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<concept id="GUID-261ADCEC-C8C8-46E3-A7DC-804AC868C233" xml:lang="en"><title>Descriptors</title><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>Descriptors are self-describing strings that can be used to store binary
data and text. Each descriptor object holds the length of the string as well
as its type which identifies the underlying memory layout of the data it holds.
For more information on different descriptor classes, see <xref href="GUID-11EEFB3D-0414-5BEB-9D78-56A4B9154008.dita">Using
Descriptors</xref>.</p>
<p>There are modifiable and non-modifiable descriptors, the latter type
is identified by a "C" suffix in the class name. The length of a non-modifiable
descriptor is defined when compiling an application, and the length of a modifiable
descriptor can vary within the limits set by <codeph>iMaxLength</codeph>.
Nonmodifiable descriptors are more secure, as their length is checked during
compilation. The following figure shows the differences between these types.</p>
<fig id="GUID-A8F9937F-25A6-4E80-845F-35994B7E13E5"><title>Differences between modifiable, nonmodifiable, and pointer descriptors</title><image href="GUID-40619192-8C2F-4267-BFCA-F53E10BF5A31_d0e12841_href.png"/></fig>
<p>When designing applications, avoid using fixed-length buffers as parameters
and use base classes (preferably constant base type <codeph><xref href="jar:GUID-35228542-8C95-4849-A73F-2B4F082F0C44.jar!/sdk/doc_source/reference/reference-cpp/Kernel_Architecture_2/e32cmn.hGlobals.html#%3a%3aTDesC" format="application/java-archive">TDesC</xref></codeph>)
instead. Descriptor objects provide a flexible interface for manipulating
the contained string, including size and length checks. Take advantage of
these when possible.</p>
<p>For more information and examples, see the <xref href="GUID-0817AD1D-58CF-5108-ACBF-26DFD4BA395E.dita">Descriptors
Overview</xref> topic.</p>
</conbody></concept>