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      1 /*
      2 *******************************************************************************
      3 *
      4 *   Copyright (C) 2009-2011, International Business Machines
      5 *   Corporation and others.  All Rights Reserved.
      6 *
      7 *******************************************************************************
      8 *   file name:  errorcode.h
      9 *   encoding:   US-ASCII
     10 *   tab size:   8 (not used)
     11 *   indentation:4
     12 *
     13 *   created on: 2009mar10
     14 *   created by: Markus W. Scherer
     15 */
     16 
     17 #ifndef __ERRORCODE_H__
     18 #define __ERRORCODE_H__
     19 
     20 /**
     21  * \file
     22  * \brief C++ API: ErrorCode class intended to make it easier to use
     23  *                 ICU C and C++ APIs from C++ user code.
     24  */
     25 
     26 #include "unicode/utypes.h"
     27 #include "unicode/uobject.h"
     28 
     29 U_NAMESPACE_BEGIN
     30 
     31 /**
     32  * Wrapper class for UErrorCode, with conversion operators for direct use
     33  * in ICU C and C++ APIs.
     34  * Intended to be used as a base class, where a subclass overrides
     35  * the handleFailure() function so that it throws an exception,
     36  * does an assert(), logs an error, etc.
     37  * This is not an abstract base class. This class can be used and instantiated
     38  * by itself, although it will be more useful when subclassed.
     39  *
     40  * Features:
     41  * - The constructor initializes the internal UErrorCode to U_ZERO_ERROR,
     42  *   removing one common source of errors.
     43  * - Same use in C APIs taking a UErrorCode * (pointer)
     44  *   and C++ taking UErrorCode & (reference) via conversion operators.
     45  * - Possible automatic checking for success when it goes out of scope.
     46  *
     47  * Note: For automatic checking for success in the destructor, a subclass
     48  * must implement such logic in its own destructor because the base class
     49  * destructor cannot call a subclass function (like handleFailure()).
     50  * The ErrorCode base class destructor does nothing.
     51  *
     52  * Note also: While it is possible for a destructor to throw an exception,
     53  * it is generally unsafe to do so. This means that in a subclass the destructor
     54  * and the handleFailure() function may need to take different actions.
     55  *
     56  * Sample code:
     57  * \code
     58  *   class IcuErrorCode: public icu::ErrorCode {
     59  *   public:
     60  *     virtual ~IcuErrorCode() {  // should be defined in .cpp as "key function"
     61  *       // Safe because our handleFailure() does not throw exceptions.
     62  *       if(isFailure()) { handleFailure(); }
     63  *     }
     64  *   protected:
     65  *     virtual void handleFailure() const {
     66  *       log_failure(u_errorName(errorCode));
     67  *       exit(errorCode);
     68  *     }
     69  *   };
     70  *   IcuErrorCode error_code;
     71  *   UConverter *cnv = ucnv_open("Shift-JIS", error_code);
     72  *   length = ucnv_fromUChars(dest, capacity, src, length, error_code);
     73  *   ucnv_close(cnv);
     74  *   // IcuErrorCode destructor checks for success.
     75  * \endcode
     76  *
     77  * @stable ICU 4.2
     78  */
     79 class U_COMMON_API ErrorCode: public UMemory {
     80 public:
     81     /**
     82      * Default constructor. Initializes its UErrorCode to U_ZERO_ERROR.
     83      * @stable ICU 4.2
     84      */
     85     ErrorCode() : errorCode(U_ZERO_ERROR) {}
     86     /** Destructor, does nothing. See class documentation for details. @stable ICU 4.2 */
     87     virtual ~ErrorCode();
     88     /** Conversion operator, returns a reference. @stable ICU 4.2 */
     89     operator UErrorCode & () { return errorCode; }
     90     /** Conversion operator, returns a pointer. @stable ICU 4.2 */
     91     operator UErrorCode * () { return &errorCode; }
     92     /** Tests for U_SUCCESS(). @stable ICU 4.2 */
     93     UBool isSuccess() const { return U_SUCCESS(errorCode); }
     94     /** Tests for U_FAILURE(). @stable ICU 4.2 */
     95     UBool isFailure() const { return U_FAILURE(errorCode); }
     96     /** Returns the UErrorCode value. @stable ICU 4.2 */
     97     UErrorCode get() const { return errorCode; }
     98     /** Sets the UErrorCode value. @stable ICU 4.2 */
     99     void set(UErrorCode value) { errorCode=value; }
    100     /** Returns the UErrorCode value and resets it to U_ZERO_ERROR. @stable ICU 4.2 */
    101     UErrorCode reset();
    102     /**
    103      * Asserts isSuccess().
    104      * In other words, this method checks for a failure code,
    105      * and the base class handles it like this:
    106      * \code
    107      *   if(isFailure()) { handleFailure(); }
    108      * \endcode
    109      * @stable ICU 4.4
    110      */
    111     void assertSuccess() const;
    112     /**
    113      * Return a string for the UErrorCode value.
    114      * The string will be the same as the name of the error code constant
    115      * in the UErrorCode enum.
    116      * @stable ICU 4.4
    117      */
    118     const char* errorName() const;
    119 
    120 protected:
    121     /**
    122      * Internal UErrorCode, accessible to subclasses.
    123      * @stable ICU 4.2
    124      */
    125     UErrorCode errorCode;
    126     /**
    127      * Called by assertSuccess() if isFailure() is true.
    128      * A subclass should override this function to deal with a failure code:
    129      * Throw an exception, log an error, terminate the program, or similar.
    130      * @stable ICU 4.2
    131      */
    132     virtual void handleFailure() const {}
    133 };
    134 
    135 U_NAMESPACE_END
    136 
    137 #endif  // __ERRORCODE_H__
    138