C++ Object referencing in different scopes - c++

Question

I have a class Rect such that it holds the width, height, x and y values of a shape. The class can draw using the values in the parameter and move the drawn rect.
Rect::Rect(w, h, x, y, const std::string &image_path) : _w(w), _h(h),
_x(x), _y(y)
{
SDL_Surface *surface = IMG_Load(image_path.c_str());
if (!surface) {
std::cerr << "Failed to create surface.";
}
//create texture
texture = SDL_CreateTextureFromSurface(Window::renderer, surface);
if (!texture) {
std::cerr << "Failed to create worker texture.";
}
SDL_FreeSurface(surface);
}
Rect::~Rect()
{
SDL_DestroyTexture(texture);
}
Rect::draw()
{
//where the constructor parameters are parsed
SDL_Rect rect= {_x, _y, _w, _h} ;
//extra code about some SDL texture stuff and RenderCopy
}
Rect::moveX(int x){
_x +=x;
}
In my Unit class, I include the class Rect and I create my units, draw them in the same function. There is another function in unit that moves rect by checking another value from another class that changes.
Unit::Unit()
Unit::~Unit()
void Unit::createUnit(int type, int x, int y){
if (type == 0)
{
Rect unit1(unitImageWidth, unitImageSizeHeight, x, y, "res/unit1.png");
}
if (type == 1)
{
Rect unit2(unitImageWidth, unitImageSizeHeight, x, y, "res/unit2.png");
}
}
void Unit::moveUnit(int x){
if(selection == 0)
{
unit1.movex(x);
}
if (selection == 1)
{
unit2.movex(x);
}
}
My question is:
When in Unit::moveUnit(), how can I reference the object Rect "unit1" and Rect "unit2" that are initialized in Unit::createUnit()?
When I try to compile, it say that unit1 and unit2 are undefined.

Answer 1

You can't do what you want to do. Non-static local variables are bound to their scope. They are only visible inside and are destroyed when the program exits the area bounded by the {} braces.
The simplest solution is to go in a completely different direction. Add to Unit a private variable to contain the Rect for example,
Rect sprite;
Then replace
void createUnit(int type, int x, int y);
with a Unit constructor
Unit(int type, int x, int y);
And implement the constructor something like
Unit::Unit(int type, int x, int y): sprite(unitImageWidth,
unitImageSizeHeight,
x,
y,
type == 0? "res/unit1.png": "res/unit2.png")
{
}
The colon : starts a Member Initializer List and that crazy ?: Is a one line if statement called the Ternary or Conditional Operator
Note: I don't know what unitImageWidth and unitImageSizeHeight are or where they come from. Make sure you do and make sure they are accessible.
moveUnit becomes
void Unit::moveUnit(int x)
{
sprite.movex(x);
}
because sprite knows what it is and what image has been loaded and can move the Rect to x (or whatever movex does).
To use you
Unit myUnit(0, 1024, 42); // creates a unit of type 0 at coordinates 1024,42
myUnit.movex(88); // moves myUnit to 88,42 (I think)

Answer 2

Just add two Rect members in your class Unit, then you can use it in different member functions.
Better using pointer, as below:
class Unit
{
public:
Unit::Unit()
: uint1(NULL), uint2(NULL){};
Unit::~Unit()
{
if (uint1 != NULL) {
delete unit1;
uint1 = NULL;
}
if (uint2 != NULL) {
delete unit2;
uint2 = NULL;
}
};
void Unit::createUnit(int type, int x, int y)
{
if (type == 0) {
unit1 = new Rect(unitImageWidth, unitImageSizeHeight, x, y, "res/unit1.png");
}
if (type == 1) {
unit2 = new Rect(unitImageWidth, unitImageSizeHeight, x, y, "res/unit2.png");
}
}
void Unit::moveUnit(int x)
{
if (selection == 0) {
unit1->movex(x);
}
if (selection == 1) {
unit2->movex(x);
}
}
private:
Rect *unit1;
Rect *unit2;
};