Structures in C#

Question

I am using a structure in my program as below:

public struct chromo_typ
{
        public string   bits;  
        public float    fitness;

        chromo_typ(string bts, float ftns)
        {
            bits = bts;
            fitness = ftns;
        }
};

I am using the constructor defined in the struct i.e. chromo_typ(string bts, float ftns) in my main(). My main() contains the following code:

chromo_typ[] temp = new chromo_typ[VM_Placement.AlgorithmParameters.pop_size];

                    chromo_typ ct = new chromo_typ();

                    int cPop = 0;

                    //loop until we have created POP_SIZE new chromosomes
                    while (cPop < VM_Placement.AlgorithmParameters.pop_size)
                    {
                        // we are going to create the new population by grabbing members of the old population
                        // two at a time via roulette wheel selection.
                        string offspring1 = p.Roulette(TotalFitness, Population);
                        string offspring2 = p.Roulette(TotalFitness, Population);

                        //add crossover dependent on the crossover rate
                        p.Crossover(offspring1, offspring2);

                        //now mutate dependent on the mutation rate
                        p.Mutate(offspring1);
                        p.Mutate(offspring2);

                        //add these offspring to the new population. (assigning zero as their
                        //fitness scores)
                        temp[cPop++] = ct.chromo_typ(offspring1, 0.0f);
                        temp[cPop++] = ct.chromo_typ(offspring2, 0.0f);

                    }//end loop

I am getting the following error at temp[cPop++] = ct.chromo_typ(offspring1, 0.0f); and temp[cPop++] = ct.chromo_typ(offspring2, 0.0f);

Error: 'VM_Placement.Program.chromo_typ' does not contain a definition for 'chromo_typ' and no extension method 'chromo_typ' accepting a first argument of type 'VM_Placement.Program.chromo_typ' could be found (are you missing a using directive or an assembly reference?)

Am I using structure incorrectly? How can I resolve this?

You forgot to use the *new* keyword. A constructor is not a method. — Hans Passant, Apr 22 '12 at 19:42
Did you mean `temp[cPop++] = new chromo_typ(offspring1, 0.0f);` ? — harold, Apr 22 '12 at 19:43
Tried using 'new' keyword i.e. my constructor calling syntax now is "temp[cPop++] = new chromo_typ(offspring1, 0.0f);" but I am getting this error now "'VM_Placement.Program.chromo_typ' does not contain a constructor that takes 2 arguments" — user1277070, Apr 22 '12 at 19:47
But I do have a constructor taking 2 arguments in my structure... — user1277070, Apr 22 '12 at 19:48

score 5 · Accepted Answer · answered Apr 22 '12 at 19:43

5

In this case, chromo_typ is a constructor, but you are calling it as an instance method. Constructors are used to construct an object, i.e.,

temp[cPop++] = new chromo_typ(arg1, arg2);

It is not a method that you can call on an instance of your type.

On a side note, the canonical way to name types in C# is to use start with an uppercase letter and use camel case, i.e.,

public struct ChromoTyp { }

Of course, this is not a rule, but it is usually a good idea to follow the patterns already in use by the community.

answered Apr 22 '12 at 19:43

Ed S.

122,712
22
185
265

Yes I know its a constructor, but so how do I make a call to that constructor? I need to create the structure object right? – user1277070 Apr 22 '12 at 19:44
@user1277070: I gave you an example. You must use the `new` keyword. – Ed S. Apr 22 '12 at 19:45
Hey I tried using 'new' keyword as the same way in your example... but now I am getting this error: "VM_Placement.Program.chromo_typ' does not contain a constructor that takes 2 arguments" – user1277070 Apr 22 '12 at 19:49
My syntax is "temp[cPop++] = new chromo_typ(offspring1, 0.0f);" – user1277070 Apr 22 '12 at 19:49
Could it be because I am assigning it to an array of chromo_typ i.e. temp[cPop++] is of type chromo_typ "chromo_typ[] temp = new chromo_typ[VM_Placement.AlgorithmParameters.pop_size];" ?? – user1277070 Apr 22 '12 at 19:51
2

@EdS. it looks like his constructor is private, no? – Mike Park Apr 22 '12 at 19:53
@climbage - I made the constructor public and the error went off... but by default everything in a structure is public right? – user1277070 Apr 22 '12 at 19:55
@user1277070 in C++ maybe--C# is going to be a little different – Mike Park Apr 22 '12 at 19:57
@user1277070 See http://stackoverflow.com/questions/8479214/any-reason-to-write-the-private-keyword-in-c for more info on default visibility – Mike Park Apr 22 '12 at 19:59
yes in C++ it is... so I thought it would be same for C# as well... anyways Thank you all for instant help... I appreciate it!! – user1277070 Apr 22 '12 at 19:59
@climbage: So it is, I missed that. – Ed S. Apr 22 '12 at 21:52

Structures in C#

1 Answers1