Problem with sorting objects in vector (STL)

[tommyz4]

Hi,

I spent a lot of hours, why this code is wrong.
This code compiles good, but execution causes errors (during sorting objects).
Environment: (MinGW WinXP or VS 2008)

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

class Edge1 {
	int v_,w_,weight_;
public:
	Edge1(int v, int w, double weight) {
		v_ = v;
		w_ = w;
		weight_ = weight;
	};
	~Edge1();
	int v() const {
		return v_;
	};
	int w() const {
		return w_;
	};
	int weight() const{
		return weight_;
	};
};

bool sortingFunction(const Edge1 *e1, const Edge1 *e2) {
	return e1->weight() <= e2->weight();
}

int main() {

	vector<Edge1*> v;

	v.push_back( new Edge1(0,6,3) );
	v.push_back( new Edge1(0,1,82) );
	v.push_back( new Edge1(1,9,73) );
	v.push_back( new Edge1(1,8,91) );
	v.push_back( new Edge1(2,3,15) );
	v.push_back( new Edge1(2,7,99) );
	v.push_back( new Edge1(3,5,90) );
	v.push_back( new Edge1(3,0,18) );
	v.push_back( new Edge1(4,0,63) );
	v.push_back( new Edge1(4,3,36) );
	v.push_back( new Edge1(5,1,44) );
	v.push_back( new Edge1(5,4,82) );
	v.push_back( new Edge1(6,4,15) );
	v.push_back( new Edge1(6,7,17) );
	v.push_back( new Edge1(8,3,73) );
	v.push_back( new Edge1(8,2,13) );
	v.push_back( new Edge1(9,4,66) );
	v.push_back( new Edge1(9,0,3) );

	cout << "Start sorting..." << endl;
	sort(v.begin(), v.end(),sortingFunction);
	cout << "Stop sorting" << endl;  // in this case never happened

	return 0;
}

Thank you veru much
tommy

[StuXYZ]

Your problem is the equals sign (=) in your sort function.
You cannot e.g. this allows

Edge1 A(0,0,1);
Edge1 B(0,0,1); 

// This should not be true to use the algorithm sort.
sortFunction(&A,&B) == sortFunction(&B,&A)

Also please use a managed point with vectors, e.g. boost::shared_ptr.

[tommyz4]

Thank you StuXYZ! You are right.
I have changed the method:

bool sortingFunction(const Edge1 *e1, const Edge1 *e2) {
	return e1->weight() < e2->weight();
}

Thanks! :)

[Ancient Dragon]

weight_ is an integer, but the parameter in the constructor has it as a double. Which is it???

The sortingFunction() function should use < operator, not <=.

[edit]Oops! already answered.

[tommyz4]

> weight_ is an integer, but the parameter in the constructor has it as a double. Which is it???

This is my mistake, should be int. Thanks Ancient Dragon.

[mrnutty]

Also whats with pointers? Be smarter about your code and use reference or smart pointers if you have to.

[Ancient Dragon]

I agree -- but I'm just as guilty about not using smart pointers. Here's a link that shows how to use them.