CODEWITHSUNDEEP
sortingc++11vectorstructconstants
YnkDK
YnkDK

Reputation: 741

C++ std::sort of const struct

I have the following struct in a vector

struct ub_node {
    const size_t index;
    const double ub_dist;
    bool operator<(const ub_node &rhs) const { return ub_dist< rhs.ub_dist; }
};

I would like to sort that vector. I have tried using std::sort but I get a compile error: error: use of deleted function ‘ub_node& ub_node::operator=(ub_node&&)’ with a reference to the line where I do std::sort(result.begin(), result.end());, where result is of type vector<ub_node>.

As far as I understand, the const does NOT affect the execution time, but merely ensures that the programmer (me) does not do anything stupid. If this is the case, I might remove the const and try to ensure that I do not change the node afterwards. Can someone confirm this? Or help me to sort it?

Upvotes: 3

Views: 836

Answers (1)

Jonathan Wakely
Jonathan Wakely

Reputation: 171303

As far as I understand, the const does NOT affect the execution time, but merely ensures that the programmer (me) does not do anything stupid.

Correct.

Sorting a vector swaps the elements around, which is not possible if the elements have immutable data (with your ub_node type you can't even remove or insert an element anywhere except the end of the vector, because that also needs to modify existing elements).

I suggest you remove the const from your members, so the type is possible to modify, and then structure your code so that parts of the program which shouldn't modify it only interacts with the class through const ub_node& or const ub_node*.

That means that the class is modifiable when necessary, but won't be modified by parts of the program that aren't supposed to modify it.

Upvotes: 3

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