opencv中读写PCA的yaml/yml

从opencv3.4.9中摘取。

static void icvWriteMat( CvFileStorage* fs, const char* name, const void* struct_ptr, CvAttrList /*attr*/ )
{
    const CvMat* mat = (const CvMat*)struct_ptr;
    char dt[16];
    cv::Size size;
    int y;

    assert( CV_IS_MAT_HDR_Z(mat) );

    cvStartWriteStruct( fs, name, CV_NODE_MAP, CV_TYPE_NAME_MAT );
    cvWriteInt( fs, "rows", mat->rows );
    cvWriteInt( fs, "cols", mat->cols );
    cvWriteString( fs, "dt", icvEncodeFormat( CV_MAT_TYPE(mat->type), dt ), 0 );
    cvStartWriteStruct( fs, "data", CV_NODE_SEQ + CV_NODE_FLOW );

    size = cvGetSize(mat);
    if( size.height > 0 && size.width > 0 && mat->data.ptr )
    {
        if( CV_IS_MAT_CONT(mat->type) )
        {
            size.width *= size.height;
            size.height = 1;
        }

        for( y = 0; y < size.height; y++ )
            cvWriteRawData( fs, mat->data.ptr + (size_t)y*mat->step, size.width, dt );
    }
    cvEndWriteStruct( fs );
    cvEndWriteStruct( fs );
}