Use Standard Fortran Interoperability Syntax for Existing Fortran...

Intel® Fortran Compiler Classic and Intel® Fortran Compiler Developer Guide and Reference

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ID 767251

Date 6/24/2024

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Use Standard Fortran Interoperability Syntax for Existing Fortran Extensions

Before the introduction of the Standard Fortran interoperability features, extensions provided by Intel® Fortran were used to facilitate programming using code written in Fortran and C. The Fortran 2003 standard defined new language features for C interoperability; in many cases, these features can be used instead of existing Intel® Fortran extensions.

The following table lists the legacy Intel® Fortran extensions and shows their Standard Fortran equivalents. This color indicates an Intel extension (non-standard feature) that may or may not be implemented by other compilers.

NOTE:

Existing code using legacy extensions will continue to work; however, if you are writing new code, you should use the standard syntax.

Legacy Extension	Standard Fortran Interoperability Equivalent
ATTRIBUTES ALIAS	Use BIND(C,NAME=<alias-name>). The BIND(C) syntax also implies ATTRIBUTES DECORATE; the compiler applies whatever name decoration (leading or trailing underscores) that C would use for the name. If the NAME= keyword is omitted, Intel® Fortran will use the Fortran name converted to lowercase on all platforms. If the procedure has no arguments, you must indicate that with () when adding BIND. All arguments to a routine specified as interoperable (with BIND(C)) must themselves be interoperable. You can also specify BIND(C) on module variables and COMMON blocks.
ATTRIBUTES C	Use BIND(C) (see ALIAS above), which has a similar effect to ATTRIBUTES C except that it does not change the argument passing mechanism to be by-value. Use the Fortran standard VALUE attribute if you need to pass by value. BIND(C) specifies that small records are passed and returned as function value results in the same way that C would. The results may be different from the Intel® Fortran default. Like ATTRIBUTES C, BIND(C) lowercases the external name and adds any necessary name decoration.
ATTRIBUTES DECORATE	Typically used with ATTRIBUTES ALIAS. See ATTRIBUTES ALIAS above.
ATTRIBUTES DEFAULT	Not needed when using BIND(C); the compiler always uses the semantics of the C compiler regardless of the setting of command-line options such as iface.
ATTRIBUTES EXTERN	Use BIND(C) with a module variable.
ATTRIBUTES REFERENCE	Not needed when using BIND(C). Typically used with character arguments, or to override the implicit pass-by-value of ATTRIBUTES C.
ATTRIBUTES STDCALL	No equivalent.
ATTRIBUTES VALUE	Use the Fortran-standard VALUE attribute. VALUE has an additional effect when used with a Fortran procedure. The dummy argument is received by value, then copied to a temporary variable that can be modified within the procedure. Once the procedure exits, the temporary value is discarded.
ATTRIBUTES VARYING	No equivalent.
%LOC function	Use the C_LOC function from intrinsic module ISO_C_BINDING, which may be an appropriate substitute for variables. C_FUNLOC is the corresponding function for procedures.
%VAL function	Declare the argument with the VALUE attribute.
%REF function	No equivalent; %REF function is the default when BIND(C) is used.

Parent topic: Mixed-Language Programming

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Intel® Fortran Compiler Classic and Intel® Fortran Compiler Developer Guide and Reference

Use Standard Fortran Interoperability Syntax for Existing Fortran Extensions