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TimChan

[SOLVED]A problem related to vectorpointer

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The output is something like below: original address: 0x3d3770 2 new address(?): 0x289d720 Plus an error message from the system. And the source:
#include <iostream>
#include <vector>

using namespace std;

class CNum {
	public:
	CNum(int _value) : Value(_value) {}
	
	int Value;
};

vector<CNum*> Nums;

void find_num(int _n, CNum* _pointer) {
	vector<CNum*>::iterator i;
	for(i = Nums.begin(); i != Nums.end(); ++i) {
		if((*i)->Value == _n) _pointer = *i;
	}
	cout << "original address: " << _pointer << endl;
	cout << _pointer->Value << endl;
}

int main() {
	Nums.push_back(new CNum(1));
	Nums.push_back(new CNum(2));
	Nums.push_back(new CNum(3));
	
	CNum* target;
	find_num(2, target);
	cout << "new address(?): " << target << endl;
	cout << target->Value << endl;
	
	return 0;
}



How come the address changes after the return of the function find_num?

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In your code, the value of target never changes.

In particular, the value of target is not changed by the find_num(2, target); code. This is because a copy of target is passed to find_num (which takes its second argument by value), and the passed copy is modified without altering the original.

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Thank you.

The problem is solved by simply change "find_num(int _n, CNum* _pointer)" to "find_num(int _n, CNum*& _pointer)".

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Your program has memory leaks. The memory that you dynamically allocate for the CNums which the vector is holding pointers to is never released. A vector will not automagically delete this memory.

You are going to have to loop through the vector manually deleting it's the pointers.

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