Thread: Memory leak With new

For some reason my function isn't changing the pointer I send to it.

Code:

void insertOrder (dnode<T> *header, const T& item){
header=new dnode<T>(item);
}
//main
dnode<int> *tree=NULL;

insertOrder(tree,rando);//Random number from 0-99

Whenever I run the program header keeps being NULL.

The whole point of & in a function prototype is "this function will change this variable". By contrast, if you don't have &....

The reason why you must use the reference symbol above might become clear when you learn what a pointer actually is.

A pointer is just a number. You could turn your pointer into an unsigned int type and use this instead. A pointer type in c/c++ is just to let you and the compiler know that the number contained is to be treated as a memory address. So, if you dont pass by reference, then all you are doing is changing the numeric value of header within the function call and nothing else.

Code:

void insertOrder (unsigned int header, const T& item){
header=new dnode<T>(item);
}

So, I hope this explains why you must use this code instead. Pass by reference so the number returned by the new function actually is stored in the pointer you pass to the function.

Code:

void insertOrder (dnode<T>* &header, const T& item){
header=new dnode<T>(item);
}

Originally Posted by smasherprog

A pointer is just a number. You could turn your pointer into an unsigned int type and use this instead

can you give example , i cant get this to compile

Code:

class A
{
};

int main()
{
	unsigned int p = new A;
}

Code:

invalid conversion from ‘A*’ to ‘unsigned int’

You can "turn your pointer into an unsigned int type".

Code:

double a = 4.0;
double* b = &a; //can be pointer to whatever but just for example
unsigned int c = (unsigned int) b; //turn your pointer into an unsigned int

Not that is actually a good idea. But you can.

Ah yes & fixed it. I was forced to use the function prototype

void insertOrder (dnode<T> *header, const T& item)

I figured I wasn't passing the values correctly and it was only copying the address. thanks guys.