- Cleaning Up Released Handles
在释放一个句柄之前，务必将这个句柄复制伪NULL （0或则其他默认值）。这样能够保证程序其他地方不会重复使用无效句柄。看看如下代码，如何清除一个Windows ＡＰＩ的文件句柄：
HANDLE hFile = INVALID_HANDLE_VALUE; // Open file hFile = CreateFile(_T("example.dat"), FILE_READ|FILE_WRITE, FILE_OPEN_EXISTING); if(hFile==INVALID_HANDLE_VALUE) { return FALSE; // Error opening file } // Do something with file // Finally, close the handle if(hFile!=INVALID_HANDLE_VALUE) { CloseHandle(hFile); // Close handle to file hFile = INVALID_HANDLE_VALUE; // Clean up handle } 下面代码展示如何清除File *句柄：
// First init file handle pointer with NULL FILE* f = NULL; // Open handle to file errno_t err = _tfopen_s(_T("example.dat"), _T("rb")); if(err!=0 || f==NULL) return FALSE; // Error opening file // Do something with file // When finished, close the handle if(f!=NULL) // Check that handle is valid { fclose(f); f = NULL; // Clean up pointer to handle }
- Using delete [] Operator for Arrays
如果你分配一个单独的对象，可以直接使用new ，同样你释放单个对象的时候,可以直接使用delete . 然而,申请一个对象数组对象的时候可以使用new,但是释放的时候就不能使用delete ,而必须使用delete[]：
// Create an array of objects CVehicle* paVehicles = new CVehicle[10]; delete [] paVehicles; // Free pointer to array paVehicles = NULL; // Set pointer with NULLor // Create a buffer of bytes LPBYTE pBuffer = new BYTE[255]; delete [] pBuffer; // Free pointer to array pBuffer = NULL; // Set pointer with NULL
- Allocating Memory Carefully
有时候，程序需要动态分配一段缓冲区，这个缓冲区是在程序运行的时候决定的。例如、你需要读取一个文件的内容，那么你就需要申请该文件大小的缓冲区来保存该文件的内容。在申请这段内存之前，请注意，malloc() or new是不能申请0字节的内存，如不然，将导致malloc() or new函数调用失败。传递错误的参数给malloc() 函数将导致C运行时错误。如下代码展示如何动态申请内存：
// Determine what buffer to allocate. UINT uBufferSize = GetBufferSize(); LPBYTE* pBuffer = NULL; // Init pointer to buffer // Allocate a buffer only if buffer size > 0 if(uBufferSize>0) pBuffer = new BYTE[uBufferSize];
为了进一步了解如何正确的分配内存，你可以读下这篇文章。
- Using Asserts Carefully
Asserts用语调试模式检测先决条件和后置条件。但当我们编译器处于release模式的时候，Asserts在预编阶段被移除。因此，用Asserts是不能够检测我们的程序状态,错误代码如下：
#include// This function reads a sports car's model from a file CVehicle* ReadVehicleModelFromFile(LPCTSTR szFileName) { CVehicle* pVehicle = NULL; // Pointer to vehicle object // Check preconditions assert(szFileName!=NULL); // This will be removed by preprocessor in Release mode! assert(_tcslen(szFileName)!=0); // This will be removed in Release mode! // Open the file FILE* f = _tfopen(szFileName, _T("rt")); // Create new CVehicle object pVehicle = new CVehicle(); // Read vehicle model from file // Check postcondition assert(pVehicle->GetWheelCount()==4); // This will be removed in Release mode! // Return pointer to the vehicle object return pVehicle; }
看看上述的代码，Asserts能够在debug模式下检测我们的程序,在release 模式下却不能。所以我们还是不得不用if()来这步检测操作。正确的代码如下；
CVehicle* ReadVehicleModelFromFile(LPCTSTR szFileName, ) { CVehicle* pVehicle = NULL; // Pointer to vehicle object // Check preconditions assert(szFileName!=NULL); // This will be removed by preprocessor in Release mode! assert(_tcslen(szFileName)!=0); // This will be removed in Release mode! if(szFileName==NULL || _tcslen(szFileName)==0) return NULL; // Invalid input parameter // Open the file FILE* f = _tfopen(szFileName, _T("rt")); // Create new CVehicle object pVehicle = new CVehicle(); // Read vehicle model from file // Check postcondition assert(pVehicle->GetWheelCount()==4); // This will be removed in Release mode! if(pVehicle->GetWheelCount()!=4) { // Oops... an invalid wheel count was encountered! delete pVehicle; pVehicle = NULL; } // Return pointer to the vehicle object return pVehicle; }
- Checking Return Code of a Function
断定一个函数执行一定成功是一种常见的错误。当你调用一个函数的时候，建议检查下返回代码和返回参数的值。如下代码持续调用Windows API ,程序是否继续执行下去依赖于该函数的返回结果和返回参数值。
HRESULT hres = E_FAIL; IWbemServices *pSvc = NULL; IWbemLocator *pLoc = NULL; hres = CoInitializeSecurity( NULL, -1, // COM authentication NULL, // Authentication services NULL, // Reserved RPC_C_AUTHN_LEVEL_DEFAULT, // Default authentication RPC_C_IMP_LEVEL_IMPERSONATE, // Default Impersonation NULL, // Authentication info EOAC_NONE, // Additional capabilities NULL // Reserved ); if (FAILED(hres)) { // Failed to initialize security if(hres!=RPC_E_TOO_LATE) return FALSE; } hres = CoCreateInstance( CLSID_WbemLocator, 0, CLSCTX_INPROC_SERVER, IID_IWbemLocator, (LPVOID *) &pLoc); if (FAILED(hres) || !pLoc) { // Failed to create IWbemLocator object. return FALSE; } hres = pLoc->ConnectServer( _bstr_t(L"ROOT\\CIMV2"), // Object path of WMI namespace NULL, // User name. NULL = current user NULL, // User password. NULL = current 0, // Locale. NULL indicates current NULL, // Security flags. 0, // Authority (e.g. Kerberos) 0, // Context object &pSvc // pointer to IWbemServices proxy ); if (FAILED(hres) || !pSvc) { // Couldn't conect server if(pLoc) pLoc->Release(); return FALSE; } hres = CoSetProxyBlanket( pSvc, // Indicates the proxy to set RPC_C_AUTHN_WINNT, // RPC_C_AUTHN_xxx RPC_C_AUTHZ_NONE, // RPC_C_AUTHZ_xxx NULL, // Server principal name RPC_C_AUTHN_LEVEL_CALL, // RPC_C_AUTHN_LEVEL_xxx RPC_C_IMP_LEVEL_IMPERSONATE, // RPC_C_IMP_LEVEL_xxx NULL, // client identity EOAC_NONE // proxy capabilities ); if (FAILED(hres)) { // Could not set proxy blanket. if(pSvc) pSvc->Release(); if(pLoc) pLoc->Release(); return FALSE; }