Syntax error in map instantiation.. probably something silly :)

Here's the code with the errors...

Code:

---

#ifndef DATABASE_H
#define DATABASE_H

#include "Object.h"
#include <map>
#include <iostream>
#include <boost/shared_ptr.hpp>
#include <string>
#include <vector>

class Database
{
public:       

        std::map<std::string name, std::vector<boost::shared_ptr<T>> Data;
        typedef boost::weak_ptr<Data> Data_Observer;
        // Function to access a specific manager within the map
        Data_Observer Access_Manager(std::string Filename)
        {
                Manager_Map::iterator it = Database_Manager.find(Filename);
                // check if the manager exists in the map
                if (it == Database_Manager.end())
                {
                        // if not throw an error
                        std::cout << "Manager does not exist!" << std::endl;
                }
                else
                {
                        // if so return a pointer to the manager
                        return Data_Observer(it->second);
                }
        }

        //Save a manager completely to a file
        void Save_to_File(std::string Filename, std::map<std::string name, std::vector<boost::shared_ptr<T_>>)
        {
                std::ofstream ofs(Filename.c_str());
                boost::archive::text_oarchive oa(ofs);
        // write class instance to archive
        oa << Data;
                Data.~Object_Manager();
            // archive and stream closed when destructors are called
        }

        // Load a manager from a file and add it to the list of managers
        void Read_File(std::string Filename, Object_Manager * Data)
        {
        // create and open an archive for input
        std::ifstream ifs(Filename.c_str(), std::ios::binary);
        boost::archive::text_iarchive ia(ifs);
        // read class state from archive
        ia >> Data;
                // create a pointer to the data
                Manager_Ptr Raw_Manager(Data);
                // pair the filename with the manager typ for easy access
                Database_Manager.insert(std::make_pair(Filename, Raw_Manager));
        // archive and stream closed when destructors are called
        }
private:
        Manager_Map Database_Manager;
};

#endif

---

And here are the errors... theres on "fatal" error that it can't recover from, I have never seen this before...

Code:

---

------ Build started: Project: TextGame, Configuration: Debug Win32 ------
Compiling...
Main.cpp
c:\documents and settings\home\my documents\visual studio 2005\projects\textgame\textgame\database.h(15) : error C2146: syntax error : missing ',' before identifier 'name'
c:\documents and settings\home\my documents\visual studio 2005\projects\textgame\textgame\database.h(15) : error C2065: 'name' : undeclared identifier
c:\documents and settings\home\my documents\visual studio 2005\projects\textgame\textgame\database.h(15) : error C2065: 'T' : undeclared identifier
c:\documents and settings\home\my documents\visual studio 2005\projects\textgame\textgame\database.h(15) : error C3203: 'shared_ptr' : unspecialized class template can't be used as a template argument for template parameter '_Ty', expected a real type
c:\documents and settings\home\my documents\visual studio 2005\projects\textgame\textgame\database.h(15) : error C2146: syntax error : missing ',' before identifier 'Data'
c:\documents and settings\home\my documents\visual studio 2005\projects\textgame\textgame\database.h(15) : error C2065: 'Data' : undeclared identifier
c:\documents and settings\home\my documents\visual studio 2005\projects\textgame\textgame\database.h(15) : error C2143: syntax error : missing '>' before ';'
c:\documents and settings\home\my documents\visual studio 2005\projects\textgame\textgame\database.h(15) : error C2208: 'std::map' : no members defined using this type
c:\documents and settings\home\my documents\visual studio 2005\projects\textgame\textgame\database.h(15) : fatal error C1903: unable to recover from previous error(s); stopping compilation
Build log was saved at "file://c:\Documents and Settings\Home\My Documents\Visual Studio 2005\Projects\TextGame\TextGame\Debug\BuildLog.htm"
TextGame - 9 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

---

So yeah, any ideas? as far as I know I initialized everything right, except maybe the template portion for the shared pointers....

Thanks for the help already :)

std::map<std::string name, std::vector<boost::shared_ptr<T>> Data;

Separate the >> at the end with a space or it gets interpreted as the shift operator

void Save_to_File(std::string Filename, std::map<std::string name, std::vector<boost::shared_ptr<T_>>)

here too.

Okay, thanks for that tip, but I'm getting all the same errors :(

New code:

Code:

---

#ifndef DATABASE_H
#define DATABASE_H

#include "Object.h"
#include <map>
#include <iostream>
#include <boost/shared_ptr.hpp>
#include <string>
#include <vector>

class Database
{
public:       

        std::map<std::string name, std::vector<boost::shared_ptr<T> > Data;
        typedef boost::weak_ptr<Data> Data_Observer;
        // Function to access a specific manager within the map
        Data_Observer Access_Manager(std::string Filename)
        {
                Manager_Map::iterator it = Database_Manager.find(Filename);
                // check if the manager exists in the map
                if (it == Database_Manager.end())
                {
                        // if not throw an error
                        std::cout << "Manager does not exist!" << std::endl;
                }
                else
                {
                        // if so return a pointer to the manager
                        return Data_Observer(it->second);
                }
        }

        //Save a manager completely to a file
        void Save_to_File(std::string Filename, Data)
        {
                std::ofstream ofs(Filename.c_str());
                boost::archive::text_oarchive oa(ofs);
        // write class instance to archive
        oa << Data;
                Data.erase();
            // archive and stream closed when destructors are called
        }

        // Load a manager from a file and add it to the list of managers
        void Read_File(std::string Filename, Data)
        {
        // create and open an archive for input
        std::ifstream ifs(Filename.c_str(), std::ios::binary);
        boost::archive::text_iarchive ia(ifs);
        // read class state from archive
        ia >> Data;
                // create a pointer to the data
                Data_Observer Raw_Manager(Data);
                // pair the filename with the manager typ for easy access
                Database_Manager.insert(std::make_pair(Filename, Raw_Manager));
        // archive and stream closed when destructors are called
        }
private:
        Manager_Map Database_Manager;
};

#endif

---

Quote:

---

Originally Posted by Shamino

Code:

---

std::map<std::string name, std::vector<boost::shared_ptr<T>> Data;

---

---

Remove "name"

EDIT: Also, what is T? Is your Database class supposed to be template <typename T> ?

Sweet, I should have caught that, thanks. 7 more errors....

But this is really a question of what I'm trying to do...

Code:

---

------ Build started: Project: TextGame, Configuration: Debug Win32 ------
Compiling...
Main.cpp
c:\documents and settings\home\my documents\visual studio 2005\projects\textgame\textgame\database.h(15) : error C2065: 'T' : undeclared identifier
c:\documents and settings\home\my documents\visual studio 2005\projects\textgame\textgame\database.h(15) : error C3203: 'shared_ptr' : unspecialized class template can't be used as a template argument for template parameter '_Ty', expected a real type
c:\documents and settings\home\my documents\visual studio 2005\projects\textgame\textgame\database.h(15) : error C2146: syntax error : missing ',' before identifier 'Data'
c:\documents and settings\home\my documents\visual studio 2005\projects\textgame\textgame\database.h(15) : error C2065: 'Data' : undeclared identifier
c:\documents and settings\home\my documents\visual studio 2005\projects\textgame\textgame\database.h(15) : error C2143: syntax error : missing '>' before ';'
c:\documents and settings\home\my documents\visual studio 2005\projects\textgame\textgame\database.h(15) : error C2208: 'std::map' : no members defined using this type
c:\documents and settings\home\my documents\visual studio 2005\projects\textgame\textgame\database.h(15) : fatal error C1903: unable to recover from previous error(s); stopping compilation
Build log was saved at "file://c:\Documents and Settings\Home\My Documents\Visual Studio 2005\Projects\TextGame\TextGame\Debug\BuildLog.htm"
TextGame - 7 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

---

I'm trying to make it so I can pass a map like that to one of my functions, only the shared pointer needs to be templated because I'm not sure exactly what I'm going to pass the function to save, or load.

I suppose I need to make a templated function... but can someone help me with this?

Quote:

---

Originally Posted by Shamino

I'm trying to make it so I can pass a map like that to one of my functions, only the shared pointer needs to be templated because I'm not sure exactly what I'm going to pass the function to save, or load.

---

But if you don't know the type (T) you can't instantiate an object. As it is now, you are trying to create one of these map objects in the Database class. You simply can't do that if you don't know what T is.

Without knowing a lot more about how all this is supposed to work, I can't really suggest a fix.

yeah I was just kinda testing out syntax, and failing horribly, I know I can't instantiate that map unless I know what T is, so I'll leave that up to other processes. But making a function be able to accept an ambiguous type is what I'm curious about.

Quote:

---

Originally Posted by Shamino

yeah I was just kinda testing out syntax, and failing horribly, I know I can't instantiate that map unless I know what T is, so I'll leave that up to other processes. But making a function be able to accept an ambiguous type is what I'm curious about.

---

Then you need to make that function a template. For example, a function that can work on std::vectors of any type T:

Code:

---

template <typename T>
void do_work(std::vector<T> &vec)
{
    // do something to vec
}

---

In modern C++ you can have template member functions and template constructors, also.

Sweet, gotta love modern C++ then..

Originally, I had my data objects setup so they *all* derived from a single object base class, I found that this had alot of type safety issues, so I decided to switch to templates, templates are a bit iffy in my realm of C++ knowledge but this should work better when it's finished.

All the database class does is take a map of strings and shared pointers of an ambiguous type, attach a name to it, and write it to a file for later loading. I use weak pointers to observe the data via a vector of shared pointers to the maps, I think this will work just fine.

Quote:

---

Originally Posted by Shamino

All the database class does is take a map of strings and shared pointers of an ambiguous type, attach a name to it, and write it to a file for later loading.

---

Note that this doesn't mean you can store any kind of shared pointer in a given map, though. You can only store shared pointers to type T. T can be any type, but each individual container can only contain a single type.

If you really want to hold pointers to ANY kind of objects all in the same map, there's no other way but to use runtime polymorphism (i.e., the way you were doing it, with a common base class and virtual functions).

You mean I can't have a vector of pointers of maps of any typename?

uh oh...

Quote:

---

Originally Posted by Shamino

You mean I can't have a vector of pointers of maps of any typename?

---

To be clear, what you're asking for is a map that maps strings to pointers to all kinds of different objects? Different types of objects but all in the same map?

You can do it, but the map isn't a template anymore, it just holds pointers to the base type:

Code:

---

std::map<std::string name, std::vector<boost::shared_ptr<base_class> > >

---

Then, all types that might be in the map have to inherit from base_class.

No, not all in the same map.

The vector is the unifying data type, it points to these maps that I create which are ambiguous, is this possible?

you see, if I use a base class like object for all my data, I was told it would be very very bad for type safety

Quote:

---

Originally Posted by Shamino

No, not all in the same map.

The vector is the unifying data type, it points to these maps that I create which are ambiguous, is this possible?

---

I'm not sure what you mean here. Can you explain what you WANTED "T" to be in your original example?

Quote:

---

you see, if I use a base class like object for all my data, I was told it would be very very bad for type safety

---

I'm not sure why somebody would tell you that. It sounds like what you want is polymorphism. There's no sense in trying to emulate polymorphism instead of just using it.

T could be a menu object, or a sound object, or a string object, yknow for long text portions in a text game. I want to organize all these data types in a centralized class, Database.

If I use polymorphism here, it could be the end of my program if I try to use a sound file as a text file, know what I mean? If I use templates and return the actual specific data type, it prevents that problem, so stupid programmers don't try to add something to my system that will break it, not that they could know, and that is exactly the problem, they wouldn't know.

Ogre3d does this and it is one of the main flaws of their engine. People try to program for ogre and end up breaking things because they accidentally grab a sound file and try to output it as a 3d model on the screen.

It's really not a big big problem, but I'd rather do it this way, the type safe way.

I want to have a vector in the database class, which points to maps, which are of type std::string/T, is that possible?

Quote:

---

Originally Posted by Shamino

If I use polymorphism here, it could be the end of my program if I try to use a sound file as a text file, know what I mean? If I use templates and return the actual specific data type, it prevents that problem, so stupid programmers don't try to add something to my system that will break it, not that they could know, and that is exactly the problem, they wouldn't know.

---

But templates don't work at runtime. You can't use a template unless the compiler can determine AT COMPILE TIME what the type T is. You want something more dynamic than that. You need to use runtime polymorphism.

I'm not sure why you were told that polymorphism isn't type-safe. It's one of the basic driving features of the C++ language. You would never "try to use a sound file as a text file" if you design your library correctly.

Quote:

---

Ogre3d does this and it is one of the main flaws of their engine. People try to program for ogre and end up breaking things because they accidentally grab a sound file and try to output it as a 3d model on the screen.

---

It sounds like that program is just badly coded, then.

Quote:

---

It's really not a big big problem, but I'd rather do it this way, the type safe way.

---

It can't be done this way because the compiler doesn't know what "T" is. You are asking "T" to stand for some type that can only be determined at runtime. A template just can't do that.

Man that guy was really convincing that I could do it this way, and it would be better... Maybe he really knew less than I did....

But I agree, my argument was the same.

Why would I try to use a sound file as a text file ever?

Quote:

---

Originally Posted by Shamino

Why would I try to use a sound file as a text file ever?

---

Sounds like the code in question has a lot of pointers to the base class being passed around. Really, the only purpose of the base class is to let you stuff all these different types into the same map.

The basic architectural issue is, how do you get stuff out of the map in a type-safe way? If you design it so that the caller asks for something by name, and a base class pointer is handed back, you have the problem of determining what the actual type of that object is. But by accessing the database a different way you can get around this problem.

Instead of having the DB return a pointer, you call the lookup and pass it a pointer to an "acceptor" object which accepts the looked-up pointer via a function call. This leaves the decision about what type of object it is UP TO THE OBJECT ITSELF, because it will invoke the proper accept function on the acceptor object:

Code:

---

// abstract Acceptor base class -- classes interested in looking things up from a database
// will derive from this.
class Acceptor
{
public:
    virtual ~Acceptor() { }
    virtual bool acceptSound(DBSoundObject *ptr) = 0;
    virtual bool acceptText(DBTextObject *txt) = 0;
};

// Database object base class -- all objects stored in the database derive from this and
// override the put() method to call the appropriate acceptor function.
class DBObject
{
    virtual ~DBObject { }
    virtual bool put(Acceptor *acc) { return false; }
};

class DBSoundObject : public DBObject
{
public:
    bool put(Acceptor *acc)
    {
        return acc->acceptSound(this);
    }
};

class DBTextObject : public DBObject
{
public:
    bool put(Acceptor *acc)
    {
        return acc->acceptText(this);
    }
};

---

Now, the things you store in the maps are shared pointers to DBObject objects. To do a lookup, you get the DBObject from the map, then you call its put() method and pass a pointer to the Acceptor object, i.e., the object which was trying to do the lookup.

Code:

---

DBObject *obj = some_map[some_string];
if(obj)
{
    // Get the result and pass it to this, which accepts it with one of the various acceptor
    // functions
    obj->put(this);
}

---

Or, if you know for sure that obj will never come back null, the more compact:

Code:

---

some_map[some_string]->put(this);

---

It seems sort of roundabout, but you should be able to see that there is no way an object could ever be treated as the wrong type, because the object itself knows what its type is, and the object decides which accept() method to call on the Acceptor.

So you derive from Acceptor and override the various accept() functions to accept the lookup-up objects and do whatever needs to be done with them.

That is some interesting C++ design, never seen it before, but it looks great, I'll consider this more when my AC is turned off, it's kinda freezing cold while im typing on the computer :\

Quote:

---

Originally Posted by Shamino

That is some interesting C++ design, never seen it before, but it looks great, I'll consider this more when my AC is turned off, it's kinda freezing cold while im typing on the computer :\

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I goofed when using some names in my example code... I fixed it and highlighted the changes in blue.