University:
California State University, Northridge
Course:
COMP 410 | Logic Programming
Academic year:

2024
Views:

332

Pages:

18
Author:

Tanner Costa

Chapter 4 Structured Exception Handling 1 OBJECTIVES Upon completion of this chapter, you will be able to:   Describe Windows and Visual C++ Structured Exception Handling (SEH) Use SEH to detect and analyze exceptions   Simplify your code’s response to exceptions and errors   Both user- and system-generated Using exception and termination handlers Protect your code from unexpected exceptions  And properly clean up and terminate your program 2 OVERVIEW Structured Exception Handling (SEH) provides a robust mechanism for applications to respond to unexpected events     Hardware faults Addressing exceptions System errors User generated exceptions SEH assures the ability to free resources  Perform clean-up SEH simplifies program logic 3 PART I Exception Handlers 5 TRY AND EXCEPT BLOCKS __try and __except  Keywords recognized by Visual C++ compiler  Actual keywords are specific to the compiler __try { /* Block of monitored code */ } __except (filter_expression) { /* Exception handling block */ } 6 SEH, BLOCKS, AND FUNCTIONS { DWORD x1; /* Block 1 */ ... _try { /* Block 2 */ DWORD x2; .... x2 = f (x1); .... } _except () { /* SEH 2 */ } } DWORD f (DWORD y) { /* Block f */ DWORD z; z = y / (y - 1); return z / y; } STACK Windows Exception Handler x1 x2 Block 1 Block 2 SEH 2 y z Block f Exception Occurs Execute this SEH 7 FILTER EXPRESSIONS The filter_expression is evaluated after an exception It is a literal constant, expression, or a function call Returns one of three values  EXCEPTION_EXECUTE_HANDLER   EXCEPTION_CONTINUE_SEARCH    Normal case This handler does not process this exception; unwind the stack for the next exception handler EXCEPTION_CONTINUE_EXECUTION Some exceptions cannot be continued, and another exception would occur immediately 8 EXCEPTION CODES (1 of 2) How do you know what exception occurred?  And how do you know what filter expression value to generate? DWORD GetExceptionCode (VOID) The filter function itself cannot call GetExceptionCode, so a common usage is: __except (MyFilter (GetExceptionCode ())) { . . .  } 9 EXCEPTION CODES (2 of 2) An alternative function that returns additional information: LPEXCEPTION_POINTERS GetExceptionInformation (VOID) including information on the virtual address causing an access violation 10 EXCEPTION CODE VALUES (1 of 2) 1. Program violations, including:    EXCEPTION_ACCESS_VIOLATION EXCEPTION_DATATYPE_MISALIGNMENT EXCEPTION_NONCONTINUABLE_EXECUTION 2.. Memory allocation exceptions (See Chapter 4) (HeapAlloc and HeapCreate)  STATUS_NO_MEMORY 11 EXCEPTION CODE VALUES (2 of 2) 3. User-defined exception codes 4. Arithmetic codes, such as:   5. EXCEPTION_INT_DIVIDE_BY_ZERO EXCEPTION_FLT_DIVIDE_BY_ZERO Debugger exceptions — EXCEPTION_BREAKPOINT 12 EXCEPTION CONTROL FLOW _try { . . . i = j / 0; . . . } _except (Filter (GetExceptionCode ())) { . . . } . . . DWORD Filter (DWORD ExCode) { switch (ExCode) { . . . case EXCEPTION_INT_DIVIDE_BY_ZERO: . . . return EXCEPTION_EXECUTE_HANDLER; case . . . } } 1 2 6 7 3 4 5 13 USER-GENERATED EXCEPTIONS (1 of 2) VOID RaiseException (DWORD dwExceptionCode, DWORD dwExceptionFlags, DWORD cArguments, LPDWORD lpArguments) dwExceptionCode bits 31, 30: 0 — Success 1 — Informational 2 — Warning 3 — Error Bit 29: Set Bit 28: 0 Typical value: 0XE0000006 Bits 27–0: User Specified 14 USER-GENERATED EXCEPTIONS (2 of 2) dwExceptionFlags — EXCEPTION_NONCONTINUABLE indicates filter expression should not generate EXCEPTION_CONTINUE_EXECUTION lpArguments — If not NULL, points to an array of cArguments EXCEPTION_MAXIMUM_PARAMETERS == 15 15 ReportException Function (1 of 2) VOID ReportException (LPCTSTR UserMessage, DWORD ExceptionCode) /* ReportException */ /* Extension of ReportError to generate a user exception code rather than terminating. */ /* UserMessage: Message to be displayed ExceptionCode: 0 - Return > 0 - ExitProcess with this code */ { /* Report as a non-fatal error */ if (lstrlen (UserMessage) > 0) ReportError (UserMessage, 0, TRUE); 16 ReportException Function (2 of 2) /* If fatal, raise an exception */ /* Mask out any high order bits in the */ /* user-supplied exception code */ } if (ExceptionCode != 0) RaiseException ( (0x0FFFFFFF & ExceptionCode) | 0xE0000000, 0, 0, NULL); return; 17 ENABLING FLOATING POINT EXCEPTIONS (1 of 2) Skip if you are not interested in floating point arithmetic To enable floating point exceptions, you need to set the fp mask (set the bit off to enable the exception) int iFPMask; /* Save old control mask */ iFPMask = _controlfp (0, 0); iFPMask &= ~(EM_OVERFLOW | EM_UNDERFLOW | EM_INEXACT | EM_ZERODIVIDE | EM_DENORMAL); _controlfp (iFPMask, MCW_EM); /* Set new control mask*/ /* Restore the old mask to disable exceptions */ _controlfp (iFPMask, 0xFFFFFFFF); 18 ENABLING FLOATING POINT EXCEPTIONS (2 of 2) Formula: (current_mask & ~mask) | (new & mask) After a FP exception, clear it with _clearfp() 19

Structured Exception Handling, Part 1

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