cv::mat 保存sqlite数据库，使用qt

此文转载自：https://blog.csdn.net/wuyin970303/article/details/113183551#commentBox

• 环境：

1. qt
2. opencv
3. sqlite

• 使用QByteArray::fromRawData()讲Mat数据转换为ByteArray，但这个函数不会保存Mat的长，宽，和类型，需要创建一个stream分别保存。

• 此方法可以将任意cv::mat进行保存和加载

#include<opencv2/opencv.hpp>
#include<QDataStream>
#include<QSqlQuery>


// save sift into database with id
bool Database::addSift(int id, const cv::Mat &sift)
{
    // set id if not exists
    Database::setID(id);

    // create a bytearray to accept the stream
    QByteArray data;  // = QByteArray((const char *)&sift, sizeof(sift));
    QDataStream stream(&data, QIODevice::WriteOnly);
    
    stream << sift.type(); // cv::Mat type
    stream << sift.rows; // cv::Mat rows
    stream << sift.cols; // cv::Mat cols
	
	// calculate the data size of this matrix
    const size_t data_size = sift.cols * sift.rows * sift.elemSize();
	// save all data into stream.
	// this part will not include the format and shape of the matrix
    QByteArray siftByte = QByteArray::fromRawData( (const char*)sift.ptr(), data_size );

    stream << siftByte;

    // insert into database mytable
    QSqlQuery query(db);
    query.prepare("UPDATE mytable SET sift=:sift WHERE id=:id;");
    query.bindValue(":id", id);
    query.bindValue(":sift", data);

    if(!query.exec()) {
        qDebug() << "ERROR: addSift" << query.lastError().text();
        return false;
    } else {
        return true;
    }
}


// load sift mat from database
cv::Mat Database::getSift(int id)
{
    // get data from database mytable
    QSqlQuery query(db);
    query.prepare("SELECT sift FROM mytable WHERE id = :id;");
    query.bindValue(":id", id);
    if(!query.exec()) {
        qDebug() << "ERROR: getSift" << query.lastError().text();
        std::abort();
    } else {
        query.next();
        QByteArray data = query.value(0).toByteArray();
        QDataStream stream(&data, QIODevice::ReadOnly);

		// the same oders and format as in saveSift()
        int matType, rows, cols;
        stream >> matType >> rows >> cols;
        QByteArray siftByte;
        stream >> siftByte;

		// resume the cv::Mat and return
        return cv::Mat(rows, cols, matType, (void*)siftByte.data()).clone();
    }
}