asked on C++ dynamic creation of objects
Hello all,
I have a couple of questions reagarding the new keyword in C++. First, can someone tell exactly what is the difference between the following two code segments:
Secondly, Ive read that the following segment of code will lead to a memory leak after the b = a assignment is made. My question is, will the second segment of code also lead to a memory leak?
Thanks
I have a couple of questions reagarding the new keyword in C++. First, can someone tell exactly what is the difference between the following two code segments:
Account a = Account(35.00, 34234324);
Account *ptrA = &a;
Account *a = new Account("John", 10.50, 123456);
Secondly, Ive read that the following segment of code will lead to a memory leak after the b = a assignment is made. My question is, will the second segment of code also lead to a memory leak?
Thanks
int main()
{
Account *a = new Account("John", 10.50, 123456);
Account *b = new Account("Derek", 12.07, 123457);
a->display();
b->display();
b = a;
a->display();
b->display();
}
int main()
{
Account a = Account(35.00, 34234324);
Account *ptrA = &a; 1
CurrentAccount b = CurrentAccount(50.0, 12345, 200.0);
CurrentAccount *ptrB = &b; 2
cout << "Displaying ptrA:" << endl;
ptrA->display(); 3
cout << "Displaying ptrB:" << endl;
ptrB->display(); 4
ptrA = ptrB; 6
cout << "Displaying ptrA again:" << endl;
ptrA->display(); 7
}
C++
Last Comment
ambience
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BTW, you might want to check out smart pointers (http://en.wikipedia.org/wiki/Smart_pointer) to avoid such leaks. The Wikipedia article has both examples and further links.
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first: static variable
Account a = Account(35.00, 34234324);
Account *ptrA = &a;
a have alloc memory in stack and it will automatically free when the function finish.
ptrA = &a : it only create a pointer not a new object.
second: dynamic variable
Account *a = new Account("John", 10.50, 123456);
create a object in heap memory an return a pointer.
you can access object through pointer.
and when you not need object you have to free it by statement:
delete a;
Account a = Account(35.00, 34234324);
Account *ptrA = &a;
a have alloc memory in stack and it will automatically free when the function finish.
ptrA = &a : it only create a pointer not a new object.
second: dynamic variable
Account *a = new Account("John", 10.50, 123456);
create a object in heap memory an return a pointer.
you can access object through pointer.
and when you not need object you have to free it by statement:
delete a;
Do you also happen to know the operator precedence rules for '*facepalm*'? Sorry, but that had already been mentioned.
There is NO memory leak in your 3rd snippet. It is perfectly OK
Account a = Account(35.00, 34234324);
Account *ptrA = &a;
// ptrA only takes the address of a. a exists on the stack.
// Another way to say that is that ptrA does not "own" a it just points to it.
CurrentAccount b = CurrentAccount(50.0, 12345, 200.0);
CurrentAccount *ptrB = &b; 2
// ptrB only takes the address of b. b exists on the stack.
ptrA = ptrB; 6
// ptrA now points to b
cout << "Displaying ptrA again:" << endl;
ptrA->display(); 7
// no need to delete, actually it would probably crash if you did so because
// the objects exist on stack.
Account a = Account(35.00, 34234324);
Account *ptrA = &a;
// ptrA only takes the address of a. a exists on the stack.
// Another way to say that is that ptrA does not "own" a it just points to it.
CurrentAccount b = CurrentAccount(50.0, 12345, 200.0);
CurrentAccount *ptrB = &b; 2
// ptrB only takes the address of b. b exists on the stack.
ptrA = ptrB; 6
// ptrA now points to b
cout << "Displaying ptrA again:" << endl;
ptrA->display(); 7
// no need to delete, actually it would probably crash if you did so because
// the objects exist on stack.
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