Issues with vectors and referrences

[Volatile Pulse]

I have the following code:

class Form {
   public:
      Form():
         iSize(0),
         iSelection(0),
         vFormLabels(),
         vFormExamples(),
         vFormVariables() {};
      void AddLine() {
         vFormLabels.resize(++ iSize);
         vFormExamples.resize(iSize);
         vFormVariables.resize(iSize);
      };
      void AddLine(std::string label, std::string example, std::string variable) {
         vFormLabels.push_back(label);
         vFormExamples.push_back(example);
         vFormVariables.push_back(variable);
         iSize ++;
      };

      void Play();
   private:
      unsigned int iSize;
      unsigned int iSelection;
      std::vector<std::string> vFormLabels;
      std::vector<std::string> vFormExamples;
      std::vector<std::string> vFormVariables;
};

My issue has become that I have no idea how to store the variable passed to the class member function into the vector. I read on stackoverflow that it wasn't possible, but something similar must be possible. I want to make it as easy as possible for another coder to use my class, so whatever extra code I need to learn to get this working properly is fine with me. I read about using pointers, but pointers with strings don't work very well with my assignments later on. I am also getting errors that the pointer to the string isn't valid with the passed variable.

I figure this was something simple, but I was wrong. I want the user code to look something like:

   string strName;
   string strPhone;
   string strEmail;

   Form myForm;
   myForm.AddLine("Name", "John Doe", strName);
   myForm.AddLine("Phone", "[phone]", strPhone);
   myForm.AddLine("Email", "[e-mail]", strEmail);
   myForm.Play();

What needs to be changed?

[mik2718]

I can't see anything wrong with your approach.

notes:

Do you need the void argument form of AddLine ? Maybe the other version is enough, just use empty strings to add a blank line (could be default arguments). Also the void argument AddLine has some horrible vector resizing in it.

You know that vector has a method size() giving the size of the vector, so you don't need a separate count?

In the AddLine function you are passing the strings by value, push_back then makes another copy to put in the vector. You can avoid a copy and tighten up the definition by passing the strings by const reference.

[Volatile Pulse]

What I wrote works, but not the way it's intended. I did know about the vector.size(), but the size is used for the form size, not specifically the vectors. I might change that. My issue is that the third parameter for AddLine, variable, is supposed to hold a variable by reference so that when the value is changed in the form, it will change the local variable that passed to that function, which is a reason as to why I don't want to use constants, atleast not there.

Looking at my example, the first AddLine call passes the label = "Name", the example = "John Doe", and the variable = strName. I want to be able to store a bunch of different variables in the form class vector vFormVariables so that I can change the values after the use enters their information. I can't find away around this.

And the empty call to AddLine is for future implementations of when I want to just add a blank line into the form, just to keep the form looking neat. I might change it to having default parameters, but I wrote this fairly early in the morning just to test it and the wall I ran into with is passing the reference to the variables into a vector.

[Peter87]

You can store pointers to the variables in the vector.
std::vector<std::string*> vFormVariables;

Pass variable by reference and use operator& to get a pointer to the variable that you can store in the vector.

void AddLine(std::string label, std::string example, std::string& variable) {
	vFormLabels.push_back(label);
	vFormExamples.push_back(example);
	vFormVariables.push_back(&variable);
	iSize ++;
};

[Volatile Pulse]

I get this error when I attempt to do it:

Code Blocks Compiler wrote:

C:\Programming\lib\form.h|28|error: no matching function for call to 'std::vector<std::basic_string<char>*>::push_back(const string*)'|

That was one of the things I attempted earlier, and I even made sure three times that it was exactly how you had it.

[Peter87]

Have you accidentally made variable a const reference?

[Volatile Pulse]

Yes I did accidentally. It was something I changed earlier and forgot about, but after the corrections, I run into issues with assigning strings to it. I don't know much about pointers, so I tend to have issues when I have to deal with them. This is where I get an error:
std::getline(std::cin, vFormVariables[iSelection], '\n');
And this is my error:

C:\Programming\lib\form.h|62|error: no matching function for call to 'getline(std::istream&, std::basic_string<char>*&, char)'|

[Peter87]

You have to dereference the pointer to get the string that the pointer points to.
std::getline(std::cin, *vFormVariables[iSelection], '\n');

[Volatile Pulse]

Thank you so much Peter. I don't understand why I have such a hard time with pointers when everyone makes it just look so easy. I understand the concept of them, but when it comes to applying them to usable code, I avoid them at all costs since I can't understand them.

I have made the changes to my class and am going to make it look nicer, but the rest of the code should be simple enough for me.