Keep a stream from fstream open through member functions

Question

Hi, I am trying to keep a stream to a file /dev/fb0 (linux framebuffer) open throughout several Qt member functions. The goal is to use a myscreen::connect function to open up the framebuffer

bool myscreen::connect()
{
std::fstream myscreen_Fb;
myscreen_Fb.open("/dev/fb0")
QImage* image;
image = new QImage(w, h, QImage::Format_RGB888);
QScreen::data = image->bits();
}

This would ideally open the frame buffer and create a new QImage to act as a memory buffer for the data being written to the screen. Then my "image" would point to the first visible pixel (memory) on the screen through the bits() function. I have to implement this because my hardware does not support the default memory mapping.

I would then like to blit it to the screen with:

void myscreen::blit(const QImage &img, const QPoint &topLeft, const QRegion &region)
{

QScreen::blit(img, topLeft, region);
write(myscreen_Fb, image.bits(), image.size());
}

I cant seem to get the pointer to the first visible pixel open to use and get complaints from GCC about myscreen_Fb not being declared in the scope. Any ideas?

update

I made the changes suggested and declared the function in the class but get this error which is driving me crazy.

error: expected constructor, destructor, or type conversion before '.' token

It refers to the line which contains:

vopuscreenFd.open("/dev/fb0", fstream::out);

Bryce

Answer 1

You declared myscreen_Fb in the scope of only the "connect" function. Either make it a member of the myscreen class, or even better just pass it as an argument to the "blit" function.

Answer 2

That is because myscreen_Fb is, in fact, not declared in the scope of the blit function. Here you declared it in the connect() function.

Declare myscreen_Fb as a member variable of the myscreen class. It will be accessible to all functions in that instance of the class.

class myscreen
{
  public:
     myscreen( void );
    ~myscreen( void );

    bool
    connect  ( void );

    void 
    blit     ( const QImage &img, 
               const QPoint &topLeft, 
               const QRegion &region)

  private: 
    std::fstream myscreen_Fb;
};

In relation to this question: "I cant seem to get the pointer to the first visible pixel open to use", what exactly do you mean here? All I can presume is that you mean to use blit using the image ptr you created within connect, which is also not yet a member variable, so perhaps you want to do this:

bool myscreen::connect()
{
    std::fstream myscreen_Fb;
    myscreen_Fb.open("/dev/fb0")
    QImage* image;
    image = new QImage(w, h, QImage::Format_RGB888);
    //QScreen::data = image->bits();   //don't need this?
    blit( image, "topleft ref", "region ref");     //add this, replacing 
                                                   // "topleft ref" and
                                                   // "region ref" with correct 
                                                   // values you've pulled
}

and the write function within myscreen::blit get's the ptr to the first pixel. I am making a lot of presumptions here because the question is a bit unclear.