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<a name="Further-Interoperability-of-Fortran-with-C"></a>
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Previous: <a href="Working-with-Pointers.html#Working-with-Pointers" accesskey="p" rel="prev">Working with Pointers</a>, Up: <a href="Interoperability-with-C.html#Interoperability-with-C" accesskey="u" rel="up">Interoperability with C</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<a name="Further-Interoperability-of-Fortran-with-C-1"></a>
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<h4 class="subsection">7.1.6 Further Interoperability of Fortran with C</h4>
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<p>The Technical Specification ISO/IEC TS 29113:2012 on further
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interoperability of Fortran with C extends the interoperability support
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of Fortran 2003 and Fortran 2008. Besides removing some restrictions
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and constraints, it adds assumed-type (<code>TYPE(*)</code>) and assumed-rank
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(<code>dimension</code>) variables and allows for interoperability of
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assumed-shape, assumed-rank and deferred-shape arrays, including
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allocatables and pointers.
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</p>
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<p>Note: Currently, GNU Fortran does not support the array descriptor
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(dope vector) as specified in the Technical Specification, but uses
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an array descriptor with different fields. The Chasm Language
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Interoperability Tools, <a href="http://chasm-interop.sourceforge.net/">http://chasm-interop.sourceforge.net/</a>,
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provide an interface to GNU Fortran’s array descriptor.
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</p>
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<p>The Technical Specification adds the following new features, which
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are supported by GNU Fortran:
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</p>
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<ul>
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<li> The <code>ASYNCHRONOUS</code> attribute has been clarified and
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extended to allow its use with asynchronous communication in
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user-provided libraries such as in implementations of the
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Message Passing Interface specification.
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</li><li> Many constraints have been relaxed, in particular for
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the <code>C_LOC</code> and <code>C_F_POINTER</code> intrinsics.
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</li><li> The <code>OPTIONAL</code> attribute is now allowed for dummy
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arguments; an absent argument matches a <code>NULL</code> pointer.
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</li><li> Assumed types (<code>TYPE(*)</code>) have been added, which may
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only be used for dummy arguments. They are unlimited polymorphic
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but contrary to <code>CLASS(*)</code> they do not contain any type
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information, similar to C’s <code>void *</code> pointers. Expressions
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of any type and kind can be passed; thus, it can be used as
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replacement for <code>TYPE(C_PTR)</code>, avoiding the use of
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<code>C_LOC</code> in the caller.
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<p>Note, however, that <code>TYPE(*)</code> only accepts scalar arguments,
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unless the <code>DIMENSION</code> is explicitly specified. As
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<code>DIMENSION(*)</code> only supports array (including array elements) but
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no scalars, it is not a full replacement for <code>C_LOC</code>. On the
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other hand, assumed-type assumed-rank dummy arguments
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(<code>TYPE(*), DIMENSION(..)</code>) allow for both scalars and arrays, but
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require special code on the callee side to handle the array descriptor.
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</p>
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</li><li> Assumed-rank arrays (<code>DIMENSION(..)</code>) as dummy argument
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allow that scalars and arrays of any rank can be passed as actual
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argument. As the Technical Specification does not provide for direct
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means to operate with them, they have to be used either from the C side
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or be converted using <code>C_LOC</code> and <code>C_F_POINTER</code> to scalars
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or arrays of a specific rank. The rank can be determined using the
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<code>RANK</code> intrinisic.
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</li></ul>
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<p>Currently unimplemented:
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</p>
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<ul>
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<li> GNU Fortran always uses an array descriptor, which does not
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match the one of the Technical Specification. The
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<code>ISO_Fortran_binding.h</code> header file and the C functions it
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specifies are not available.
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</li><li> Using assumed-shape, assumed-rank and deferred-shape arrays in
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<code>BIND(C)</code> procedures is not fully supported. In particular,
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C interoperable strings of other length than one are not supported
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as this requires the new array descriptor.
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</li></ul>
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<hr>
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<div class="header">
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<p>
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Previous: <a href="Working-with-Pointers.html#Working-with-Pointers" accesskey="p" rel="prev">Working with Pointers</a>, Up: <a href="Interoperability-with-C.html#Interoperability-with-C" accesskey="u" rel="up">Interoperability with C</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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