Re: C++ objects and flex

Let me try this again, before the original message disappears from the
news server...

On 11/02/2013 4:46 PM, Jorgen Grahn wrote:


OK. Fair enough. I guess my Fortran roots are showing. So let me try
again, with a little bit more of the code showing.

First, I have a complicated object class Obj, with code file Obj.cpp and
header file Obj.hpp. Let's say this consists of 5000 lines of nested
objects, and let's leave it at that. I hope I can explain the rest
without going into the details.

I then have an ObjReader class that looks like this:

ObjReader.hpp:

class ObjReader
{
   public:
     ObjReader();
     ~ObjReader();

     Obj *readObj(const std::string &objstring);

   private:
   Obj* p_obj;
}

ObjReader.cpp:

#include "ObjReader.h"

//bison function
void yygetObj(const char *objstring, Obj* obj;

//lex functions
int objlex_init(void** ptr_yy_globals);
int objlex_destroy (void* scanner );
void objset_extra (void* yyscanner );

ObjReader::ObjReader( )
{
}

ObjReader::~ObjReader()
{
     if(p_obj != NULL) delete p_obj;
     p_obj = NULL;
}

Obj* ObjReader::readObj(const std::string& objstring)
{
     if (objstring.length() > 0)
     {
         const char *ch = objstring.c_str();
         yygetObj( ch, my_obj);
     }
     return p_obj;
}//end readObj

main.cpp:

void method1(Obj* my_obj);

void main()
{
     Obj* my_obj = new Obj();
     method1(obj);
}

void method1(Obj* my_obj)
{
     ObjReader *objreader = new ObjReader();
     my_obj = objreader->readObj("some XML string");
}

I do want to get the parsing out of main, just to make the code more
structured and easier for me to read and maintain. (I did not create the
design, I just inherited it.)

My trouble is: I newed the objreader in method1, but obj is only a
pointer to the private p_obj in the objreader.

Hence I have two choices:

I do not call the ObjReader destructor in method1, and I have created a
memory leak;

I do call the ObjReader destructor in method1, and I have created a
segfault as soon as I try to do anything with my_obj outside of method1.

I suppose I can get around it by thinking passing the ObjReader into
method1, but typically there are several layers of code involved, and
sometimes even different classes that are wrapped one inside the other.
It seems unnatural to me to pass the reader, and hence I forget, leading
to all sorts of frustrations. Is there no way to make the ObjReader a
member of the Obj class? I think (hope!) that this would fix my problem.
(And yes, I think I am stuck with flex/bison for this.)