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<concept id="GUID-40671EEC-DACC-5F0B-978C-2794FB206E62" xml:lang="en"><title>Types

of error and recovery</title><shortdesc>Describes error conditions and how errors are handled.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>Error conditions can be divided into three broad categories:</p>

<ul>

<li id="GUID-5E06C730-C4DC-5E09-A7F1-8101BC8B6AFC"><p>program errors, such

as an attempt to access an element beyond the bounds of an array or buffer</p> </li>

<li id="GUID-DFCB0C57-A2BB-55DF-BA2A-FC0D5D3C9F45"><p>environment errors,

such as insufficient memory, insufficient disk space, or other missing resources</p> </li>

<li id="GUID-AD65EABD-573A-5A03-B59B-50A1DE7219DF"><p>user errors, such as

an attempt to enter bad data in a dialog, an invalid action in, say, a word

processor, or bad syntax in a source file</p> </li>

</ul>

<p>Program errors are checked by asserts (<codeph>__ASSERT_DEBUG</codeph> macro),

and are signalled by a panic. Recovery from such errors involves re-writing

part of the program that contained the error. </p>

<p>Environment and user errors can be handled in broadly two ways:</p>

<ul>

<li id="GUID-7DAF8642-F413-5332-958C-A7B31C1BDD1F"><p>If they can be detected

before an action is performed, then a return value other than <codeph>KErrNone</codeph> is

a convenient means to signal the error.</p> <p>This method is simple to program,

and cleanup requirements, if they exist at all, are often easy to identify

and handle.</p> </li>

<li id="GUID-4561F90D-E7C0-5D5C-AB33-4F2C25D7C4F1"><p>Alternatively, the program

can use the exception handling and cleanup techniques discussed in this section.</p> <p>This

method is more appropriate when the detection of an error occurs deep inside

the processing of a requested action: if the error return value method were

used, every function would have to return such an error and cleanup requirements

would have to be handled for virtually every function call. The logic becomes

repetitive and it’s easier to incorporate it into an exception-handling scheme.</p> </li>

</ul>

<p>When programming for possible environment or user error conditions, bear

in mind both approaches for handling them, and choose the most suitable one.</p>

<p>Applications must perform proper cleanup when an exception occurs, because

they are designed to run for long periods (months or even years) without interruption

or system re-boot. </p>