SDL_surface that contains several images - c++

Question

Suppose I have a SDL_Surface that is just one image.
What if I wanted to make that SDL_Surface have three copies of that image, one below the other?
I came up with this function, but it doesn't show anything:
void ElementView::adjust()
{
int imageHeight = this->img->h;
int desiredHeight = 3*imageHeight;
int repetitions = desiredHeight / imageHeight ;
int remainder = desiredHeight % imageHeight ;
SDL_Surface* newSurf = SDL_CreateRGBSurface(img->flags, img->w, desiredHeight, 32, img->format->Rmask, img->format->Gmask, img->format->Bmask,img->format->Amask);
SDL_Rect rect;
memset(&rect, 0, sizeof(SDL_Rect));
rect.w = this->img->w;
rect.h = this->img->h;
for (int i = 0 ; i < repetitions ; i++)
{
rect.y = i*imageHeight;
SDL_BlitSurface(img,NULL,newSurf,&rect);
}
rect.y += remainder;
SDL_BlitSurface(this->img,NULL,newSurf,&rect);
if (newSurf != NULL) {
SDL_FreeSurface(this->img);
this->img = newSurf;
}
}

Answer 1

I think you should
Create a new surface that is 3 times as long as the initial one
Copy from img to the new surface using code similar to what you have (SDL_BlitSurface), except having the destination as your new surface
SDL_FreeSurface on your original img
Assign your new surface to img
Edit: Here is some sample code, didn't have time to test it though...
void adjust(SDL_Surface** img)
{
SDL_PixelFormat *fmt = (*img)->format;
SDL_Surface* newSurf = SDL_CreateRGBSurface((*img)->flags, (*img)->w, (*img)->h * 3, fmt->BytesPerPixel * 8, fmt->Rmask, fmt->Gmask, fmt->Bmask, fmt->Amask);
SDL_Rect rect;
memset(&rect, 0, sizeof(SDL_Rect));
rect.w = (*img)->w;
rect.h = (*img)->h;
int i = 0;
for (i ; i < 3; i++)
{
SDL_BlitSurface(*img,NULL,newSurf,&rect);
rect.y += (*img)->h;
}
SDL_FreeSurface(*img);
*img = newSurf;
}