Passing variable NAME to a function

Question

Language: Visual C++, MFC

Environment: Visual Studio 2005

So I posted a similar question, but I've come to realize that I was asking the wrong question. I'm trying to use a loop to call a function on several different variables, but somewhere along the way, the program is crashing.

Simplified code is below, but I think it's actually easier to just explain it. I have a function that takes in a CString as a parameter. I have several variables I wish to feed to this function, so I put their names into an array, and I'm trying to pass them to the function that way.

// THE CODE BELOW IS WHAT I HAVE, BUT IT DOES NOT WORK //

Header File:

CString m_strTop;
CString m_strLeft;
CString m_strRight;
CString m_strBottom;

CString *var[4];

Source File: Constructor()

CString *var[4] = {
  &m_strTop
, &m_strLeft
, &m_strRight
, &m_strBottom
};

Source File: theFunction()

void myClass::DoDataExchange(CDataExchange* pDX)
{
   CSAPrefsSubDlg::DoDataExchange(pDX);

   for(int i = 2001, j = 0; i <= 2004; i++, j++)
   {
       // THE LINE BELOW IS WHERE THINGS GO WONKY, SPECIFICALLY AT &var[j]
       DDX_Text(pDX, i, *var[j]); // 'i' is the ID of the textbox
   }
} 

-- What DDX_Text expects --

void AFXAPI DDX_Text(
   CDataExchange* pDX,
   int nIDC,
   CString& value 
);

---

So like I said, I just need to feed the function the actual name of the variable. At least I think. What it's actually doing is establishing a connection between a text box in a dialog and the variable where the text box's input will be stored. I'm dereferencing correctly and everything, but I don't think this is the right approach.

Thank you for any help. And to people who answered my previous question, my apologies for misrepresenting the issue.

Answer 1

var is an array of pointers to CString .
var[j] is a pointer to CString .
&var[j] is a pointer to pointer to CString .

Now you need to pass the CString object. So you need:

DDX_Text(pDX, i, *var[j]); // dereference a pointer to CString.

Consider using std::vector instead of the C-array. It would be:

std::vector<CString> var(4);
...

DDX_Text(pDX, i, var[j]); // pass a CString object

---

I've noted that you're declaring variable var once again in the constructor:

CString *var[4] = { // this declares new temporary variable, 
                    // it doesn't initialize one from the header file
  &m_strTop
, &m_strLeft
, &m_strRight
, &m_strBottom
};

Shouldn't it be? :

var[0] = &m_strTop;
var[1] = &m_strLeft;
var[2] = &m_strRight;
var[3] = &m_strBottom;

I suppose you need the following:

// header file
class myClass
{
  std::vector<CString> var_;
  ...
};

// source file
myClass::myClass() : var_(4)
{
   ...
}

void myClass::theFunction(CDataExchange* pDX)
{
   CSAPrefsSubDlg::DoDataExchange(pDX);

   for(int i = 2001, j = 0; i <= 2004; i++, j++)
   {
       DDX_Text(pDX, i, var_[j]); // 'i' is the ID of the textbox
   }
} 

Answer 2

You're not passing the right thing into DDX_Text. It's third parameter is a reference to a CString. You're passing in the address of a pointer. So you should probably do something like

DDX_Test(pDX, i, *var[j]);