在c ++中排序中不匹配'operator +'

Question

I have defined a class

class Rent
{
    public:    
    int s_time, duration, price, e_time;
    Rent(int s, int d, int p)
    {
        s_time = s;
        duration = d;
        price = p;
        e_time = s + d;
    }
    bool operator<(Rent const &r1)
    {
        return e_time < r1.e_time;
    }
};

Wished to sort it on basis of e_time , so I have defined < over Rent , however, I keep getting error

rent.cpp:38:12: error: no match for ‘operator+’ (operand types are ‘std::vector<Rent>’ and ‘int’)

     sort(R, R+n);
              ^

when I tried sort(R, R+n); . R is a vector of type Rent and n is integer(size of the vector).

Besides the above, I tried these two ways but still failed!

sort(R, R + sizeof(R)/sizeof(R[0]));
sort(R.begin(), R.end());

I googled and got some solutions with lambdas but again the second parameter to sort() is of type int + custom_datatype.

Any help would be great.

Answer 1

sort(R, R+n);
sort(R, R + sizeof(R)/sizeof(R[0]));

will not work if R is of type std::vector<Rent> . There are two problems with those lines:

1. operator+() is not defined for std::vector .
2. The compiler expects the operator<() function to be a const member function.

You can fix the operator<() function by making it a const member function.

bool operator<(Rent const &r1) const
                           //  ^^^^^
{
    return e_time < r1.e_time;
}

That still does not resolve the first problem.

However you should be able to use:

sort(R.begin(), R.end());

after that.

In theory, you shouldn't have to make the operator<() function a non- const member function. Take a look at http://en.cppreference.com/w/cpp/algorithm/sort . See the description of the comp argument. It says:

The signature of the comparison function should be equivalent to the following:

 bool cmp(const Type1 &a, const Type2 &b); 

The signature does not need to have const & , but the function object must not modify the objects passed to it.

However, not all compilers adhere to that. They expect the signature of the function to be such that they can work with const objects.

Answer 2

According to error, R is a std::vector<Rent> but following code:

sort(R, R+n);

would work only for C style array. If you want generic code that works for both C array and std::vector write it as:

std::sort( std::begin(R), std::end(R) );