CODEWITHSUNDEEP
c++sorting
ejsuncy
ejsuncy

Reputation: 449

How do I use std::sort in C++?

I am using the std::sort function in <algorithm>. I followed the examples given at http://www.cplusplus.com/reference/algorithm/sort/. I want to use the example that looks like this:

// using default comparison (operator <):
   std::sort (myvector.begin(), myvector.begin()+4);

Applied to my classes, it looks like this:

std::sort(newTuples->begin(), newTuples->end());

where newTuples is of type

std::vector<Tuple>*

So I overrode the operator< function of the Tuple class:

bool const Tuple::operator<(Tuple * tup1){
    bool result = false;

    for(int iii=0; iii<tup1->size(); iii++){
        if(tup1->at(iii)->getTokensValue() < this->at(iii)->getTokensValue()){
            result = true;
            break;
        }
        else if (tup1->at(iii)->getTokensValue() > this->at(iii)->getTokensValue())
            break;
    }

    return result;


}

The problem is that when I try to build in XCode, it gives me the error shown:

Xcode error

which code snippet is in <algorithm>.

It gives me a stack trace of sorts, one line of which gives me the following:

xcode error 2

which code snippet is in my Tuple.h file.

I don't know what else to do! any help is greatly appreciated, as my CS class project is now 3 days late because I can't figure this LAST sorting algorithm out. I already implemented a Relational Database Management System with relations and the relational operations select, project, and rename. I have these tuples correctly formatted, they just need to be in sorted order. Thanks!

EDIT:

So I changed the declarations as suggested in the answers, but now it gives me:

yet another error

Any help?

Upvotes: 1

Views: 326

Answers (2)

Drew Dormann
Drew Dormann

Reputation: 63957

This compares a Tuple against a Tuple* 

bool const Tuple::operator<(Tuple * tup1)

You should change it to this:

bool Tuple::operator<( const Tuple &tup1 ) const

Upvotes: 3

Shoe
Shoe

Reputation: 76308

You need of an operator that compares const Tuple* to const Tuple*. Inside the Tuple class declare:

friend bool operator<(const Tuple*, const Tuple*);

and implement it as a regular function.

Edit

If your vector is std::vector<Tuple> then you should implement:

bool Tuple::operator<(const Tuple&) const;

instead of your pointer version.

Upvotes: 2

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