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diff --git a/doc/html/Datatypes.html b/doc/html/Datatypes.html index e02a7f7..604b480 100644 --- a/doc/html/Datatypes.html +++ b/doc/html/Datatypes.html @@ -4,7 +4,69 @@ <title>The Data Type Interface (H5T)</title> </head> - <body> + <body bgcolor="#FFFFFF"> + + +<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> + + <h1>The Data Type Interface (H5T)</h1> <h2>1. Introduction</h2> @@ -358,9 +420,6 @@ <em>19971205162530</em>; as an integer value in Unix time(2) format; or other variations. - <p>I'm deferring definition until later since they're probably not - as important as the other data types. - <h3>3.4. Properties of Character String Atomic Types</h3> <p>Fixed-length character string types are used to store textual @@ -437,6 +496,88 @@ but the application is responsible for data conversion of these types. + <h3>3.7 Character and String Datatype Issues</h3> + + The <code>H5T_NATIVE_CHAR</code> and <code>H5T_NATIVE_UCHAR</code> + data types are actually numeric data (1-byte integers). If the + application wishes to store character data, then an HDF5 + <em>string</em> data type should be derived from + <code>H5T_C_S1</code> instead. + + <h4>Motivation</h4> + + HDF5 defines at least three classes of data types: + integer data, floating point data, and character data. + However, the C language defines only integer and + floating point data types; character data in C is + overloaded on the 8- or 16-bit integer types and + character strings are overloaded on arrays of those + integer types which, by convention, are terminated with + a zero element. + + In C, the variable <code>unsigned char s[256]</code> is + either an array of numeric data, a single character string + with at most 255 characters, or an array of 256 characters, + depending entirely on usage. For uniformity with the + other <code>H5T_NATIVE_</code> types, HDF5 uses the + numeric interpretation of <code>H5T_NATIVE_CHAR</code> + and <code>H5T_NATIVE_UCHAR</code>. + + + <h4>Usage</h4> + + To store <code>unsigned char s[256]</code> data as an + array of integer values, use the HDF5 data type + <code>H5T_NATIVE_UCHAR</code> and a data space that + describes the 256-element array. Some other application + that reads the data will then be able to read, say, a + 256-element array of 2-byte integers and HDF5 will + perform the numeric translation. + + To store <code>unsigned char s[256]</code> data as a + character string, derive a fixed length string data type + from <code>H5T_C_S1</code> by increasing its size to + 256 characters. Some other application that reads the + data will be able to read, say, a space padded string + of 16-bit characters and HDF5 will perform the character + and padding translations. + + <pre> + hid_t s256 = H5Tcopy(H5T_C_S1); + H5Tset_size(s256, 256); + </pre> + + To store <code>unsigned char s[256]</code> data as + an array of 256 ASCII characters, use an + HDF5 data space to describe the array and derive a + one-character string type from <code>H5T_C_S1</code>. + Some other application will be able to read a subset + of the array as 16-bit characters and HDF5 will + perform the character translations. + The <code>H5T_STR_NULLPAD</code> is necessary because + if <code>H5T_STR_NULLTERM</code> were used + (the default) then the single character of storage + would be for the null terminator and no useful data + would actually be stored (unless the length were + incremented to more than one character). + + <pre> + hid_t s1 = H5Tcopy(H5T_C_S1); + H5Tset_strpad(s1, H5T_STR_NULLPAD); + </pre> + + <h4>Summary</h4> + + The C language uses the term <code>char</code> to + represent one-byte numeric data and does not make + character strings a first-class data type. + HDF5 makes a distinction between integer and + character data and maps the C <code>signed char</code> + (<code>H5T_NATIVE_CHAR</code>) and + <code>unsigned char</code> (<code>H5T_NATIVE_UCHAR</code>) + data types to the HDF5 integer type class. + + <h2>4. Properties of Compound Types</h2> <p>A compound data type is similar to a <code>struct</code> in C @@ -1412,15 +1553,77 @@ H5Tregister(H5T_PERS_SOFT, "cus2be", conversion path whether that conversion path was actually used or not. - - <hr> - <address> - <a href="mailto:hdfhelp@ncsa.uiuc.edu">HDF Help Desk</a> - </address> +<<<<<<< Datatypes.html + + +<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: Wed Dec 16 13:04:58 EST 1998 <!-- hhmts end --> - - </body> + + +</body> </html> |