Problem with sorting objects in vector (STL)

[tommyz]

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)

Code:

#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 very much,
tommyz

[kevinkjt2000]

Why does Edge1::weight() return double? Shouldn't it return int?

[tommyz]

Thanks Kevin, Edge1::weight() should return int. I have changed this, but the error still exists.

[kevinkjt2000]

What kind of error are you getting? Is the list just sorted incorrectly? Or is it something crazier?

[tommyz]

The error is default windows error: "There appeared error with Test.exe application and it will be shut down. Sorry for problems"

[Mihay07]

hello..sry for not being able so help you,because i am a beginner and don't now all the things you wrote.(clas,public,functions from algorithm library )and what they do..but for me in situations like this it is a big help to try to debug it..now i see that u use a different ide from what i use..for example i use visual studio,and when i debug,i use f10 to run every line in the code manually step by step..and i watch on the console application(for example) what goes right and what not.and that gives me a small clue where,and what goes wrong..so try to make something like that with you're ide..hope u find the bug :)

[kevinkjt2000]

vector<Edge1*> v;

Try removing the star on that line and see if it works.

[tommyz]

I have debugged this code. The error is in the line 54. sort(v.begin(), v.end(),sortingFunction). In the last call of sortingFunction, one pointer is not valid, when e2->weight() was called this causes error. But the question is, why the pointer is not valid (this pointer is not NULL) ?

[kevinkjt2000]

Maybe try calling sort(v.begin(), v.end()-1, sortingFunction)?

[tommyz]

> Try removing the star on that line and see if it works.

It does not help. I need to have an vector of pointers to Edge1 class, and I want to sort this vector by weight.

[tommyz]

> sort(v.begin(), v.end()-1, sortingFunction)?

This sorts all elements without last one. I want to sort all elements.

[tommyz]

The function sortingFunction is not correct defined.

Correctly:

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

And algorithm works good.

Thanks all!