Question

I have a method that receives a char ** as an argument in order to parse and construct a proper inner object.

  void  build (const char*  values[], const int amount=3) 
  {
       //..parse values and create instance of an inner field..
  }

It is constant, because I just want to use those values and I don’t need to modify them at all. This works pretty much fine.

Now I want to be able to code a method that returns to me a const char ** in a way that I am able to use this returned value in the previously declared method. At first, I got the values needed from the instance of my class, converted them to string and put them in an array and returned it, but it was complaining that I was returning a pointer to a local variable. So I thought of using another field to hold this pointer, I created char ** values. Then I realized that I would need to allocate the memory for the value it points to, so I went trough with it. Currently the method I’m describing looks something like:

 const char** getValues()
 {
   string var;

   var = toString(point.zone);
   values[0]= new  char[var.length()+1](); 
   strcpy(values[0], var.c_str());       

   var = toString(point.easting);
   values[1]= new char[var.length()+1]();
   strcpy(values[1],var.c_str());

   var = toString(point.northing);
   values[2]= new char[var.length()+1]();
   strcpy(values[2],var.c_str());

   return values;

 }

But at the moment this will complain because char ** values is not constant. But if I make it constant,the strcpy will complain about the opposite. If I dont return it constant then I cant us it in other function. I need help fixing this problem. Any help is deeply appreciated, thanks.

Answer 1

You got a compilation error because you try to strcpy to a char const* directly.
You should instead strcpy to a char * and assign this pointer back to the values[].

See the modified code below for a simple solution:

 const char** getValues()
 {
   string var;
   char* p;

   var = toString(point.zone);
   p = new  char[var.length()+1](); 
   strcpy(p, var.c_str());       
   value[0] = p; // now you can assign char* to char const* without compilation error

   var = toString(point.easting);
   p = new char[var.length()+1]();
   strcpy(p, var.c_str());
   value[1] = p;

   var = toString(point.northing);
   p = new char[var.length()+1]();
   strcpy(p,var.c_str());
   value[2] = p;

   return values;

 }