Passing structs in functions

Chada · 03-04-2007 1:27pm #1

Hey,

quick question:

When you are passing a struct to a function how exactly is the best way (in c++) to call that function ?

For example:

unit::renderSelection(SDL_Surface *screen, unitlocs location) // << unitlocs is a //struct + location is an object of it

But when i go to call the function later in main like so:
(inside a draw() method)
theUnit->renderSelection(screen, location);

I get errors that location is undeclared.

I have included the class that the function comes from in my main, and my pointer is as follows:

unit *theUnit = new unit();

So can anyone enlighten me as to how to properly call this function ? I tried using a pointer to the struct but that didnt work either

joe_chicken · 03-04-2007 1:59pm

Have you tried declaring an instance of unitlocs and passing that in?

Not sure of the interface you're using, but I presume an instance of SDL_Surface* called "screen" is declared somewhere...

structs get passed in the same way as everything else

Chada · 03-04-2007 2:10pm

Sorry i wasn't clear before, SDL_Surface *screen is a pointer to the surface where the renderSelection is going to be drawn to, its fine.

Its this struct unitlocs, i've created instances of it like so:

struct unitlocs {
Point2D location;
Point2D destination;
}

With point2d being another struct in a different class with generic getX() and getY() methods.

When i call the unitlocs location into a function, im able to make struct method calls like location.getX() etc. without a problem.

But when i try and call the actual function renderSelection() from main, it doesn't recognise location as an instance of unitlocs.

As iv shown before iv tried many variances but still get errors:


theUnit->renderSelection(screen, location);

theUnit->renderSelection(screen, unitlocs location);

How do you call a method with an external struct in it without get these undeclared errors ?

joe_chicken · 03-04-2007 2:49pm

try use typedef struct

typedef struct { 

Point2D location;
Point2D destination;

} unitlocs;

unitlocs unitlocs_struct;
theUnit->renderSelection(screen, unitlocs_struct);

Chada · 03-04-2007 4:25pm

Tried your way mate, got the same error:

128 C:\DanZelda\DanZelda\main.cpp `unitlocs_struct' undeclared (first use this function)

Iv'e included all the files needed im just kinda stuck as to why it won't let me call the function.

this is the draw() function in main im trying to get it to run in:

void draw(engine *theEngine, SDL_Surface *back, SDL_Surface *screen, Selection *theSelection,
 unit *theUnit, player *thePlayer, vector<orc *> badGuys, vector<sprite *> goodGuys, vector<unit *> units, vector<baseBuilding *> buildings, vector<sprite *> screenInfo)
{
    theEngine->Display->drawSurface(back, backX, backY, screenWidth, screenHeight, screen);  
    drawSprite(thePlayer, theEngine, screen); 

    vector<sprite *>& playerArrows = thePlayer->getWeapon();
    for(unsigned int i=0; i < playerArrows.size(); i++)
    {
        if(playerArrows[i] != NULL)
        {
            drawSprite(playerArrows[i], theEngine, screen);
        }
    }


    for(unsigned int i=0; i < goodGuys.size(); i++)
    {
        drawSprite(goodGuys[i], theEngine, screen);
    }
    
    for(unsigned int i=0; i < badGuys.size(); i++)
    {
        drawSprite(badGuys[i], theEngine, screen);
    }
    for(unsigned int i=0; i < units.size(); i++)
    {
        drawSprite(units[i], theEngine, screen);
    }
    for(unsigned int i=0; i < buildings.size(); i++)
    {
        drawSprite(buildings[i], theEngine, screen);
    }

    
    for(unsigned int i=0; i< screenInfo.size(); i++)
    {
        drawSprite(screenInfo[i], theEngine, screen);
    }

    vector<sprite *>& playersLife = thePlayer->getLifeIcon();
    for(unsigned int i=0; i < thePlayer->getLife(); i++)
    {
        if(playersLife[i] != NULL)
        {
            drawSprite(playersLife[i], theEngine, screen);
        }
    }

    string msg = font->IntToString(thePlayer->getScore());
    int fw = (font->getTextWidth(msg))/2;
    font->write(screen,msg,140-fw,20);
    
    
    //drawMySprite(goodGuys[0], theEngine, screen);
    theSelection->update();
    theSelection->render(screen);
    [B]theUnit->unitSelection(selection, unitlocs_struct);
    theUnit->renderSelection(screen, unitlocs_struct);    [/B]                 
    SDL_Flip(screen);
    

}

Anything look wrong there ? All the pointers called by draw are delcared inside main.

joe_chicken · 03-04-2007 4:45pm

where are you creating the instance of unitloc?

you should do that from inside the function, and make sure to initialise...

i.e.

typedef struct {
       ......
} mystruct;


function()
{
     mystruct a_struct;
     
...........
...initialise......
...........


     use_struct(a_struct);
}

Chada · 03-04-2007 5:18pm

Ah right im with ya now, so just so i duplicate this technique over to my functions and to make sure i'm right:

typedef struct unitlocs{
Point2D location;
Point2D destination;

int getXunitloc(blah)
{
......
}
int getYunitloc(blah)
{
.....
}
} unitLoc;

class unit: public sprite
{
renderSelection(SDL_Surface *screen, unitLoc unitlocs_struct)
}
// now inside me .cpp file:

....

void unit::renderSelection(SDL_Surface *screen, unitLoc unitlocs_struct)
{
    unitLoc unitlocs_struct = getUnitlocation();    

     if(unitState == SELECTED)
     {
       circleColor( screen, unitlocs_struct.getXUnitLocation(), unitlocs_struct.getYUnitLocation(), 10 , 0xfe00008b);         
     }            
     
}   

}

Is that correct ?

And then call theUnit->renderSekection(screen, unitlocs_struct) in main.cpp ?

joe_chicken · 04-04-2007 8:51am

if you want to put functions in your struct, you should use a class

Chada · 04-04-2007 1:21pm

Thanks for help joe, got it working by delcaring an instance of each struct in my header file and then it was able to look them up from there.

Although my renderSelection still isn't drawing the circle around the unit but thats another story

Chada · 04-04-2007 1:22pm

Thanks for help joe, got it working by delcaring an instance of each struct in my header file and then it was able to look them up from there.

Although my renderSelection still isn't drawing the circle around the unit but thats another story

Passing structs in functions

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