Multiple Constructors

[Sastraxi]

Ah, now we see where C++ really shines; but can it have multiple class constructors? Say I want to have a LINE class, and declare it (and I don't yet know how classes work.. I'm learning it tonight ):

myline Line = ***; //Is this where the constructor goes?

// Anyway, can I have multiple constructors? Such as:

myline Line = (x1, y1)-(x2, y2) // define a line by two points
myline Line = (x1, y1, m) // define a line by one point and the slope 

[Zaei]

Constructors actually look like this:

Line myLine(x1, y1, x2, y2);
Line myLine2(x, y, m);

And yes, you can have multiple constructors.

Z.

[kedaman]

no big deal, meaningless finesse selling OOP..
You can overloads function names, meaning two functions can have the same name but different arguments, as in argument count, types of those arguments including const modifiers..
constructors are functions and overloaded similarly.

[transcendental]

Sastraxi: You can also write a copy constructor if you intend to create an object with another object as parameter or pass the class object by value.

//class declaration
Class Line
{public:
    //Constructors
    Line();
    Line(int x, int y, int m)
    Line(const Line& line);//copy constructor
    ........
}

How to use,

Line line1(0,0,1);
Line line2(line1);//copy constructor at work
Line *line3=new Line(line1);//copy constructor at work

[Sastraxi]

All very neat little tidbits. The copy constructors will definately come in handy in this case, if say I was to create a parallel line or a perpendicular line. Let's see if I can't make a lil' project...

Thanks guys, you're the best

[Sastraxi]

Okay, I've run into some problems
Dug out my old math texts to do this... oddly enough though I've remembered them all...

// Lines.cpp
#include <iostream>
using namespace std;

class nline {
    double l_m;
    double l_b;
public:
    nline(double x1, double y1, double x2, double y2); // 2x Points
    nline(double x, double y, double m); // Point/Slope
    nline(double m, double b); // y = mx + b
    nline(int a, int b, int c); // Ax + By + C = 0
    ~nline();
    double slope();
    double yint();
};

nline::nline(double x1, double y1, double x2, double y2) {
    l_m = (y2 - y1) / (x2 - x1);
    l_b = y1 - (x1 * l_m);
}

nline::nline(double x, double y, double m); {
    l_m = m;
    l_b = y - (x * l_m);
}

nline::nline(double m, double b) {
    l_m = m;
    l_b = b;
}

nline::nline(int a, int b, int c) {
    l_m = -a / b;
    l_b = c / b;
}

nline::~nline() {
    l_m = 0;
    l_b = 0;
}

double nline::slope() {
    return l_m;
}

double nline::yint() {
    return l_b;
}


int main() {
nline line1(8, -2, 5, 7);
    cout << line1.slope << endl;
    cout << line1.yint << endl;
    return 0;
}
// EOF 

And it spits out like 51 erros. What's wrong? Do classes have to be in header files or something?

[Zaei]

nline::nline(double x, double y, double m); {

Take a good look =P.

Second, if you overload the constructor, you MUST have a default constructor (one that takes no arguments). In your case, it would simply be empty.

Z.

[Sastraxi]

I hate myself Thanks again!

[CornedBee]

You don't NEED the default constructor, but unless you supply one you can't write
nline line;
because that would need the default constructor.

You don't need the destructor: when it is called you can't use the object afterwards anyway, so there is no point in setting the members to 0, it only needs time.

I don't know what exactly you are doing but usually you don't need the precision that double gives you. float needs less memory and often suffices, especially for games.

[Sastraxi]

I'm just doing it for a test, maybe I'll extend it for n-sided figures, linesegs, and points in the future.

[Zaei]

Originally posted by CornedBee
I don't know what exactly you are doing but usually you don't need the precision that double gives you. float needs less memory and often suffices, especially for games.

Its also faster, since a float fits in 32 bits.

Z.