写入位置 时发生访问冲突

class CRequest : public CObject

{
public:
int StuffString( const CString& strData );
void StuffHead(CString method, CString lpszURL);
CRequest();
virtual ~CRequest();
CByteArray m_buf;
CString m_strLine;
int m_cbOut;
};
.........................
CRequest::CRequest()
{
m_buf.SetSize( 1024 );
m_cbOut = 0;
}

CRequest::~CRequest()
{

}
.........................
.........................

CRequest* m_pReq;    

if (m_pReq != NULL)
{
    m_pReq->m_cbOut=0;  //发声访问冲突
}

这里      m_pReq->m_cbOut=0;  //发声访问冲突

m_pReq虽然不是null但是指向无效的地址，比如指针没有初始化或者被释放。