mediumblob存图像数据的问题

[一点也不酷]

用的opencv的库采集的图像，存到MYSQL里面的一个mediumblob里面，代码执行有时候成功有时候失败，失败的时候mysql错误显示语法错误，搞了半天不知道什么原因，盼大神帮忙分析下
代码如下
IplImage* m_Frame;
m_Frame=cvQueryFrame(capture);
long nSize = m_Frame->imageSize;
char* pBuf = m_Frame->imageData;

char* pToDes = new char[nSize*2+1];

long lDestSize = mysql_real_escape_string(theApp.mysql.GetMysql(), pToDes, pBuf, nSize);

char* cQuery = new char[nSize*2+100];
int sql_len = sprintf(cQuery,"update staffphoto set photo = \'%s\' where code = 1",pToDes);
string strQuery = cQuery;

if( theApp.mysql.MysqlEx(strQuery) )
{
string strError = theApp.mysql.OutErrors();
GetDlgItem(IDC_STAFFREG_MES_EDIT)->SetWindowText(_T("读取數據失敗！"));
delete []pToDes;
delete []cQuery;
return;
}

theApp.mysql.FreeRecord();

delete []pToDes;
delete []cQuery;

[道玄希言]

MediumBlob 最大 16M