《Windows核心编程》读书笔记二十四章异常处理程序与软件异常

DWORD Funcmeister2() {DWORD dwTemp &＃61; 0;// 1. Do any processing here.//...__try {// 2. Perform some operation.dwTemp &＃61; 5 / dwTemp; // Generates an exceptiondwTemp &＃43;&＃61; 10; // Never executes}__except (/* 3. Evaluate filter. */EXCEPTION_EXECUTE_HANDLER) {// 4. Handle an exception;MessageBeep(0);// ...}// 5. Continue processing.return dwTemp;
}
除零错误会被cpu捕获并抛出一个硬件异常。接着系统定位到except块&＃xff0c;并对异常过滤程序的表达式求值。

char* RobustStrCpy(char* strDes, const char* src) {__try {strcpy(strDes, src);}__except (EXCEPTION_EXECUTE_HANDLER) {// Nothing to do here.}return strDes;
}以上代码虽然捕获了异常但是没有做任何处理。这是不可取的。可能会导致隐患和后续问题。

int RobustHowManyToken(const char * str) {int nHowManyTokens &＃61; -1; // -1 indicates failurechar * strTemp &＃61; NULL; // Assume failure__try {// Allocate a temporary bufferstrTemp &＃61; (char*)malloc(strlen(str) &＃43; 1);// Copy the original string to the temporary bufferstrcpy(strTemp, str);// Get the first tokenchar * pszToken &＃61; strtok(strTemp, " ");// Iterate through all the tokensfor (; pszToken !&＃61; NULL; pszToken &＃61; strtok(NULL, " "))nHowManyTokens&＃43;&＃43;;nHowManyTokens&＃43;&＃43;; // Add 1 since we started at -1}__except (EXCEPTION_EXECUTE_HANDLER) {// Nothing to do here}// Free the temporary buffer (guaranteed)free(strTemp);return (nHowManyTokens);
}
能过处理常见的内存错误。

PBYTE RobustMemDup(PBYTE pbSrc, size_t cb) {PBYTE pbDup &＃61; NULL; // Assume failure__try {// Allocate a buffer for the duplicate memory blockpbDup &＃61; (PBYTE)malloc(cb);memcpy(pbDup, pbSrc, cb);}__except (EXCEPTION_EXECUTE_HANDLER) {free(pbDup);pbDup &＃61; NULL;}return pbDup;
}

void FuncOStimpy1() {// 1. Do any processing here.// ...__try{// 2. Call another function.FuncORen1();// Code here never executes.}__except (/* 6. Evaluate filter. */ EXCEPTION_EXECUTE_HANDLER){// 8. Afte rthe unwind, the exception handler executes.MessageBox(...);}// 9. Exception handled -- continue execution.
}void FuncORen1() {DWORD dwTemp &＃61; 0;// 3. Do any processing here.__try{// 4. Request permission to access protected data.WaitForSingleObject(g_hSem, INFINITE);// 5. Modify the data.// An exception is generated here.g_dwProtectedData &＃61; 5 / dwTemp;}__finally {// 7. Global unwind occurs because filter evaluated// to EXCEPTION_EXECUTE_HANDLER.// Allow others to use protected data.ReleaseSemaphore(g_hSem, 1, NULL);}// Continue processing -- never executes.
}代码的执行顺序参考注释。

void FuncMonkey(){__try{FuncFish();}__except (EXCEPTION_EXECUTE_HANDLER) {MessageBeep(0);}
}void FuncFish() {FuncPheasant();MessageBox(NULL, TEXT("FuncFish"), TEXT(""), MB_OK);
}void FuncPheasant() {__try{strcpy(NULL, NULL);}__finally{return;}
}

1>------ Build started: Project: SubProcess, Configuration: Debug Win32 ------
1> SubProcess.cpp
1>c:\users\admin\documents\visual studio 2013\projects\consoleapplication3\subprocess\subprocess.cpp(41): error C4532: &＃39;return&＃39; : jump out of __finally block has undefined behavior during termination handling
&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61; Build: 0 succeeded, 1 failed, 2 up-to-date, 0 skipped &＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;

24.3 EXCEPTION_CONTINUE_EXECUTION

TCHAR g_szBuffer[100];
LONG OilFilter1(TCHAR ** ppchBuffer);void FunclinRoosevelt1() {int x &＃61; 0;TCHAR *pchBuffer &＃61; NULL;__try{*pchBuffer &＃61; TEXT(&＃39;J&＃39;);x &＃61; 5 / x;}__except (OilFilter1(&pchBuffer)) {MessageBox(NULL, TEXT("An exception occured"), NULL, MB_OK);}MessageBox(NULL, TEXT("Function completed"), NULL, MB_OK);
}LONG OilFilter1(TCHAR **ppchBuffer) {if (*ppchBuffer &＃61;&＃61; NULL) {*ppchBuffer &＃61; g_szBuffer;return EXCEPTION_CONTINUE_EXECUTION;}return EXCEPTION_EXECUTE_HANDLER;
}
1&＃xff09;第一次给pchBuffer地址赋值会触发异常&＃xff08;访问NULL地址&＃xff09;&＃xff0c;过滤函数中判断出了异常是由于给空地址赋值。

TCHAR g_szBuffer[100];
LONG OilFilter3(TCHAR ** ppchBuffer);void FuncAtude3(TCHAR * sz) {__try{*sz &＃61; TEXT(&＃39;\0&＃39;);}__except (EXCEPTION_CONTINUE_SEARCH) {// This never executes.}
}
void FunclinRoosevelt3() {int x &＃61; 0;TCHAR *pchBuffer &＃61; NULL;__try{FuncAtude3(pchBuffer);}__except (OilFilter3(&pchBuffer)) {MessageBox(NULL, TEXT("An exception occured"), NULL, MB_OK);}MessageBox(NULL, TEXT("Function completed"), NULL, MB_OK);
}

1)在FuncAtude3中试图写入NULL地址会引发异常。

int x, y;__try{x &＃61; 0;y &＃61; 4 / x;}__except ((GetExceptionCode() &＃61;&＃61; EXCEPTION_INT_DIVIDE_BY_ZERO) ?EXCEPTION_EXECUTE_HANDLER : EXCEPTION_CONTINUE_SEARCH) {// Handle divide by zero exception.}

int x, y;__try{x &＃61; 0;y &＃61; 4 / x;}__except ((GetExceptionCode() &＃61;&＃61; EXCEPTION_INT_DIVIDE_BY_ZERO) ?EXCEPTION_EXECUTE_HANDLER : EXCEPTION_CONTINUE_SEARCH) { switch (GetExceptionCode()) {case EXCEPTION_INT_DIVIDE_BY_ZERO:// Handle divide by zero exception.break;}}
但是不能在过滤函数内部调用GetExceptionCode()

LONG CoffeeFilter(){// Compilation error: illegal call to GetExceptionCode.return (GetExceptionCode() &＃61;&＃61; EXCEPTION_INT_DIVIDE_BY_ZERO) ?EXCEPTION_EXECUTE_HANDLER : EXCEPTION_CONTINUE_SEARCH;
}int _tmain(int argc, TCHAR* argv[], TCHAR * env[])
{int x, y;__try{x &＃61; 0;y &＃61; 4 / x;}__except (CoffeeFilter()){}return 0;
}改写过的异常过滤函数

LONG CoffeeFilter(DWORD dwExceptionCode){// Compilation error: illegal call to GetExceptionCode.return (dwExceptionCode &＃61;&＃61; EXCEPTION_INT_DIVIDE_BY_ZERO) ?EXCEPTION_EXECUTE_HANDLER : EXCEPTION_CONTINUE_SEARCH;
}int _tmain(int argc, TCHAR* argv[], TCHAR * env[])
{int x, y;__try{x &＃61; 0;y &＃61; 4 / x;}__except (CoffeeFilter(GetExceptionCode())){}return 0;
}

typedef struct _EXCEPTION_POINTERS {PEXCEPTION_RECORD ExceptionRecord;PCONTEXT ContextRecord;
} EXCEPTION_POINTERS, *PEXCEPTION_POINTERS;

void FuncSkunk() {// Declare variables that we can use to save the exception// record and the context if an exception should occur.EXCEPTION_RECORD SavedExceptRec;CONTEXT SavedContext;__try{// ...}__except (SavedExceptRec &＃61; *(GetExceptionInformation())->ExceptionRecord,SavedContext &＃61;*(GetExceptionInformation())->ContextRecord,EXCEPTION_EXECUTE_HANDLER) {// We can use the SavedExceptRec and SavedContext// variables inside the handler code block.switch (SavedExceptRec.ExceptionCode) {//...}}
}
注意逗号表达式&＃xff0c;最终的值是最右边的表达式&＃xff0c;前面的表达式会被计算执行。

typedef struct _EXCEPTION_RECORD {DWORD ExceptionCode;DWORD ExceptionFlags;struct _EXCEPTION_RECORD *ExceptionRecord;PVOID ExceptionAddress;DWORD NumberParameters;ULONG_PTR ExceptionInformation[EXCEPTION_MAXIMUM_PARAMETERS];} EXCEPTION_RECORD;

LONG ExpFltr(LPEXCEPTION_POINTERS pep) {TCHAR szBuf[300], *p;PEXCEPTION_RECORD pER &＃61; pep->ExceptionRecord;DWORD dwExceptionCode &＃61; pER->ExceptionCode;StringCchPrintf(szBuf, _countof(szBuf),TEXT("Code &＃61; %x, Address &＃61; %p"),dwExceptionCode, pER->ExceptionAddress);// Find the end of the string.p &＃61; _tcschr(szBuf, TEXT(&＃39;\0&＃39;));// I used a switch statement in case Microsoft adds// information for other exception codes in the future.switch (dwExceptionCode) {case EXCEPTION_ACCESS_VIOLATION:StringCchPrintf(p, _countof(szBuf),TEXT("\n--> Attempt to %s data at address %p"),pER->ExceptionInformation[0] ?TEXT("write") : TEXT("read"),pER->ExceptionInformation[1]);break;default:break;}MessageBox(NULL, szBuf, TEXT("Exception"),MB_OK | MB_ICONEXCLAMATION);return EXCEPTION_CONTINUE_SEARCH;
}
例如一下测试代码

int _tmain(int argc, TCHAR* argv[], TCHAR * env[])
{__try{// ...// ...char * p &＃61; (char *)0xffffffff;char a &＃61; *p;}__except (ExpFltr(GetExceptionInformation())) {// ...}return 0;
}
运行结果&＃xff1a;

WINBASEAPI
__analysis_noreturn
VOID
WINAPI
RaiseException(_In_ DWORD dwExceptionCode,_In_ DWORD dwExceptionFlags,_In_ DWORD nNumberOfArguments,_In_reads_opt_(nNumberOfArguments) CONST ULONG_PTR * lpArguments);第一个参数是dwExceptionCode是抛出异常的标识符ID。