Use standard features to achieve the greatest degree of portability for your Visual Fortran programs. You can design a robust implementation to improve the portability of your program, or you can choose to use extensions to the standard to increase the readability, functionality, and efficiency of your programs. You can ensure your program enforces the Fortran standard by using the /stand:f90 or /stand:f95 compiler option to flag extensions.
Not all extensions will cause problems in porting to other platforms. Many extensions are supported on a wide range of platforms, and if a system you are porting a program to supports an extension, there is no reason to avoid using it. There is no guarantee, however, that the same feature on another system will be implemented in the same way as it is in Visual Fortran. Only the Fortran standard is guaranteed to coexist uniformly on all platforms.
Compaq Fortran supports many language extensions on multiple platforms, including Compaq Alpha systems. For information on compatibility with Compaq Fortran on Alpha systems, see Compatibility with Compaq Fortran on Other Platforms. Also, the printed Compaq Fortran Language Reference Manual identifies whether each language element is supported on other Compaq Fortran platforms.
It is a good programming practice to declare any external procedures either in an EXTERNAL statement or in a procedure interface block, for the following reasons:
If you do not explicitly declare the external procedures and the name duplicates an intrinsic procedure, the processor calls the intrinsic procedure, not your external routine. For more information on how the Fortran compiler resolves name definitions, see Resolving Procedure References.