大家好怎样读取blob类型的数据 MYSQL 中

[greatesun]

大家好怎样读取blob类型的数据

[AkiraChing]

HGLOBAL hgImageMem = NULL;
LPVOID lpvImageMem = NULL;

long lImageSize = rs->GetFields()->GetItem("图片")->ActualSize;

if(lImageSize > 0)
{
_variant_t varImage;
varImage = rs->GetFields()->GetItem("图片")->GetChunk(lImageSize);
if(varImage.vt == (VT_ARRAY | VT_UI1))
{

hgImageMem = GlobalAlloc(GHND, lImageSize);
if(hgImageMem!=NULL)
{
lpvImageMem = GlobalLock( hgImageMem);
char *pBuffer= NULL;
SafeArrayAccessData(varImage.parray,(void **)&pBuffer);
CopyMemory(lpvImageMem,pBuffer,lImageSize);
SafeArrayUnaccessData (varImage.parray);
CFile file("a.jpg",CFile::modeWrite|CFile::modeCreate);
file.Write(lpvImageMem,lImageSize);
file.Close();
}
}
}

GlobalUnlock(hgImageMem);
lpvImageMem=NULL;
GlobalFree(hgImageMem);

[AkiraChing]

从数据库中读取到richedit

_bstr_t bstrConn="Provider=Microsoft.Jet.OLEDB.4.0;"
"Data Source=E:\\vc\\test.mdb;"
"User Id=Admin;Password=;";

_RecordsetPtr rs=NULL;
long lLength=0L;
_variant_t varText;

try
{
rs.CreateInstance(__uuidof(Recordset));
rs->Open("[longText]",bstrConn, adOpenKeyset, adLockOptimistic, adCmdTable);
if(!rs->GetBOF())
rs->MoveFirst();
lLength= rs->GetFields()->GetItem("text")->ActualSize;
LPTSTR pszBuffer= NULL;
varText = rs->GetFields()->GetItem("text")->GetChunk(lLength);
if(varText.vt == (VT_ARRAY | VT_UI1))
{
SafeArrayAccessData(varText.parray,(void **)&pszBuffer);
CopyMemory(m_strRichedit.GetBufferSetLength(lLength),pszBuffer,lLength);
SafeArrayUnaccessData (varText.parray);
}

}
catch (_com_error e)
{
PrintComError(e);
}
rs->Close();
UpdateData(FALSE);

[bluebohe]

11. 访问长数据
在Microsoft SQL中的长数据包括text、image等这样长类型的数据，作为二进制字节来对待。
可以用Field对象的GetChunk和AppendChunk方法来访问。每次可以读出或写入全部数据的一部分，它会记住上次访问的位置。但是如果中间访问了别的字段后，就又得从头来了。
请看下面的例子：
//写入一张照片到数据库：
VARIANT varChunk;
SAFEARRAY *psa;
SAFEARRAYBOUND rgsabound[1];

//VT_ARRAY | VT_UI1
CFile f("h:\\aaa.jpg",CFile::modeRead);
BYTE bVal[ChunkSize+1];
UINT uIsRead=0;
//Create a safe array to store the array of BYTES
while(1)
{
uIsRead=f.Read(bVal,ChunkSize);
if(uIsRead==0)break;
rgsabound[0].cElements =uIsRead;
rgsabound[0].lLbound = 0;
psa = SafeArrayCreate(VT_UI1,1,rgsabound);
for(long index=0;index<uIsRead;index++)
{
if(FAILED(SafeArrayPutElement(psa,&index,&bVal[index])))
::MessageBox(NULL,"啊，又出毛病了。","提示",MB_OK | MB_ICONWARNING);
}
varChunk.vt = VT_ARRAY|VT_UI1;
varChunk.parray = psa;
try{
m_pRecordset->Fields->GetItem("photo")->AppendChunk(varChunk);
}
catch (_com_error &e)
{
CString str=(char*)e.Description();
::MessageBox(NULL,str+"\n又出毛病了。","提示",MB_OK | MB_ICONWARNING);
}
::VariantClear(&varChunk);
::SafeArrayDestroyData( psa);
if(uIsRead<ChunkSize)break;
}//while(1)
f.Close();

//从数据库读一张照片：
CFile f;
f.Open("h:\\bbb.jpg",CFile::modeWrite|CFile::modeCreate);
long lPhotoSize = m_pRecordset->Fields->Item["photo"]->ActualSize;
long lIsRead=0;

_variant_t varChunk;
BYTE buf[ChunkSize];
while(lPhotoSize>0)
{
lIsRead=lPhotoSize>=ChunkSize? ChunkSize:lPhotoSize;
varChunk = m_pRecordset->Fields->
Item["photo"]->GetChunk(lIsRead);
for(long index=0;index<lIsRead;index++)
{
::SafeArrayGetElement(varChunk.parray,&index,buf+index);
}
f.Write(buf,lIsRead);
lPhotoSize-=lIsRead;
}//while()
f.Close();