Summary of Mixed-Language Issues

Mixed-language programming involves a call from a routine written in one language to a function, procedure, or subroutine written in another language. For example, a Fortran main program may need to execute a specific task that you want to program separately in an assembly-language procedure, or you may need to call an existing shared library or system procedure.

Mixed-language programming is possible with Intel® Fortran and Intel® C++ because each language implements functions, subroutines, and procedures in approximately the same way. The following table shows how different kinds of routines from each language correspond to each other. For example, a C main program could call an external void function, which is actually implemented as a Fortran subroutine:

Language Equivalents for Calls to Routines

There are some important differences in the way languages implement routines. Argument passing, naming conventions, and other interface issues must be thoughtfully and consistently reconciled between any two languages to prevent program failure and indeterminate results. However, the advantages of mixed-language programming often make the extra effort worthwhile.

A summary of a few mixed-language advantages and restrictions follows:

• Fortran/Assembly Language

  Assembly-language routines are small and execute very quickly because they do not require initialization as do high-level languages like Fortran and C. Also, they allow access to hardware instructions unavailable to the high-level language user. In a Fortran/assembly-language program, compiling the main routine in Fortran gives the assembly code access to Fortran high-level procedures and library functions, yet allows freedom to tune the assembly-language routines for maximum speed and efficiency. The main program can also be an assembly-language program.

• Fortran/C (or C++)

  Generally, Fortran/C programs are mixed to allow one to use existing code written in the other language. Either Fortran or C can call the other, so the main routine can be in either language.

This section provides an explanation of the keywords, attributes, and techniques you can use to reconcile differences between Fortran and other languages. Adjusting calling conventions, adjusting naming conventions and writing interface procedures are discussed in the next sections:

• Adjusting Calling Conventions in Mixed-Language Programming
• Adjusting Naming Conventions in Mixed-Language Programming
• Prototyping a Procedure in Fortran

After establishing a consistent interface between mixed-language procedures, you then need to reconcile any differences in the treatment of individual data types (strings, arrays, and so on). This is discussed in Exchanging and Accessing Data in Mixed-Language Programming.

Note

This section uses the term "routine" in a generic way, to refer to functions, subroutines, and procedures from different languages.