CODEWITHSUNDEEP
c++classobject
Shadow
Shadow

Reputation: 447

How to make multiple instances of a class in C++

How do you create multiple class instances without individually typing in their names?

int main(){
    myClass myInstance_1;
    myClass myInstance_2;
    myClass myInstance_3;
    ...
    myClass myInstace_10;
}

Upvotes: 5

Views: 25728

Answers (5)

dif
dif

Reputation: 35

Just like Jarod42's code:

int main(){
    std::vector<myClass> myInstances;
    for(int i = 0; i < 10; ++i) {
        myInstances.push_back(myClass(i));
    }
    myInstances[5].myClassFunction();
}

I think these should work.

Upvotes: 0

Adrian Maire
Adrian Maire

Reputation: 14835

Solution 1: Use an array of integers as an initializer, the constructor is used to convert the integer to myClass.

class myClass
{
public:
    //constructor
    myClass( int num) {m_number = num;};

    void myClassFunction(){cout<< "I am " << m_number << endl;}
private:

    int m_number;
};

int main(){
    myClass myInstance[10] = {0,1,2,3,4,5,6,7,8,9};
    for ( int i=0; i< 10; i++) myInstance[i].myClassFunction();
}

Solution 2: Use a static counter to set m_number, so no need to use a non-default constructor. 

class myClass
{
public:
    //constructor
    myClass(){m_number=counter++;};

    void myClassFunction(){cout<< "I am " << m_number << endl;}
private:

    int m_number;
    static int counter;
};
int myClass::counter = 0;

int main(){
    myClass myInstance[10];
    for ( int i=0; i< 10; i++) myInstance[i].myClassFunction();
}

Solution 3: Set the m_number after the constructor call, so the default constructor is enough.

class myClass
{
public:
    //constructor
    void setNum(int num){m_number=num;};

    void myClassFunction(){cout<< "I am " << m_number << endl;}
private:

    int m_number;
};

int main(){
    myClass myInstance[10];
    for ( int i=0; i< 10; i++) myInstance[i].setNum(i);
    for ( int i=0; i< 10; i++) myInstance[i].myClassFunction();
}

Upvotes: 3

toutnom
toutnom

Reputation: 244

Use array:

myClass myInstance[10];

This will create an array with 10 instances but each instance will have its m_number set to 0.

Another approach:

myClass *myInstance = new myClass[10];

for (unsigned int i = 0; i < 10; i++)
{
myInstance[i] = new myClass(i);
}

Here each instance will have different m_number values

Edit for the sake of fixing the problem with above code. Better solutions have already been proposed.

myClass *myInstance[10];

// Allocate
for (unsigned int i = 0; i < 10; i++)
{
myInstance[i] = new myClass(i);
}

// At the end free
for (unsigned int i = 0; i < 10; i++)
{
delete myInstance[i];
}

Upvotes: -2

Galik
Galik

Reputation: 48615

How do you create multiple class instances without individually typing in their names?

The answer is you make an array, but not the way you tried it.

Like this:

int main()
{
    MyClass myInstance[10];

    for(int i = 0; i < 10; i++)
    {
        myInstance[i].myClassFunction();
    }
}

TIP: Don't use arrays, use std::vector or std::array.

(see answer from @Jarod42)

Upvotes: 3

Jarod42
Jarod42

Reputation: 217275

You may do the following:

int main(){
    std::vector<myClass> myInstances;
    for(int i = 0; i < 10; ++i) {
        myInstances.emplace_back(i);
    }
    myInstances[5].myClassFunction();
}

Upvotes: 7

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