Question

I have a constructor, that receives a character pointer. If it is empty, I need to set its member variable to NULL, however, the program crashes on exit when I try to.

I have verified that it gets to the line where it sets it to NULL and that is the cause of the crash.

I’ve tried the following:

val = NULL;

val = 0;

val = "";

Those all cause a crash, however if I used:

val = new Char[1];
val = "o";

it didn’t crash.

Is there something that I’m not doing?

Update:

Here is a quick update to my problem.

The destructor I’m using is:

~LField() { 
    if (val)
      delete[] val;
}

If I take out:

if (val)
  delete[] val;

then the program doesn’t crash on exit with:

val = "";

Here is some more code as requested:

LField(int rowNumVal, int colNumVal, int widthVal, const char *valVal = "", bool canEditVal = true) { 
    if(strlen(valVal) > 0) {            
      //doesn't jump in here since valVal is empty
    }
    else {
      val = ""; // this is where I'm trying to set a NULL value
    }
}

LField(const LField &clone) { 
  if (val)
    delete[] val;

  val = new char[strlen(clone.val)]; 
  strcpy(val, clone.val);
  rowNum = clone.rowNum;
  colNum = clone.colNum;
  width = clone.width;
  canEdit = clone.canEdit;
  index = clone.index;
}

LField& operator=(const LField &lfieldobj) {
    if (this != &lfieldobj) {
    if (val)
       delete[] val;

    val = new char[strlen(lfieldobj.val)];
    strcpy(val, lfieldobj.val);
    rowNum = lfieldobj.rowNum;
    colNum = lfieldobj.colNum;
    width = lfieldobj.width;
    canEdit = lfieldobj.canEdit;
    index = lfieldobj.index;
   }

   return *this;
}

Modified:

LField(int rowNumVal, int colNumVal, int widthVal, const char *valVal = NULL, bool canEditVal = true) { 
    if(valVal != NULL) {            

    }
    else {
      val = NULL; 
    }
}

LField(const LField &clone) { 
  delete[] val;
  if (clone.val != NULL) {
     val = new char[strlen(clone.val) + 1]; 
     strcpy(val, clone.val);
  }
  else
    val = NULL;
  rowNum = clone.rowNum;
  colNum = clone.colNum;
  width = clone.width;
  canEdit = clone.canEdit;
  index = clone.index;
}

LField& operator=(const LField &lfieldobj) {
    if (this != &lfieldobj) {
       delete[] val;
    if (lfieldobj.val != NULL) {                
       val = new char[strlen(lfieldobj.val) + 1];
       strcpy(val, lfieldobj.val);
    }
    else
       val = NULL;
    rowNum = lfieldobj.rowNum;
    colNum = lfieldobj.colNum;
    width = lfieldobj.width;
    canEdit = lfieldobj.canEdit;
    index = lfieldobj.index;
   }

   return *this;
}

~LField() { 
      delete[] val;
}

I’ve updated the code. Now val is either allocated memory with new[] or it is NULL, so there shouldn’t be a problem with delete[]. However, it still crashes on exit.

Answer 1

In the copy constructor you try to delete[] an uninitialized pointer:

LField(const LField &clone) { 
  //good code here, then...
  if (val) //<+ some random address here
    delete[] val;//<-undefined behavior
}

just don’t do that, skip the whole construct. The copy constructor is invoked on an unitilialized object, there’re no resources to “free” yet.

Also you try to delete[] a string literal, that’s undefined behavior. Try the following change:

LField(int rowNumVal, int colNumVal, int widthVal, const char *valVal = "", bool canEditVal = true) { 
    if(strlen(valVal) > 0) {            
      //doesn't jump in here since valVal is empty
    }
    else {
      val = new char[1];
      *val = 0;
    }
}

also the following is a buffer overrun:

val = new char[strlen(whatever)];  <-forgot to +1 for the null terminator
strcpy(val, whatever);

also checking for a null pointer before delete[] is unnecessary – delete[] on a null pointer is legal and has no effect.