CODEWITHSUNDEEP
c++
ex1led
ex1led

Reputation: 469

CPP: Use of deleted function

I am trying to sort a vector that contains custom struct entries using a lambda function in c++ . But I get prompted the following error message

error: use of deleted function ‘dummy_struct& dummy_struct::operator=(const dummy_struct&)

The code looks like the following:

#include <regex>

struct dummy_struct
{
    dummy_struct(std::string name, int64_t value_a) :
        name(name),
        value_a(value_a)
    {}
    
    const std::string name;
    const int64_t value_a;
    
    int ExtractNumberFromName(std::regex key)
    {
        int retval;
        std::cmatch match;
        std::regex_search(this->name.c_str(),match,key);
        retval=std::stoi(match[0],nullptr);
        return retval;
    }
    
};


void SortByCustomKey(const std::vector<dummy_struct> collection, std::regex key)
{

    auto compare = [key](dummy_struct a, dummy_struct b)
    {
        return a.ExtractNumberFromName(key) > b.ExtractNumberFromName(key)
    };
    
    std::sort(std::begin(collection),std::end(collection),compare);

}

int main()
{

    std::vector<dummy_struct> test;
    
    test.push_back(dummy_struct("Entry[1]",1));
    test.push_back(dummy_struct("Entry[2]",2));
    test.push_back(dummy_struct("Entry[3]",3));
    
    SortByCustomKey(test,std::regex("[0-9]+"));
}

What am I missing here?

Upvotes: 0

Views: 1068

Answers (1)

Dan M.
Dan M.

Reputation: 4052

std::sort sorts vector by swapping it's elements in place.

This requires for your class to implement copy assignment operator (or move assignment), which compiler won't generate for you due to const fields in the class. For your example the only solution seems to remove the const qualifiers from the fields. If you don't want them to be modified just make them private and don't provide (public) setters. If they absolutely must stay there and you just want to get your values in sorted order you can use a different structure or store pointers in the vector.

Another solution is to write a custom swap implementation for your class that would const_cast away the qualifiers of the fields for the purpose of the assignment, although this is usually a bad code smell.

Upvotes: 3

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