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    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

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

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

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

    15 <ul>

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

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

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

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

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

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

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

    23 </ul>

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

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

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

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

    28 <ul>

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

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

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

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

    33 and handle.</p> </li>

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

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

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

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

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

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

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

    41 </ul>

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

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

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

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

    46 or system re-boot. </p>

    47 </conbody></concept>