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<title>The GNU Fortran Compiler: STRUCTURE and RECORD</title>
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<a name="STRUCTURE-and-RECORD"></a>
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<div class="header">
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<p>
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Next: <a href="UNION-and-MAP.html#UNION-and-MAP" accesskey="n" rel="next">UNION and MAP</a>, Previous: <a href="Read_002fWrite-after-EOF-marker.html#Read_002fWrite-after-EOF-marker" accesskey="p" rel="prev">Read/Write after EOF marker</a>, Up: <a href="Extensions-implemented-in-GNU-Fortran.html#Extensions-implemented-in-GNU-Fortran" accesskey="u" rel="up">Extensions implemented in GNU Fortran</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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<hr>
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<a name="STRUCTURE-and-RECORD-1"></a>
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<h4 class="subsection">6.1.20 <code>STRUCTURE</code> and <code>RECORD</code></h4>
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<a name="index-STRUCTURE"></a>
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<a name="index-RECORD"></a>
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<p>Record structures are a pre-Fortran-90 vendor extension to create
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user-defined aggregate data types. GNU Fortran does not support
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record structures, only Fortran 90’s “derived types”, which have
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a different syntax.
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</p>
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<p>In many cases, record structures can easily be converted to derived types.
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To convert, replace <code>STRUCTURE /</code><var>structure-name</var><code>/</code>
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by <code>TYPE</code> <var>type-name</var>. Additionally, replace
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<code>RECORD /</code><var>structure-name</var><code>/</code> by
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<code>TYPE(</code><var>type-name</var><code>)</code>. Finally, in the component access,
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replace the period (<code>.</code>) by the percent sign (<code>%</code>).
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</p>
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<p>Here is an example of code using the non portable record structure syntax:
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</p>
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<div class="example">
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<pre class="example">! Declaring a structure named ``item'' and containing three fields:
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! an integer ID, an description string and a floating-point price.
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STRUCTURE /item/
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INTEGER id
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CHARACTER(LEN=200) description
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REAL price
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END STRUCTURE
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! Define two variables, an single record of type ``item''
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! named ``pear'', and an array of items named ``store_catalog''
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RECORD /item/ pear, store_catalog(100)
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! We can directly access the fields of both variables
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pear.id = 92316
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pear.description = "juicy D'Anjou pear"
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pear.price = 0.15
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store_catalog(7).id = 7831
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store_catalog(7).description = "milk bottle"
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store_catalog(7).price = 1.2
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! We can also manipulate the whole structure
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store_catalog(12) = pear
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print *, store_catalog(12)
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</pre></div>
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<p>This code can easily be rewritten in the Fortran 90 syntax as following:
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</p>
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<div class="example">
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<pre class="example">! ``STRUCTURE /name/ ... END STRUCTURE'' becomes
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! ``TYPE name ... END TYPE''
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TYPE item
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INTEGER id
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CHARACTER(LEN=200) description
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REAL price
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END TYPE
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! ``RECORD /name/ variable'' becomes ``TYPE(name) variable''
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TYPE(item) pear, store_catalog(100)
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! Instead of using a dot (.) to access fields of a record, the
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! standard syntax uses a percent sign (%)
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pear%id = 92316
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pear%description = "juicy D'Anjou pear"
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pear%price = 0.15
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store_catalog(7)%id = 7831
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store_catalog(7)%description = "milk bottle"
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store_catalog(7)%price = 1.2
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! Assignments of a whole variable do not change
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store_catalog(12) = pear
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print *, store_catalog(12)
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</pre></div>
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<p>GNU Fortran implements STRUCTURES like derived types with the following
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rules and exceptions:
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</p>
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<ul>
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<li> Structures act like derived types with the <code>SEQUENCE</code> attribute.
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Otherwise they may contain no specifiers.
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</li><li> Structures may share names with other symbols. For example, the following
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is invalid for derived types, but valid for structures:
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<div class="smallexample">
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<pre class="smallexample">structure /header/
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! ...
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end structure
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record /header/ header
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</pre></div>
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</li><li> Structure types may be declared nested within another parent structure.
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The syntax is:
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<div class="smallexample">
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<pre class="smallexample">structure /type-name/
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...
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structure [/<type-name>/] <field-list>
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...
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</pre></div>
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<p>The type name may be ommitted, in which case the structure type itself is
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anonymous, and other structures of the same type cannot be instantiated. The
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following shows some examples:
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</p>
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<div class="example">
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<pre class="example">structure /appointment/
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! nested structure definition: app_time is an array of two 'time'
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structure /time/ app_time (2)
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integer(1) hour, minute
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end structure
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character(10) memo
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end structure
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! The 'time' structure is still usable
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record /time/ now
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now = time(5, 30)
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...
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structure /appointment/
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! anonymous nested structure definition
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structure start, end
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integer(1) hour, minute
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end structure
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character(10) memo
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end structure
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</pre></div>
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</li><li> Structures may contain <code>UNION</code> blocks. For more detail see the
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section on <a href="UNION-and-MAP.html#UNION-and-MAP">UNION and MAP</a>.
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</li><li> Structures support old-style initialization of components, like
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those described in <a href="Old_002dstyle-variable-initialization.html#Old_002dstyle-variable-initialization">Old-style variable initialization</a>. For array
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initializers, an initializer may contain a repeat specification of the form
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<code><literal-integer> * <constant-initializer></code>. The value of the integer
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indicates the number of times to repeat the constant initializer when expanding
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the initializer list.
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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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Next: <a href="UNION-and-MAP.html#UNION-and-MAP" accesskey="n" rel="next">UNION and MAP</a>, Previous: <a href="Read_002fWrite-after-EOF-marker.html#Read_002fWrite-after-EOF-marker" accesskey="p" rel="prev">Read/Write after EOF marker</a>, Up: <a href="Extensions-implemented-in-GNU-Fortran.html#Extensions-implemented-in-GNU-Fortran" accesskey="u" rel="up">Extensions implemented in GNU Fortran</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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