Help With Vectors

[jgeorge]

Hello everyone,
As a high school student I've been working game in my spare time as a way of furthering my programming skills, however I recently ran into a roadblock when attempting to learn vectors and convert some of my arrays into vectors.

I've been running into segmentation faults no matter how much I work on it and I think its due to how I'm defining objects in the vector.

Here's some snippets of the related code:

//Asteroid.h

vector <float> GlobalAsteroidX;
vector <float> GlobalAsteroidY;

vector <int> AsteroidCurrentHealth;
vector <int> AsteroidHeading;

//Asteroid.cpp

void Asteroid::Rand(int AsteroidCount) //randomly generates the X,Y and Heading of asteroids
{
    for (int c = 0; c < AsteroidCount; c++)
    {
        GlobalAsteroidX[c] = rand()%GameWidth+1;
        GlobalAsteroidY[c] = rand()%GameHeight+1;

        AsteroidHeading[c] = rand()%360+1;

        AsteroidCurrentHealth[c] = 100;
    }
}

//Main.cpp
//If Mouse clicks button -> then
    global.AsteroidCount = 350;
    as.Rand(global.AsteroidCount);

Its seems the program crashes after the Rand function runs. Can anyone give me advice on if I'm doing something wrong here? Thanks in advance.

[zb0S216C]

With the code that you posted, you seem to be violating the bounds of the vector (s). The vector (s) need to be pushed-back for it/them to grow. For example:

std::vector<int> ints; // No items within this vector.

ints.push_back(10);    // There's 1 item within the vector, now. 

Try altering the for to something like this:

for(unsigned int cycle(0U); cycle < AsteroidCount; ++cycle)
{
    GlobalAsteroidX.push_back((rand() % GameWidth) + 1);
    GlobalAsteroidY.push_back((rand() % GameHeight) + 1);

    AsteroidHeading.push_back((rand() % 360) + 1);
    AsteroidCurrentHealth.push_back(100);
}

At the end of the loop, AsteroidCount items will be pushed into the corresponding vector. I would suggest structures, though, for an asteroid object.

_Wazzak

[jgeorge]

Thank you, that makes a lot more sense!
Unfortunately I'm still running into some errors. Regarding using the information within the vector, how exactly can I check and/or modify those values? For example, I have the code pasted below and I'm not sure if the syntax stays the same or do I need to change it for checking within vectors?

void Asteroid::InRange(float GlobalPlayerX, float GlobalPlayerY, float PlayerArmor, int& PlayerCurrentHealth, int AsteroidCount, bool Debug)
{
    for (int c = 0; c < AsteroidCount; c++)
    {
        if ((GlobalAsteroidY[c] - GlobalPlayerY >= AsteroidRange * -1 && GlobalAsteroidY[c] <= GlobalPlayerY) || (GlobalAsteroidY[c] - GlobalPlayerY <= AsteroidRange && GlobalAsteroidY[c] >= GlobalPlayerY)) //Checks if Player's Y values is close enough
        {
            if ((GlobalAsteroidX[c] - GlobalPlayerX >= AsteroidRange * -1 && GlobalAsteroidX[c] <= GlobalPlayerX) || (GlobalAsteroidX[c] - GlobalPlayerX <= AsteroidRange && GlobalAsteroidX[c] >= GlobalPlayerX)) //Checks if Player's X value is close enough
            {
            PlayerCurrentHealth -= AsteroidAttack / PlayerArmor; //Player takes damage

            if(Debug == true)
            {
            std::cout << "Asteroid #" << c <<" (Hit) || Player Health: " << PlayerCurrentHealth << endl; //Print out
            }
            }
        }
        else
        {
            //Place holder
        }
    }
}

[zb0S216C]

dev geo wrote:

"how exactly can I check and/or modify those values?" (sic)

There's two ways you can access the data within a vector:

1) Use the vector::at() method. This returns a non-constant reference to the specified item.
2) Use the overloaded vector::operator[] operator.

Both do the same thing. However, vector::at() throws an std::out_of_range exception when the bounds of the vector are exceeded. The overloaded operator, however, doesn't, which effectively allows you to write to an unknown section of memory without generating a run-time error. The choice is yours.

Here's an example that uses both of the latter:

// Create a new vector with two items, both of which have the value of zero.
std::vector<int> new_vector(2, 0);

std::cout << "Values are: ";

// Using the overloaded sub-script operator:
std::cout << new_vector[0U] << ", ";

// Using vector::at():
std::cout << new_vector.at(1U)

std::endl(std::cout);

dev geo wrote:

"I'm not sure if the syntax stays the same or do I need to change it for checking within vectors?" (sic)

The syntax is the same.

_Wazzak

[jgeorge]

Thanks again!
You've helped me tons.