如何使用oracle ODBC获取BLOB数据 [英] How to get BLOB data using oracle ODBC
问题描述
我试图获取存储在BLOB中的图像,然后将其保存为jpg。
I'm trying to get image that are stored in BLOB and then save it as jpg.
这里我检索二进制数据并将其保存在str
Here i retrieve the binary data and save it in str;
string str;
SQLCHAR buf[500] = {0};
while ((SQL_SUCCEEDED(SQLGetData(StmtHandle, colnum, SQL_C_BINARY, buf, sizeof(buf), NULL))))
{
string data(reinterpret_cast< const char* >(buf), reinterpret_cast< const char* >(buf) + sizeof(buf));
str = str + data;
}
然后将其写入文件
ofstream file;
file.open("C:\\Users\\tom\\Desktop\\img.jpeg");
file << str;
file.close();
我得到不正确的图像。
and i get the incorrect image.
这种数据提取方法有什么问题(我使用 this )?
What's wrong with this method of data extraction (i used this) ?
推荐答案
不熟悉ODBC编程,但一见钟情,我可以看到的一个问题是,你假设你的数据长度是你的缓冲区大小的倍数。但是最后一次读取并不能保证能够准确地返回 500字节的数据。
I'm not familiar with ODBC programming, but at first sight, one issue I can see is that you assume your data length is multiple of your buffer size. But the last read is not guaranteed to return exactly 500 bytes of data.
你应该这样写。也许:
string str;
SQLCHAR buf[500];
SQLLEN cbLeft; // #bytes remained
while ((SQL_SUCCEEDED(SQLGetData(StmtHandle,
colnum,
SQL_C_BINARY,
buf,
sizeof(buf),
&cbLeft))))
// ^^^^^^^
{
string data(reinterpret_cast< const char* >(buf),
reinterpret_cast< const char* >(buf)
+ cbLeft);
// ^^^^^^
str = str + data;
请花几分钟时间查看使用长度/指标值,以检查长度/指标值。
Please take a few minutes to review Using Length/Indicator Values in order to check how the length/indicator value is used.
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