sort using boost::bind

Question

bool pred(int k, int l, int num1, int num2)  
{
return (num1 < num2);
}

int main()
{
   vector <int> nums;
   for (int i=50; i > 0; --i)
   {
      nums.push_back(i);
   }
   std::sort (nums.begin(), nums.end(), boost::bind(&pred, 5, 45));
}

I am a boost newbie. I was learning to use boost::bind and I wanted to sort a vector of integers and get rid of all those elements in the vector that are greater than 45 and less than 5. Had a hard time doing it. Would be great if anyone could help me do it?

The reason I am facing problem is because I am trying to get rid of a vector element while iterating through the vector to sort it. I know it would be much easier if i sort it first and then remove elements from it. But I want to do it this way. Any help is appreciated.

Answer 1

You can't do that from sort.

Remove the elements before or after sort.

bool outOfRange(int low, int high, int num) {
    return low > num || num > high;
}

...

    nums.erase(
            std::remove_if(nums.begin(), nums.end(),
                    boost::bind(&outOfRange, 5, 45, _1)),
            nums.end()
        );

Though you really don't need boost::bind at all. Heck, we can make it a bit more generic too:

template<typename T, class cmp = std::less<T> >
struct outOfRange : std::unary_function<T, bool> {
    outOfRange(const T &low, const T &high) : low(low), high(high) {}
    bool operator()(const T &val) { return cmp()(val, low) || cmp()(high, val); }
    const T &low, &high;
}

...

    nums.erase(
            std::erase_if(nums.begin(), nums.end(), outOfRange<int>(5, 45)),
            nums.end()
        );