Using different variants of module in routines shared between two programs

Question

in two directories I have two different, independent Fortran 90 programs, and I want them to share certain routines that use some variables defined in modules. In other words, I have a directory dirA with program prgA.f90 and a couple of routines in an extra file sub.f90, and these routines use some stuff from a module in the file modA; all of them reside in dirA. In another directory, dirB, I have the independent code prgB.f90 that is supposed to use routines from sub.f90 and hence needs modules that define the stuff needed by it. For technical reasons, I cannot use the modules from modA in dirA directly, but write a variant of it, modB, with the same module name and containing the variables of interest with the same names as in modA as well as other variables only used by prgB. Will the routines from sub.f90 work with modA in the executable of prgA and with modB in the executable of prgB? I have partly tried to adapt my codes to this, and the compiler seems to accept it somehow, but I'm not sure if it will really work and not produce garbage results in spite of compiling seemingly ok.

Basically the question is this: Can I share functions USEing certain modules between different programs if I ensure that the modules have the same name and have a subset of variables in common, or do the modules USEd by the functions have to be exactly the same for both programs?

Thomas

Answer 1

If I understand correctly then what you are doing is just fine.

When you build progA the compiler encounters, on tackling sub.f90, a statement such as use globals. At that point the compiler will look for a file called globals.mod which it should, by that point, have created by compiling the module source. Of course, that module source need not be in a file called globals.f90 but that's neither here nor there. The module source might, for example, be in a file called globals_for_a.f90.

When you build progB the compiler encounters, on tackling sub.f90, a statement such as use globals. At that point the compiler will look for a file called globals.mod which it should, by that point, have created by compiling the module source. Of course, that module source need not be in a file called globals.f90 but that's neither here nor there. The module source might, for example, be in a file called globals_for_b.f90.

So long as the compilation for each program finds the right source for globals.mod everything should compile as you wish. You've chosen to divide your source files across a number of directories but that's not strictly necessary; a make file with suitably defined targets could build either program or both however you organise the source files and directories.

Note that almost all of this is outside the concern of the Fortran standards, it's more a question of how compilers and compilation work.