Back to For Beginners

is there a less stupid way to initialize a vector?

For Beginners

Started by draconar February 20, 2010 09:32 AM

10 comments, last by SiCrane 14 years, 1 month ago

draconar

130

Author

February 20, 2010 09:32 AM

Here, I know that for a vector of a "primitive" type, we can initialize it using:


vector<int> myInts(100);

the vector will be initialized with a 100 spaces filled with zeros. Now, I'm playing with a particle system using OpenGL and I want to do something like this:



std::vector<Particle> particles(1000);

but it won't compile. the type Particle is a class using the default constructors and destructors, and filled with hand-made, declared "default" variables. This class could be a struct by any means... As it won't compile, I'm initializing the vector using



    for(int i = 0; i < MAX_PARTICLES; i++){
        Particle *particle = new Particle();
        particles.push_back(*particle);
    }

any help is welcomed! cheers, Fabio

rip-off

11,000

February 20, 2010 09:35 AM

Compilers generally give error messages when they refuse to compile code. What error message are you getting?

The following code leaks memory like a sieve... full of memory.

for(int i = 0; i < MAX_PARTICLES; i++){    Particle *particle = new Particle();    particles.push_back(*particle);}

You know you can do this:

for(int i = 0; i < MAX_PARTICLES; i++){    // Pass a temporary particle to push_back()    particles.push_back(Particle());}

blog | twitter

DevFred

840

February 20, 2010 09:46 AM

Quote:Original post by draconar
std::vector<Particle> particles(1000);
but it won't compile.

Then Particle does not have a visible default constructor or is an incomplete type at this point.

draconar

130

Author

February 20, 2010 10:11 AM

here is the error message when I use

std::vector<Particle> particles(1000);

main.cpp:130: error: expected identifier before numeric constant
main.cpp:130: error: expected ‘,’ or ‘...’ before numeric constant

DevFred, the class Particle hasn't a default constructor. Now I have provided one and the error continues..

SiCrane

11,840

February 20, 2010 10:15 AM

Post a complete, but minimal, code sample that demonstrates your problem.

draconar

130

Author

February 20, 2010 10:24 AM

Quote:Original post by SiCrane
Post a complete, but minimal, code sample that demonstrates your problem.

here it goes:

//The squareclass Square{    private:    //The offsets    int x, y;    //The velocity of the square    int xVel, yVel;    public:    //Initializes    Square();    //Handles key presses    void handle_input();    //Moves the square    void move();    //Shows the square on the screen    void show();    std::vector<Particle> particles(1000);    std::vector<Particle>::iterator particle_iter;    };

I want the vector Particle to be a member of Square (as in composition).

The Particle class (defined above Square)

class Particle{public:        Particle(){    active = true; /* Active (Yes/No) */    life = 1.0;   /* Particle Life   */    fade = ( float )( rand( ) %100 ) / 1000.0f + 0.003f;   /* Fade Speed      */    r = colors[0][0];      /* Red Value       */    g = colors[11][1];      /* Green Value     */    b = colors[5][0];      /* Blue Value      */    x = 0.0;      /* X Position      */    y = 0.0;      /* Y Position      */    z = 0.0;      /* Z Position      */    xi = 0.0;     /* X Direction     */    yi = 0.0;     /* Y Direction     */    zi = 0.0;     /* Z Direction     */    xg = 0.0;     /* X Gravity       */    yg = -.8;     /* Y Gravity       */    zg = 0.0;     /* Z Gravity       */    }   PARTICLE MEMBERS (vars) ARE HERE (NOT SHOWN)    };

Wan

1,366

February 20, 2010 10:25 AM

Seems like you're initializing something in a declaration.

mattd

1,078

February 20, 2010 10:27 AM

That isn't how you use a non-default constructor to construct a member of a class.

You do it in the class's initializer list.

Change
std::vector<Particle> particles(1000);
to just:
std::vector<Particle> particles;

Have this as the class's constructor:

Square::Square() : particles(1000) {    // ...}

draconar

130

Author

February 20, 2010 10:37 AM

Quote:Original post by mattd
That isn't how you use a non-default constructor to construct a member of a class.

You do it in the class's initializer list.

Change
std::vector<Particle> particles(1000);
to just:
std::vector<Particle> particles;

Have this as the class's constructor:
Square::Square() : particles(1000) {    // ...}

OUCH. that hurts. have completely forgotten about this.

Worked like a charm. Thank you very much you all, guys!

iMalc

2,466

February 20, 2010 12:45 PM

I think you may have gotten confused with C#, which does allow the kind of initialisation in the manner you were doing, IIRC.

"In order to understand recursion, you must first understand recursion."
My website dedicated to sorting algorithms

is there a less stupid way to initialize a vector?

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

is there a less stupid way to initialize a vector?

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

Reticulating splines