Thread: Problems with sorting

You can't initialize a variable like this:

Code:

		int Action2 = 0;

You can only define it at that stage. If there were a class definition, you could make a class constructor to fix it. I'm not sure how to fix this without digging into the book.

Todd

Yes I just figured out as I got your answer so I deleted the code just before.
So I have compile success when declaring it like: int Action2
But I only have this If I do this with the line that do the sort for Values:

//std::sort(Values.begin(), Values.end());

So something must be wrong here. The thing is that I will sort for the Action value. Perheps this should be specified in any way.

Code:

#include "stdafx.h"
#include <iostream>
#include <fstream>
#include <sstream> 
#include <string>  
#include <vector>
#include <cmath>
#include <algorithm>

struct Value 
	{
		int Action2;
		std::string Symbol2;
	};

using namespace std;
int main () 
{ 
	
	char Comma;
	int t = 0;
	std::string Symbol;
	int Action = 0;
	std::vector<Value> Values (3);


	ofstream Sort1;
  
	Sort1.open ("Sort1.txt");
	ifstream Sort ("Sort.txt");

	while	(    getline(Sort, Symbol, ',')   )           		
	{
		t = (t + 1);		// Count
		
		Sort >> Action;		// Buy

			Values[t].Symbol2 = Symbol;
			Values[t].Action2 = Action;
	
		
	}

		//std::sort(Values.begin(), Values.end());

		for (int Rowsen = 1; Rowsen < (t + 1); Rowsen++)			//Number of Lines

		{
			Sort1 << 
				Values[Rowsen].Symbol2 << ',' <<
				Values[Rowsen].Action2
			<< "\n";
		}

		return 0;
}

The problem is that C++ doesn't know how to sort these new-fangled Value objects, since you haven't told it how. You're going to have to define what < means for Values. Someone will chime in if I'm wrong, but I believe you need to define this function:

Code:

bool operator < (const Value& lhs, const Value& rhs) {
// returns true if lhs < rhs, false otherwise
// code goes here
}

(Technically you can call it anything you want, but if you call it something else you have to specify that function in your sort call.)
This way the sort algorithm knows whether this guy is less than that one.

Yes that right ofcourse... I will check these functions out and laborate with this and see what I get... Thanks for your help !

And why do you think x.Values means anything? x is a Value -- your function declaration says so! -- so x contains a Symbol2 and an Action2. Same with y.

And of course you can call your parameters of your functions anything you like, provided they aren't keywords like if, or macros. I like to use lhs and rhs, but no one's going to complain about x and y.

Okay, so if x and y contains the Action2 and Symbol2 it makes a little bit more sense to me.

So far that I can manage right now, I think I have to specify what value in the x and y values that is interesting for sorting.. In this case Action2. So I write: x.Action2 < y.Action2
I dont know if this is correct:

Code:

bool operator < (const Value& x, const Value& y) 

 {
   return x.Action2 < y.Action2;
 };
     std::sort(Values.begin(), Values.end());

The compiler says that:
'operator <' : local function definitions are illegal
a '{' which has not yet been matched

Even if I change this line to this. Still there is something that isn&#180;t correct. The Compiler isn&#180;t happy.

Code:

{
return x.Action2 < y.Action2
};

Thank You matsp... This was the mainproblem I had. I didn&#180;t know that this function had to be ouside the main. So now it is working. Couldn&#180;t understand what was wrong... Thanks...

Yes okay I see. That was what I wondered also. I knew that Pascal could do it so I was a bit confused about it. Now I have a lot to experiment on :-)