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[svn-r1244] Datatypes.html
DatatypesEnum.html EnumMap.gif Added enumeration datatypes -- First pass, only minimal editing. Intro paragraph in Datatypes.html; details in DatatypesEnum.html. EnumMap.gif is a figure for DatatypesEnum.html. Tools.html Added new h5toh4 supported object and data type. H5.intro.html Corrected transposed "start coordinates" in Example 1.
This commit is contained in:
Frank Baker
parent
2ea07058c9
commit
a3d84da7df
@ -1150,7 +1150,21 @@ H5Tinsert (surf_id, "y", HOFFSET(surf_t,y), complex_id);
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</table>
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</center>
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<h2>7. Sharing Data Types among Datasets</h2>
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<a name="Datatypes_Enum"> </a>
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<h2>7. <a href="DatatypesEnum.html">Enumeration Data Types</a></h2>
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An HDF5 enumeration data type is a 1:1 mapping between a set of
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symbols and a set of integer values, and an order is imposed on
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the symbols by their integer values. The symbols are passed
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between the application and library as character strings and all
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the values for a particular enumeration type are of the same
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integer type, which is not necessarily a native type.
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<p>
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Details of enumeration data types and the related functions
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are discussed on a separate
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<a href="DatatypesEnum.html">Enumeration Data Types</a> page.
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<h2>8. Sharing Data Types among Datasets</h2>
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<p>If a file has lots of datasets which have a common data type
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then the file could be made smaller by having all the datasets
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@ -1196,7 +1210,7 @@ hid_t dset4 = H5Dcreate (file, "dset4", t2, space, H5P_DEFAULT);
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</center>
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<a name="Datatypes-DataConversion">
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<h2>8. Data Conversion</h2>
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<h2>9. Data Conversion</h2>
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</a>
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<p>The library is capable of converting data from one type to
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@ -1553,7 +1567,6 @@ H5Tregister(H5T_PERS_SOFT, "cus2be",
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conversion path whether that conversion path was actually used
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or not.
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<<<<<<< Datatypes.html
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<hr>
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@ -1621,7 +1634,7 @@ And in this document, the
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</address>
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<!-- Created: Thu Dec 4 14:57:32 EST 1997 -->
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<!-- hhmts start -->
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Last modified: Wed Dec 16 13:04:58 EST 1998
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Last modified: 30 April 1999
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<!-- hhmts end -->
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921
doc/html/DatatypesEnum.html
Normal file
921
doc/html/DatatypesEnum.html
Normal file
@ -0,0 +1,921 @@
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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
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<html>
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<head>
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<title>Enumeration Data Types in the Data Type Interface (H5T)</title>
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</head>
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<body bgcolor="#FFFFFF">
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<hr>
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<center>
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<table border=0 width=98%>
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<tr><td valign=top align=left>
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<a href="H5.intro.html">Introduction to HDF5</a> <br>
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<a href="RM_H5Front.html">HDF5 Reference Manual</a> <br>
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<a href="index.html">Other HDF5 documents and links</a> <br>
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<!--
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<a href="Glossary.html">Glossary</a><br>
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-->
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</td>
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<td valign=top align=right>
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And in this document, the
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<a href="H5.user.html">HDF5 User's Guide</a>:
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<a href="Files.html">Files</a>
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<br>
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<a href="Datasets.html">Datasets</a>
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<a href="Datatypes.html">Data Types</a>
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<a href="Dataspaces.html">Dataspaces</a>
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<a href="Groups.html">Groups</a>
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<a href="References.html">References</a>
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<br>
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<a href="Attributes.html">Attributes</a>
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<a href="Properties.html">Property Lists</a>
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<a href="Errors.html">Error Handling</a>
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<a href="Filters.html">Filters</a>
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<a href="Caching.html">Caching</a>
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<br>
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<a href="Chunking.html">Chunking</a>
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<a href="Debugging.html">Debugging</a>
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<a href="Environment.html">Environment</a>
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<a href="ddl.html">DDL</a>
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<a href="Ragged.html">Ragged Arrays</a>
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<!--
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<hr>
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And in this document, the
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<a href="H5.user.html">HDF5 User's Guide</a>:
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<a href="Attributes.html">H5A</a>
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<a href="Datasets.html">H5D</a>
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<a href="Errors.html">H5E</a>
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<a href="Files.html">H5F</a>
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<a href="Groups.html">H5G</a>
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<a href="Properties.html">H5P</a>
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<a href="References.html">H5R & H5I</a>
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<a href="Ragged.html">H5RA</a>
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<a href="Dataspaces.html">H5S</a>
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<a href="Datatypes.html">H5T</a>
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<a href="Filters.html">H5Z</a>
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<a href="Caching.html">Caching</a>
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<a href="Chunking.html">Chunking</a>
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<a href="Debugging.html">Debugging</a>
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<a href="Environment.html">Environment</a>
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<a href="ddl.html">DDL</a>
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-->
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</td></tr>
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</table>
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</center>
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<hr>
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<h1>The Data Type Interface (H5T) <font size=-1><i>(contitnued)</i></font></h1>
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<p align=right><font size=-1><i>
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(Return to <a href="Datatypes.html#Datatypes_Enum">Data Types Interface (H5T)</a>.)
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</font></i>
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<h2>7. Enumeration Data Types</h2>
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<h3>7.1. Introduction</h2>
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<p>An HDF enumeration data type is a 1:1 mapping between a set of
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symbols and a set of integer values, and an order is imposed on
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the symbols by their integer values. The symbols are passed
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between the application and library as character strings and all
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the values for a particular enumeration type are of the same
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integer type, which is not necessarily a native type.
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<h3>7.2. Creation</h2>
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<p>Creation of an enumeration data type resembles creation of a
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compound data type: first an empty enumeration type is created,
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then members are added to the type, then the type is optionally
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locked.
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<dl>
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<dt><code>hid_t H5Tcreate(H5T_class_t <em>type_class</em>,
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size_t <em>size</em>)</code>
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<dd>This function creates a new empty enumeration data type based
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on a native signed integer type. The first argument is the
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constant <code>H5T_ENUM</code> and the second argument is the
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size in bytes of the native integer on which the enumeration
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type is based. If the architecture does not support a native
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signed integer of the specified size then an error is
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returned.
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<pre>
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/* Based on a native signed short */
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hid_t hdf_en_colors = H5Tcreate(H5T_ENUM, sizeof(short));</pre>
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<dt><code>hid_t H5Tenum_create(hid_t <em>base</em>)</code>
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<dd>This function creates a new empty enumeration data type based
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on some integer data type <em>base</em> and is a
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generalization of the <code>H5Tcreate()</code> function. This
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function is useful when creating an enumeration type based on
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some non-native integer data type, but it can be used for
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native types as well.
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<pre>
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/* Based on a native unsigned short */
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hid_t hdf_en_colors_1 = H5Tenum_create(H5T_NATIVE_USHORT);
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/* Based on a MIPS 16-bit unsigned integer */
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hid_t hdf_en_colors_2 = H5Tenum_create(H5T_MIPS_UINT16);
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/* Based on a big-endian 16-bit unsigned integer */
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hid_t hdf_en_colors_3 = H5Tenum_create(H5T_STD_U16BE);</pre>
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<dt><code>herr_t H5Tenum_insert(hid_t <em>etype</em>, const char
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*<em>symbol</em>, void *<em>value</em>)</code>
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<dd>Members are inserted into the enumeration data type
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<em>etype</em> with this function. Each member has a symbolic
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name <em>symbol</em> and some integer representation
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<em>value</em>. The <em>value</em> argument must point to a value
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of the same data type as specified when the enumeration type
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was created. The order of member insertion is not important
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but all symbol names and values must be unique within a
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particular enumeration type.
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<pre>
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short val;
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H5Tenum_insert(hdf_en_colors, "RED", (val=0,&val));
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H5Tenum_insert(hdf_en_colors, "GREEN", (val=1,&val));
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H5Tenum_insert(hdf_en_colors, "BLUE", (val=2,&val));
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H5Tenum_insert(hdf_en_colors, "WHITE", (val=3,&val));
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H5Tenum_insert(hdf_en_colors, "BLACK", (val=4,&val));</pre>
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<dt><code>herr_t H5Tlock(hid_t <em>etype</em>)</code>
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<dd>This function locks a data type so it cannot be modified or
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freed unless the entire HDF5 library is closed. Its use is
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completely optional but using it on an application data type
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makes that data type act like a predefined data type.
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<pre>
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H5Tlock(hdf_en_colors);</pre>
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</dl>
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<h3>7.3. Integer Operations</h2>
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<p>Because an enumeration data type is derived from an integer
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data type, any operation which can be performed on integer data
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types can also be performed on enumeration data types. This
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includes:
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<p>
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<center>
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<table>
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<tr>
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<td><code>H5Topen()</code></td>
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<td><code>H5Tcreate()</code></td>
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<td><code>H5Tcopy()</code></td>
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<td><code>H5Tclose()</code></td>
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</tr><tr>
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<td><code>H5Tequal()</code></td>
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<td><code>H5Tlock()</code></td>
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<td><code>H5Tcommit()</code></td>
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<td><code>H5Tcommitted()</code></td>
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</tr><tr>
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<td><code>H5Tget_class()</code></td>
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<td><code>H5Tget_size()</code></td>
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<td><code>H5Tget_order()</code></td>
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<td><code>H5Tget_pad()</code></td>
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</tr><tr>
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<td><code>H5Tget_precision()</code></td>
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<td><code>H5Tget_offset()</code></td>
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<td><code>H5Tget_sign()</code></td>
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<td><code>H5Tset_size()</code></td>
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</tr><tr>
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<td><code>H5Tset_order()</code></td>
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<td><code>H5Tset_precision()</code></td>
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<td><code>H5Tset_offset()</code></td>
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<td><code>H5Tset_pad()</code></td>
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</tr><tr>
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<td><code>H5Tset_sign()</code></td>
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</tr>
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</table>
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</center>
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<p>In addition, the new function <code>H5Tget_super()</code> will
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be defined for all data types that are derived from existing
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types (currently just enumeration types).
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<dl>
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<dt><code>hid_t H5Tget_super(hid_t <em>type</em>)</code>
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<dd>Return the data type from which <em>type</em> is
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derived. When <em>type</em> is an enumeration data type then
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the returned value will be an integer data type but not
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necessarily a native type. One use of this function would be
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to create a new enumeration type based on the same underlying
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integer type and values but with possibly different symbols.
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<pre>
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hid_t itype = H5Tget_super(hdf_en_colors);
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hid_t hdf_fr_colors = H5Tenum_create(itype);
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H5Tclose(itype);
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short val;
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H5Tenum_insert(hdf_fr_colors, "ouge", (val=0,&val));
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H5Tenum_insert(hdf_fr_colors, "vert", (val=1,&val));
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H5Tenum_insert(hdf_fr_colors, "bleu", (val=2,&val));
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H5Tenum_insert(hdf_fr_colors, "blanc", (val=3,&val));
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H5Tenum_insert(hdf_fr_colors, "noir", (val=4,&val));
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H5Tlock(hdf_fr_colors);</pre>
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</dl>
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<h3>7.4. Type Functions</h2>
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<p>A small set of functions is available for querying properties
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of an enumeration type. These functions are likely to be used
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by browsers to display data type information.
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<dl>
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<dt><code>int H5Tget_nmembers(hid_t <em>etype</em>)</code>
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<dd>When given an enumeration data type <em>etype</em> this
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function returns the number of members defined for that
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type. This function is already implemented for compound data
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types.
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<br><br>
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<dt><code>char *H5Tget_member_name(hid_t <em>etype</em>, int
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<em>membno</em>)</code>
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<dd>Given an enumeration data type <em>etype</em> this function
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returns the symbol name for the member indexed by
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<em>membno</em>. Members are numbered from zero to
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<em>N</em>-1 where <em>N</em> is the return value from
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<code>H5Tget_nmembers()</code>. The members are stored in no
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particular order. This function is already implemented for
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compound data types. If an error occurs then the null pointer
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is returned. The return value should be freed by calling
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<code>free()</code>.
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<br><br>
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<dt><code>herr_t H5Tget_member_value(hid_t <em>etype</em>, int
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<em>membno</em>, void *<em>value</em>/*out*/)</code>
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<dd>Given an enumeration data type <em>etype</em> this function
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returns the value associated with the member indexed by
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<em>membno</em> (as described for
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<code>H5Tget_member_name()</code>). The value returned
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is in the domain of the underlying integer
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data type which is often a native integer type. The
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application should ensure that the memory pointed to by
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<em>value</em> is large enough to contain the result (the size
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can be obtained by calling <code>H5Tget_size()</code> on
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either the enumeration type or the underlying integer type
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when the type is not known by the C compiler.
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<pre>
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int i, n = H5Tget_nmembers(hdf_en_colors);
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for (i=0; i<n; i++) {
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char *symbol = H5Tget_member_name(hdf_en_colors, i);
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short val;
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H5Tget_member_value(hdf_en_colors, i, &val);
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printf("#%d %20s = %d\n", i, symbol, val);
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free(symbol);
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}</pre>
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<p>
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Output:
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<pre>
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#0 BLACK = 4
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#1 BLUE = 2
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#2 GREEN = 1
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#3 RED = 0
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#4 WHITE = 3</pre>
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</dl>
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<h3>7.5. Data Functions</h2>
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<p>In addition to querying about the enumeration type properties,
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an application may want to make queries about enumerated
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data. These functions perform efficient mappings between symbol
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names and values.
|
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|
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<dl>
|
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<dt><code>herr_t H5Tenum_valueof(hid_t <em>etype</em>, const char
|
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*<em>symbol</em>, void *<em>value</em>/*out*/)</code>
|
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<dd>Given an enumeration data type <em>etype</em> this function
|
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returns through <em>value</em> the bit pattern associated with
|
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the symbol name <em>symbol</em>. The <em>value</em> argument
|
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should point to memory which is large enough to hold the result,
|
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which is returned as the underlying integer data type specified
|
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when the enumeration type was created, often a native integer
|
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type.
|
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|
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<br><br>
|
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<dt><code>herr_t H5Tenum_nameof(hid_t <em>etype</em>, void
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*<em>value</em>, char *<em>symbol</em>, size_t
|
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<em>size</em>)</code>
|
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<dd>This function translates a bit pattern pointed to by
|
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<em>value</em> to a symbol name according to the mapping
|
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defined in the enumeration data type <em>etype</em> and stores
|
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at most <em>size</em> characters of that name (counting the
|
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null terminator) to the <em>symbol</em> buffer. If the name is
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longer than the result buffer then the result is not null
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terminated and the function returns failure. If <em>value</em>
|
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points to a bit pattern which is not in the domain of the
|
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enumeration type then the first byte of the <em>symbol</em>
|
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buffer is set to zero and the function fails.
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|
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<pre>
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short data[1000] = {4, 2, 0, 0, 5, 1, ...};
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int i;
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char symbol[32];
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for (i=0; i<1000; i++) {
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if (H5Tenum_nameof(hdf_en_colors, data+i, symbol,
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sizeof symbol))<0) {
|
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if (symbol[0]) {
|
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strcpy(symbol+sizeof(symbol)-4, "...");
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} else {
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strcpy(symbol, "UNKNOWN");
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}
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}
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printf("%d %s\n", data[i], symbol);
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}
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printf("}\n");</pre>
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<p>
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Output:
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<pre>
|
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|
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4 BLACK
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2 BLUE
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0 RED
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0 RED
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5 UNKNOWN
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1 GREEN
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...</pre>
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</dl>
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|
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<h3>7.6. Conversion</h2>
|
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|
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<p>Enumerated data can be converted from one type to another
|
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provided the destination enumeration type contains all the
|
||||
symbols of the source enumeration type. The conversion operates
|
||||
by matching up the symbol names of the source and destination
|
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enumeration types to build a mapping from source value to
|
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destination value. For instance, if we are translating from an
|
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enumeration type that defines a sequence of integers as the
|
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values for the colors to a type that defines a different bit for
|
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each color then the mapping might look like this:
|
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|
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<p><img src="EnumMap.gif" alt="Enumeration Mapping">
|
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|
||||
<p>That is, a source value of <code>2</code> which corresponds to
|
||||
<code>BLUE</code> would be mapped to <code>0x0004</code>. The
|
||||
following code snippet builds the second data type, then
|
||||
converts a raw data array from one data type to another, and
|
||||
then prints the result.
|
||||
|
||||
<pre>
|
||||
/* Create a new enumeration type */
|
||||
short val;
|
||||
hid_t bits = H5Tcreate(H5T_ENUM, sizeof val);
|
||||
H5Tenum_insert(bits, "RED", (val=0x0001,&val));
|
||||
H5Tenum_insert(bits, "GREEN", (val=0x0002,&val));
|
||||
H5Tenum_insert(bits, "BLUE", (val=0x0004,&val));
|
||||
H5Tenum_insert(bits, "WHITE", (val=0x0008,&val));
|
||||
H5Tenum_insert(bits, "BLACK", (val=0x0010,&val));
|
||||
|
||||
/* The data */
|
||||
short data[6] = {1, 4, 2, 0, 3, 5};
|
||||
|
||||
/* Convert the data from one type to another */
|
||||
H5Tconvert(hdf_en_colors, bits, 5, data, NULL);
|
||||
|
||||
/* Print the data */
|
||||
for (i=0; i<6; i++) {
|
||||
printf("0x%04x\n", (unsigned)(data[i]));
|
||||
}</pre>
|
||||
|
||||
<p>
|
||||
Output:
|
||||
<pre>
|
||||
|
||||
0x0002
|
||||
0x0010
|
||||
0x0004
|
||||
0x0001
|
||||
0x0008
|
||||
0xffff</pre>
|
||||
|
||||
<p>If the source data stream contains values which are not in the
|
||||
domain of the conversion map then an overflow exception is
|
||||
raised within the library, causing the application defined
|
||||
overflow handler to be invoked (see
|
||||
<code>H5Tset_overflow()</code>). If no overflow handler is
|
||||
defined then all bits of the destination value will be set.
|
||||
|
||||
<p>The HDF library will not provide conversions between enumerated
|
||||
data and integers although the application is free to do so
|
||||
(this is a policy we apply to all classes of HDF data
|
||||
types). However, since enumeration types are derived from
|
||||
integer types it is permissible to treat enumerated data as
|
||||
integers and perform integer conversions in that context.
|
||||
|
||||
<h3>7.7. Symbol Order</h2>
|
||||
|
||||
<p>Symbol order is determined by the integer values associated
|
||||
with each symbol. When the integer data type is a native type,
|
||||
testing the relative order of two symbols is an easy process:
|
||||
simply compare the values of the symbols. If only the symbol
|
||||
names are available then the values must first be determined by
|
||||
calling <code>H5Tenum_valueof()</code>.
|
||||
|
||||
<pre>
|
||||
short val1, val2;
|
||||
H5Tenum_valueof(hdf_en_colors, "WHITE", &val1);
|
||||
H5Tenum_valueof(hdf_en_colors, "BLACK", &val2);
|
||||
if (val1 < val2) ...</pre>
|
||||
|
||||
<p>When the underlying integer data type is not a native type then
|
||||
the easiest way to compare symbols is to first create a similar
|
||||
enumeration type that contains all the same symbols but has a
|
||||
native integer type (HDF type conversion features can be used to
|
||||
convert the non-native values to native values). Once we have a
|
||||
native type we can compare symbol order as just described. If
|
||||
<code>foreign</code> is some non-native enumeration type then a
|
||||
native type can be created as follows:
|
||||
|
||||
<pre>
|
||||
int n = H5Tget_nmembers(foreign);
|
||||
hid_t itype = H5Tget_super(foreign);
|
||||
void *val = malloc(n * MAX(H5Tget_size(itype), sizeof(int)));
|
||||
char *name = malloc(n * sizeof(char*));
|
||||
int i;
|
||||
|
||||
/* Get foreign type information */
|
||||
for (i=0; i<n; i++) {
|
||||
name[i] = H5Tget_member_name(foreign, i);
|
||||
H5Tget_member_value(foreign, i,
|
||||
(char*)val+i*H5Tget_size(foreign));
|
||||
}
|
||||
|
||||
/* Convert integer values to new type */
|
||||
H5Tconvert(itype, H5T_NATIVE_INT, n, val, NULL);
|
||||
|
||||
/* Build a native type */
|
||||
hid_t native = H5Tenum_create(H5T_NATIVE_INT);
|
||||
for (i=0; i<n; i++) {
|
||||
H5Tenum_insert(native, name[i], ((int*)val)[i]);
|
||||
free(name[i]);
|
||||
}
|
||||
free(name);
|
||||
free(val);</pre>
|
||||
|
||||
<p>It is also possible to convert enumerated data to a new type
|
||||
that has a different order defined for the symbols. For
|
||||
instance, we can define a new type, <code>reverse</code> that
|
||||
defines the same five colors but in the reverse order.
|
||||
|
||||
<pre>
|
||||
short val;
|
||||
int i;
|
||||
char sym[8];
|
||||
short data[5] = {0, 1, 2, 3, 4};
|
||||
|
||||
hid_t reverse = H5Tenum_create(H5T_NATIVE_SHORT);
|
||||
H5Tenum_insert(reverse, "BLACK", (val=0,&val));
|
||||
H5Tenum_insert(reverse, "WHITE", (val=1,&val));
|
||||
H5Tenum_insert(reverse, "BLUE", (val=2,&val));
|
||||
H5Tenum_insert(reverse, "GREEN", (val=3,&val));
|
||||
H5Tenum_insert(reverse, "RED", (val=4,&val));
|
||||
|
||||
/* Print data */
|
||||
for (i=0; i<5; i++) {
|
||||
H5Tenum_nameof(hdf_en_colors, data+i, sym, sizeof sym);
|
||||
printf ("%d %s\n", data[i], sym);
|
||||
}
|
||||
|
||||
puts("Converting...");
|
||||
H5Tconvert(hdf_en_colors, reverse, 5, data, NULL);
|
||||
|
||||
/* Print data */
|
||||
for (i=0; i<5; i++) {
|
||||
H5Tenum_nameof(reverse, data+i, sym, sizeof sym);
|
||||
printf ("%d %s\n", data[i], sym);
|
||||
}</pre>
|
||||
|
||||
<p>
|
||||
Output:
|
||||
<pre>
|
||||
0 RED
|
||||
1 GREEN
|
||||
2 BLUE
|
||||
3 WHITE
|
||||
4 BLACK
|
||||
Converting...
|
||||
4 RED
|
||||
3 GREEN
|
||||
2 BLUE
|
||||
1 WHITE
|
||||
0 BLACK</pre>
|
||||
|
||||
<h3>7.8. Equality</h2>
|
||||
|
||||
<p>The order that members are inserted into an enumeration type is
|
||||
unimportant; the important part is the associations between the
|
||||
symbol names and the values. Thus, two enumeration data types
|
||||
will be considered equal if and only if both types have the same
|
||||
symbol/value associations and both have equal underlying integer
|
||||
data types. Type equality is tested with the
|
||||
<code>H5Tequal()</code> function.
|
||||
|
||||
<h3>7.9. Interacting with C's <code>enum</code> Type</h2>
|
||||
|
||||
<p>Although HDF enumeration data types are similar to C
|
||||
<code>enum</code> data types, there are some important
|
||||
differences:
|
||||
|
||||
<p>
|
||||
<center>
|
||||
<table border width="80%">
|
||||
<tr>
|
||||
<th>Difference</th>
|
||||
<th>Motivation/Implications</th>
|
||||
</tr>
|
||||
|
||||
<tr>
|
||||
<td valign=top>Symbols are unquoted in C but quoted in
|
||||
HDF.</td>
|
||||
<td valign=top>This allows the application to manipulate
|
||||
symbol names in ways that are not possible with C.</td>
|
||||
</tr>
|
||||
|
||||
<tr>
|
||||
<td valign=top>The C compiler automatically replaces all
|
||||
symbols with their integer values but HDF requires
|
||||
explicit calls to do the same.</td>
|
||||
<td valign=top>C resolves symbols at compile time while
|
||||
HDF resolves symbols at run time.</td>
|
||||
</tr>
|
||||
|
||||
<tr>
|
||||
<td valign=top>The mapping from symbols to integers is
|
||||
<em>N</em>:1 in C but 1:1 in HDF.</td>
|
||||
<td valign=top>HDF can translate from value to name
|
||||
uniquely and large <code>switch</code> statements are
|
||||
not necessary to print values in human-readable
|
||||
format.</td>
|
||||
</tr>
|
||||
|
||||
<tr>
|
||||
<td valign=top>A symbol must appear in only one C
|
||||
<code>enum</code> type but may appear in multiple HDF
|
||||
enumeration types.</td>
|
||||
<td valign=top>The translation from symbol to value in HDF
|
||||
requires the data type to be specified while in C the
|
||||
data type is not necessary because it can be inferred
|
||||
from the symbol.</td>
|
||||
</tr>
|
||||
|
||||
<tr>
|
||||
<td valign=top>The underlying integer value is always a
|
||||
native integer in C but can be a foreign integer type in
|
||||
HDF.</td>
|
||||
<td valign=top>This allows HDF to describe data that might
|
||||
reside on a foreign architecture, such as data stored in
|
||||
a file.</td>
|
||||
</tr>
|
||||
|
||||
<tr>
|
||||
<td valign=top>The sign and size of the underlying integer
|
||||
data type is chosen automatically by the C compiler but
|
||||
must be fully specified with HDF.</td>
|
||||
<td valign=top>Since HDF doesn't require finalization of a
|
||||
data type, complete specification of the type must be
|
||||
supplied before the type is used. Requiring that
|
||||
information at the time of type creation was a design
|
||||
decision to simplify the library.</td>
|
||||
</tr>
|
||||
</table>
|
||||
</center>
|
||||
|
||||
<p>The examples below use the following C data types:
|
||||
|
||||
<p>
|
||||
<table width="90%" bgcolor="white">
|
||||
<tr>
|
||||
<td>
|
||||
<code><pre>
|
||||
/* English color names */
|
||||
typedef enum {
|
||||
RED,
|
||||
GREEN,
|
||||
BLUE,
|
||||
WHITE,
|
||||
BLACK
|
||||
} c_en_colors;
|
||||
|
||||
/* Spanish color names, reverse order */
|
||||
typedef enum {
|
||||
NEGRO
|
||||
BLANCO,
|
||||
AZUL,
|
||||
VERDE,
|
||||
ROJO,
|
||||
} c_sp_colors;
|
||||
|
||||
/* No enum definition for French names */
|
||||
</pre></code>
|
||||
</td>
|
||||
</tr>
|
||||
</table>
|
||||
|
||||
<h4>Creating HDF Types from C Types</h3>
|
||||
|
||||
<p>An HDF enumeration data type can be created from a C
|
||||
<code>enum</code> type simply by passing pointers to the C
|
||||
<code>enum</code> values to <code>H5Tenum_insert()</code>. For
|
||||
instance, to create HDF types for the <code>c_en_colors</code>
|
||||
type shown above:
|
||||
|
||||
<p>
|
||||
<table width="90%" bgcolor="white">
|
||||
<tr>
|
||||
<td>
|
||||
<code><pre>
|
||||
|
||||
c_en_colors val;
|
||||
hid_t hdf_en_colors = H5Tcreate(H5T_ENUM, sizeof(c_en_colors));
|
||||
H5Tenum_insert(hdf_en_colors, "RED", (val=RED, &val));
|
||||
H5Tenum_insert(hdf_en_colors, "GREEN", (val=GREEN,&val));
|
||||
H5Tenum_insert(hdf_en_colors, "BLUE", (val=BLUE, &val));
|
||||
H5Tenum_insert(hdf_en_colors, "WHITE", (val=WHITE,&val));
|
||||
H5Tenum_insert(hdf_en_colors, "BLACK", (val=BLACK,&val));</pre></code>
|
||||
</td>
|
||||
</tr>
|
||||
</table>
|
||||
|
||||
<h4>Name Changes between Applications</h3>
|
||||
|
||||
<p>Occassionally two applicatons wish to exchange data but they
|
||||
use different names for the constants they exchange. For
|
||||
instance, an English and a Spanish program may want to
|
||||
communicate color names although they use different symbols in
|
||||
the C <code>enum</code> definitions. The communication is still
|
||||
possible although the applications must agree on common terms
|
||||
for the colors. The following example shows the Spanish code to
|
||||
read the values assuming that the applications have agreed that
|
||||
the color information will be exchanged using Enlish color
|
||||
names:
|
||||
|
||||
<p>
|
||||
<table width="90%" bgcolor="white">
|
||||
<tr>
|
||||
<td>
|
||||
<code><pre>
|
||||
|
||||
c_sp_colors val, data[1000];
|
||||
hid_t hdf_sp_colors = H5Tcreate(H5T_ENUM, sizeof(c_sp_colors));
|
||||
H5Tenum_insert(hdf_sp_colors, "RED", (val=ROJO, &val));
|
||||
H5Tenum_insert(hdf_sp_colors, "GREEN", (val=VERDE, &val));
|
||||
H5Tenum_insert(hdf_sp_colors, "BLUE", (val=AZUL, &val));
|
||||
H5Tenum_insert(hdf_sp_colors, "WHITE", (val=BLANCO, &val));
|
||||
H5Tenum_insert(hdf_sp_colors, "BLACK", (val=NEGRO, &val));
|
||||
|
||||
H5Dread(dataset, hdf_sp_colors, H5S_ALL, H5S_ALL, H5P_DEFAULT, data);</pre></code>
|
||||
</td>
|
||||
</tr>
|
||||
</table>
|
||||
|
||||
|
||||
<h4>Symbol Ordering across Applications</h3>
|
||||
|
||||
<p>Since symbol ordering is completely determined by the integer values
|
||||
assigned to each symbol in the <code>enum</code> definition,
|
||||
ordering of <code>enum</code> symbols cannot be preserved across
|
||||
files like with HDF enumeration types. HDF can convert from one
|
||||
application's integer values to the other's so a symbol in one
|
||||
application's C <code>enum</code> gets mapped to the same symbol
|
||||
in the other application's C <code>enum</code>, but the relative
|
||||
order of the symbols is not preserved.
|
||||
|
||||
<p>For example, an application may be defined to use the
|
||||
definition of <code>c_en_colors</code> defined above where
|
||||
<code>WHITE</code> is less than <code>BLACK</code>, but some
|
||||
other application might define the colors in some other
|
||||
order. If each application defines an HDF enumeration type based
|
||||
on that application's C <code>enum</code> type then HDF will
|
||||
modify the integer values as data is communicated from one
|
||||
application to the other so that a <code>RED</code> value
|
||||
in the first application is also a <code>RED</code> value in the
|
||||
other application.
|
||||
|
||||
<p>A case of this reordering of symbol names was also shown in the
|
||||
previous code snippet (as well as a change of language), where
|
||||
HDF changed the integer values so 0 (<code>RED</code>) in the
|
||||
input file became 4 (<code>ROJO</code>) in the <code>data</code>
|
||||
array. In the input file, <code>WHITE</code> was less than
|
||||
<code>BLACK</code>; in the application the opposite is true.
|
||||
|
||||
<p>In fact, the ability to change the order of symbols is often
|
||||
convenient when the enumeration type is used only to group
|
||||
related symbols that don't have any well defined order
|
||||
relationship.
|
||||
|
||||
<h4>Internationalization</h3>
|
||||
|
||||
<p>The HDF enumeration type conversion features can also be used
|
||||
to provide internationalization of debugging output. A program
|
||||
written with the <code>c_en_colors</code> data type could define
|
||||
a separate HDF data type for languages such as English, Spanish,
|
||||
and French and cast the enumerated value to one of these HDF
|
||||
types to print the result.
|
||||
|
||||
<p>
|
||||
<table width="90%" bgcolor="white">
|
||||
<tr>
|
||||
<td>
|
||||
<code><pre>
|
||||
|
||||
c_en_colors val, *data=...;
|
||||
|
||||
hid_t hdf_sp_colors = H5Tcreate(H5T_ENUM, sizeof val);
|
||||
H5Tenum_insert(hdf_sp_colors, "ROJO", (val=RED, &val));
|
||||
H5Tenum_insert(hdf_sp_colors, "VERDE", (val=GREEN, &val));
|
||||
H5Tenum_insert(hdf_sp_colors, "AZUL", (val=BLUE, &val));
|
||||
H5Tenum_insert(hdf_sp_colors, "BLANCO", (val=WHITE, &val));
|
||||
H5Tenum_insert(hdf_sp_colors, "NEGRO", (val=BLACK, &val));
|
||||
|
||||
hid_t hdf_fr_colors = H5Tcreate(H5T_ENUM, sizeof val);
|
||||
H5Tenum_insert(hdf_fr_colors, "OUGE", (val=RED, &val));
|
||||
H5Tenum_insert(hdf_fr_colors, "VERT", (val=GREEN, &val));
|
||||
H5Tenum_insert(hdf_fr_colors, "BLEU", (val=BLUE, &val));
|
||||
H5Tenum_insert(hdf_fr_colors, "BLANC", (val=WHITE, &val));
|
||||
H5Tenum_insert(hdf_fr_colors, "NOIR", (val=BLACK, &val));
|
||||
|
||||
void
|
||||
nameof(lang_t language, c_en_colors val, char *name, size_t size)
|
||||
{
|
||||
switch (language) {
|
||||
case ENGLISH:
|
||||
H5Tenum_nameof(hdf_en_colors, &val, name, size);
|
||||
break;
|
||||
case SPANISH:
|
||||
H5Tenum_nameof(hdf_sp_colors, &val, name, size);
|
||||
break;
|
||||
case FRENCH:
|
||||
H5Tenum_nameof(hdf_fr_colors, &val, name, size);
|
||||
break;
|
||||
}
|
||||
}</pre></code>
|
||||
</td>
|
||||
</tr>
|
||||
</table>
|
||||
|
||||
<h3>7.10. Goals That Have Been Met</h2>
|
||||
|
||||
<p>The main goal of enumeration types is to provide communication
|
||||
of enumerated data using symbolic equivalence. That is, a
|
||||
symbol written to a dataset by one application should be read as
|
||||
the same symbol by some other application.
|
||||
|
||||
<p>
|
||||
<table width="90%">
|
||||
<tr>
|
||||
<td valign=top><b>Architecture Independence</b></td>
|
||||
<td valign=top>Two applications shall be able to exchange
|
||||
enumerated data even when the underlying integer values
|
||||
have different storage formats. HDF accomplishes this for
|
||||
enumeration types by building them upon integer types.</td>
|
||||
</tr>
|
||||
|
||||
<tr>
|
||||
<td valign=top><b>Preservation of Order Relationship</b></td>
|
||||
<td valign=top>The relative order of symbols shall be
|
||||
preserved between two applications that use equivalent
|
||||
enumeration data types. Unlike numeric values that have
|
||||
an implicit ordering, enumerated data has an explicit
|
||||
order defined by the enumeration data type and HDF
|
||||
records this order in the file.</td>
|
||||
</tr>
|
||||
|
||||
<tr>
|
||||
<td valign=top><b>Order Independence</b></td>
|
||||
<td valign=top>An application shall be able to change the
|
||||
relative ordering of the symbols in an enumeration data
|
||||
type. This is accomplished by defining a new type with
|
||||
different integer values and converting data from one type
|
||||
to the other.</td>
|
||||
</tr>
|
||||
|
||||
<tr>
|
||||
<td valign=top><b>Subsets</b></td>
|
||||
<td valign=top>An application shall be able to read
|
||||
enumerated data from an archived dataset even after the
|
||||
application has defined additional members for the
|
||||
enumeration type. An application shall be able to write
|
||||
to a dataset when the dataset contains a superset of the
|
||||
members defined by the application. Similar rules apply
|
||||
for in-core conversions between enumerated data
|
||||
types.</td>
|
||||
</tr>
|
||||
|
||||
<tr>
|
||||
<td valign=top><b>Targetable</b></td>
|
||||
<td valign=top>An application shall be able to target a
|
||||
particular architecture or application when storing
|
||||
enumerated data. This is accomplished by allowing
|
||||
non-native underlying integer types and converting the
|
||||
native data to non-native data.</td>
|
||||
</tr>
|
||||
|
||||
<tr>
|
||||
<td valign=top><b>Efficient Data Transfer</b></td>
|
||||
<td valign=top>An application that defines a file dataset
|
||||
that corresponds to some native C enumerated data array
|
||||
shall be able to read and write to that dataset directly
|
||||
using only Posix read and write functions. HDF already
|
||||
optimizes this case for integers, so the same optimization
|
||||
will apply to enumerated data.
|
||||
</tr>
|
||||
|
||||
<tr>
|
||||
<td valign=top><b>Efficient Storage</b></td>
|
||||
<td valign=top>Enumerated data shall be stored in a manner
|
||||
which is space efficient. HDF stores the enumerated data
|
||||
as integers and allows the application to chose the size
|
||||
and format of those integers.</td>
|
||||
</tr>
|
||||
</table>
|
||||
|
||||
|
||||
<p align=right><font size=-1><i>
|
||||
(Return to <a href="Datatypes.html#Datatypes_Enum">Data Types Interface (H5T)</a>.)
|
||||
</font></i>
|
||||
|
||||
<hr>
|
||||
<center>
|
||||
<table border=0 width=98%>
|
||||
<tr><td valign=top align=left>
|
||||
<a href="H5.intro.html">Introduction to HDF5</a> <br>
|
||||
<a href="RM_H5Front.html">HDF5 Reference Manual</a> <br>
|
||||
<a href="index.html">Other HDF5 documents and links</a> <br>
|
||||
<!--
|
||||
<a href="Glossary.html">Glossary</a><br>
|
||||
-->
|
||||
</td>
|
||||
<td valign=top align=right>
|
||||
And in this document, the
|
||||
<a href="H5.user.html">HDF5 User's Guide</a>:
|
||||
<a href="Files.html">Files</a>
|
||||
<br>
|
||||
<a href="Datasets.html">Datasets</a>
|
||||
Data Types
|
||||
<a href="Dataspaces.html">Dataspaces</a>
|
||||
<a href="Groups.html">Groups</a>
|
||||
<a href="References.html">References</a>
|
||||
<br>
|
||||
<a href="Attributes.html">Attributes</a>
|
||||
<a href="Properties.html">Property Lists</a>
|
||||
<a href="Errors.html">Error Handling</a>
|
||||
<a href="Filters.html">Filters</a>
|
||||
<a href="Caching.html">Caching</a>
|
||||
<br>
|
||||
<a href="Chunking.html">Chunking</a>
|
||||
<a href="Debugging.html">Debugging</a>
|
||||
<a href="Environment.html">Environment</a>
|
||||
<a href="ddl.html">DDL</a>
|
||||
<a href="Ragged.html">Ragged Arrays</a>
|
||||
<!--
|
||||
<hr>
|
||||
And in this document, the
|
||||
<a href="H5.user.html">HDF5 User's Guide</a>:
|
||||
<a href="Attributes.html">H5A</a>
|
||||
<a href="Datasets.html">H5D</a>
|
||||
<a href="Errors.html">H5E</a>
|
||||
<a href="Files.html">H5F</a>
|
||||
<a href="Groups.html">H5G</a>
|
||||
<a href="Properties.html">H5P</a>
|
||||
<a href="References.html">H5R & H5I</a>
|
||||
<a href="Ragged.html">H5RA</a>
|
||||
<a href="Dataspaces.html">H5S</a>
|
||||
<a href="Datatypes.html">H5T</a>
|
||||
<a href="Filters.html">H5Z</a>
|
||||
<a href="Caching.html">Caching</a>
|
||||
<a href="Chunking.html">Chunking</a>
|
||||
<a href="Debugging.html">Debugging</a>
|
||||
<a href="Environment.html">Environment</a>
|
||||
<a href="ddl.html">DDL</a>
|
||||
-->
|
||||
</td></tr>
|
||||
</table>
|
||||
</center>
|
||||
|
||||
|
||||
<hr>
|
||||
<address>
|
||||
<a href="mailto:hdfhelp@ncsa.uiuc.edu">HDF Help Desk</a>
|
||||
</address>
|
||||
<!-- Created: Thu Dec 4 14:57:32 EST 1997 -->
|
||||
<!-- hhmts start -->
|
||||
Last modified: 30 April 1999
|
||||
<!-- hhmts end -->
|
||||
|
||||
|
||||
</body>
|
||||
</html>
|
||||
BIN
doc/html/EnumMap.gif
Normal file
BIN
doc/html/EnumMap.gif
Normal file
Binary file not shown.
|
After Width: | Height: | Size: 1.6 KiB |
@ -696,7 +696,7 @@ the data is stored in another union of hyperslabs in the memory dataspace.
|
||||
<FONT FACE="Times"><P>Four parameters are required to describe a completely general hyperslab. Each parameter is an array whose rank is the same as that of the dataspace:
|
||||
|
||||
<UL>
|
||||
</FONT><CODE><LI>start</CODE>: a starting location for the hyperslab. In the example <CODE>start</CODE> is (1,0).
|
||||
</FONT><CODE><LI>start</CODE>: a starting location for the hyperslab. In the example <CODE>start</CODE> is (0,1).
|
||||
<CODE><LI>stride</CODE>: the number of elements to separate each element or block to be selected. In the example <CODE>stride</CODE><I> </I> is (4,3). If the stride parameter is set to NULL, the stride size defaults to 1 in each dimension.
|
||||
<CODE><LI>count</CODE>: the number of elements or blocks to select along each dimension. In the example, <CODE>count</CODE> is (2,4).
|
||||
<CODE><LI>block</CODE>: the size of the block selected from the dataspace. In the example, <CODE>block</CODE> is (3,2). If the block parameter is set to NULL, the block size defaults to a single element in each dimension, as if the block array was set to all 1s.</UL>
|
||||
|
||||
@ -326,10 +326,9 @@ These tools enable the user to examine HDF5 files interactively.
|
||||
<p>
|
||||
The <code>-h</code> option causes the following
|
||||
syntax summary to be displayed:<br>
|
||||
<dir><code>
|
||||
h5toh4 file.h5 file.hdf<br>
|
||||
h5toh4 file.h5<br>
|
||||
h5toh4 -m file1.h5 file2.h5 ...<br></code></dir>
|
||||
<pre> h5toh4 file.h5 file.hdf
|
||||
h5toh4 file.h5
|
||||
h5toh4 -m file1.h5 file2.h5 ...</pre>
|
||||
|
||||
<p>
|
||||
|
||||
@ -358,6 +357,11 @@ These tools enable the user to examine HDF5 files interactively.
|
||||
be fixed or extendable. The members of the
|
||||
compound datatype are constrained to be no more
|
||||
than rank 4.
|
||||
<li>HDF5 dataset objects of single dimension and fixed length string
|
||||
datatype are converted into HDF4 Vdata objects. The HDF4 Vdata is a
|
||||
single field whose order is the length of the HDF5 string type. The
|
||||
number of records of the Vdata is the length of the single dimension
|
||||
which may be fixed or extendable.
|
||||
</ul>
|
||||
|
||||
Other objects are not converted and are not recorded
|
||||
@ -365,7 +369,7 @@ These tools enable the user to examine HDF5 files interactively.
|
||||
<p>
|
||||
Attributes associated with any of the supported HDF5
|
||||
objects are carried over to the HDF4 objects.
|
||||
Attributes may be of integer or floating point datatype
|
||||
Attributes may be of integer, floating point, or fixed length string datatype
|
||||
and they may have up to 32 fixed dimensions.
|
||||
<p>
|
||||
All datatypes are converted to big-endian.
|
||||
@ -432,7 +436,7 @@ Tools
|
||||
<a href="mailto:hdfhelp@ncsa.uiuc.edu">HDF Help Desk</a>
|
||||
|
||||
<br>
|
||||
Last modified: 30 October 1998
|
||||
Last modified: 29 April 1999
|
||||
|
||||
</body>
|
||||
</html>
|
||||
|
||||
Loading…
Reference in New Issue
Block a user