must mean a 4-byte IEEE compliant floating-point number, or that real(kind=8) must mean an 8-byte IEEE fp number. This is true for most compilers, certainly for all the compilers I've used recently, but it's not required by the Fortran standard. Your old compiler may have meant something different from what your new compiler means.

Finally, I usually experience problems with common blocks when I change real number sizes in Fortran programs. The best solution is to replace common blocks with module variables. If you can't do that, check the common declarations very carefully, bearing in mind that common is an instruction to the compiler about how to lay variables out in memory. If you change the size of a variable in one declaration of the common block but not in another you will have problems.

Regards

Mark