<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_d0e12633_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>