CODEWITHSUNDEEP
c++
John
John

Reputation: 193

What my customized compare does not work?

I wrote a compare operator as below:

struct GreaterThan
{
    bool operator() (string a, string b)
    {

        if (a.length() == 1 && a[0] == b[0]) //LINE1
        {
            return true;
        }

        if (b.length() == 1 && b[0] == a[0]) //LINE2
        {
            return true;
        }

        return a.compare(b) == 1 ? true : false;
   }
};

vector<string> v{"2", "20", "5", "7"};
sort(v.begin(), v.end(), GreaterThan());

The purpose of LINE1 and LINE2 is to make "2" ahead of "20" when sorting. But it causes runtime error. The error is "invalid operator<" on visual studio.

Upvotes: 0

Views: 54

Answers (1)

R Sahu
R Sahu

Reputation: 206567

The return value of std::string::compare doesn't have to be 1 when a is "greater than" b. It just has to be greater than 0.

Instead of 

return a.compare(b) == 1 ? true : false;

I think you need:

return (a.compare(b) < 0);

Upvotes: 1

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