Why does this say to 'Expected '('' to a integer in cost? [duplicate]

Question

For example:

struct Spell 
{
    int id;
    vector<int> cost(4);
};

It says

'Expected parameter declaration'.

Also does this piece of code have a difference?

if (can(vector <int>inv, spell.cost)) 
{
    cout << "CAST " << spell.id << endl;
    done = true;
    break;
}

This one says

'Expected '(' for function-style cast or type construction'
        
        

Could by any chance lend me a hand?

Answer 1

As mentioned in the member initialization section in cppreference.com:

Non - static data members may be initialized in one of two ways :

1. In the member initializer list of the constructor.

   struct S
   {
       int n;
       std::string s;
       S() : n(7) {} // direct-initializes n, default-initializes s
   };
   

2. Through a default member initializer, which is a brace or equals initializer included in the member declaration and is used if the member is omitted from the member initializer list of a constructor.

   struct S
   {
       int n = 7;
       std::string s{ 'a', 'b', 'c' };
       S() {} // default member initializer will copy-initialize n, 
              // list-initialize s
   };
   

As per the above (emphasis mine), your member declaration is wrong.

I assume that, your intention was to have a vector of ints (i.e cost) as member and allocate 4 integers and default (value)initialize them .

You can fix it by either of the following ways:

1. ^✱uniform - braced initialization

   struct Spell {
       int id;
       std::vector<int> cost{ std::vector<int>(4) };
       //                  ^^^                  ^^^^
   };
   

2. equals initializer

   struct Spell {
       int id;
       std::vector<int> cost =  std::vector<int>(4); // or decltype(cost)(4)
       //                   ^^^^^^^^^^^^^^^^^^^^^^^^
   };
   

3. provide a constructor and in constructor member initializer

   struct Spell { 
       int id; 
       std::vector<int> cost;
       Spell()
           : cost(4) // constructor member initializer
       {} 
   };
   

^✱Since std::vector has the std::initializer_list constructor, unfortunately you can not write std::vector<int> cost{ 4 }, as it will be interpreted, the 4 being a single vector element.