[英]C++ Pointers, Unable To Read Memory
為什么,當我初始化指針時,我可以讀取分配的值:
DWORD *pBytesReturned = new DWORD[0];
_result = EnumProcesses(pProcessIds, 1000, pBytesReturned);
但是當我這樣初始化它時,我無法讀取分配的值:
DWORD *pBytesReturned = 0;
_result = EnumProcesses(pProcessIds, 1000, pBytesReturned);
如果需要,這是完整的代碼:
#include "stdafx.h"
#include <Psapi.h>
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR pCmdLine, int iCmdShow)
{
bool _result;
DWORD *pProcessIds = new DWORD[1000];
DWORD cb;
DWORD *pBytesReturned =0;
_result = EnumProcesses(pProcessIds, 1000, pBytesReturned);
}
功能的意圖
BOOL
WINAPI
EnumProcesses (
_Out_writes_bytes_(cb) DWORD * lpidProcess,
_In_ DWORD cb,
_Out_ LPDWORD lpcbNeeded
);
將指針作為第三個參數,並且該指針必須指向函數將在其中存儲雙字的有效內存位置。 預期的函數調用應如下所示
DWORD *pProcessIds = new DWORD[1000];
DWORD bytesReturned = 0;
bool _result = EnumProcesses(pProcessIds, 1000, &bytesReturned);
或像這樣
DWORD *pProcessIds = new DWORD[1000];
DWORD *pBytesReturned = new DWORD[1];
bool _result = EnumProcesses(pProcessIds, 1000, pBytesReturned);
但您不應該使用NULL指針,並且希望調試器取消引用它。
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