I don't know if we're suppose to post non-MUD help here but... Oh well

So, I'm a pretty big noob when it comes to pointers. I just don't understand them well.

What I'm trying to do is populate a vector of pointers. HALP.

Here's my Token file.

class Token
{
public:
virtual ~Token();
virtual std::string to_string() { return typeid(*this).name(); };
};

class Operand : public Token
{
/** DON'T FORGET TO PUT PRECIDENCE ANALYZER HERE */
};

class Integer : public Operand
{
int m_value;
public:
Integer(int value) : m_value(value) { };
std::string to_string()
{
std::ostringstream oss;
oss << typeid(*this).name() << m_value;
return oss.str().c_str();
};
};

class Real : public Operand
{
double m_value;
public:
Real(double value) : m_value(value) { };
std::string to_string()
{
std::ostringstream oss;
oss << typeid(*this).name() << m_value;
return oss.str().c_str();
};
};

And my simple push_back for the vector

typedef boost::shared_ptr TokenPtr;
TokenPtr p;
p.reset( reinterpret_cast( new Integer(5) ) );
std::vector tokens;
tokens.push_back( p );

The error (bleh, linker) I get is...

LNK2019: unresolved external symbol "public: virtual __thiscall Token::~Token(void)" (??1Token@@UAE@XZ) referenced in
function "public: virtual void * __thiscall Token::`scalar deleting destructor'(unsigned int)" (??_GToken@@UAEPAXI@Z) main.obj


HALP!

...nevermind, fixed it.

virtual ~Token();

should have been

virtual ~Token() { };

Heh, yeah. For programming with Visual Studios, just google the error number (LNK2019 in this case) and msdn tends to have a helpful list of causes/solutions.

Unresolved eternal errors are caused when you declare a function but the compiler can't find or can't determine the right function definition to go with it when you call it.

The ~ function is a destructor, so even though you didn't explicitly call it, its called when an instance of the class goes out of scope, which is what caused the unresolved external.

Yeah - be great if it wouldn't let me compile at all if I have an error like that. It shouldn't wait until I call it.

It would (kinda, would slow down compiling I think), but once you know what causes the errors, they're typically really easy to fix.

:| Now I'm stuck on dereferencing the vector to get at the various pointers...

God I hate pointers

Last question for the... minute.

Is there any other way to do this besides

for(vector::const_iterator i = tokens.begin(); i != tokens.end(); ++i)
{
p = *i;
cout << p->to_string() << endl;
}

p is a boost::shared_ptr
I know, I know, for loops are the devil... Just using one to make sure it outputs the correct stuff.

...nevermind again, figured it out again

cout << i->get()->to_string() << endl;

This is embarrassing. I can do some really hard stuff, but not simple pointers.

Heh, I remember in high school they taught me pointers, and I was like "Man, thats stupid, I'll just ignore this unit, I'll never use this"

Boy was I wrong.

Though I don't know C++ (yet), I have experience with using pointers in C. For some reason, after using them enough, I grew to like them. Give them time!

Yeah, they don't bother me anymore.

:: Makes a mental note that pointers = important. ::

I understand the basics - it's when I start using them for inheritance and storing them in containers I start getting overwhelmed.

If anyone's wondering my assignment is to build a console based calculator. I'm having problems already and I'm still on the easy part!

Still no C++? Eesh!

I know C/C++ pretty well, so I could help you with some of the finer points.

For starters, you DID get a compilation error of sorts when you didn't implement your Token destructor. There's pre-compiling, compiling, and then linking. You just didn't have a problem until the final stage, but the error message is clear enough to let you know what's missing.

I don't mind pointers at all now, really. Templates, like the STL and boost, are much more of a pain, in my opinion.

You can do your code inside your for loop this way, too, if I'm not mistaken:

I know Objective C and have done a little work with C#, so I've skirted around C++ so far. I've been meaning to learn it eventually, but I've not bothered yet!

That's like...

"I can crawl, and I can run, but I can't walk for the life of me!"

Nooo, pointers are the Timtams of programming. So bad for you but oh so yummy!

Any language I use that doesn't have pointers, I get rather sad about.

Pointers!

I never bothered to learn C++ myself, why bother when you have C (which has lots of pointers in it). Good luck on your programming project.

Accelerated C++ by Andrew Koenig and Barbara E. Moo is the best beginners book I've seen for C++. It skips around all the junk you'll never use and jumps right into the important stuff.

I was impressed how it didn't mention an array but jumped right into vectors and string manipulation.

Solid read.

Night!

Except not really, since that implies that all three are mostly only different in difficulty. Other then C++ being the most commonly used of the three at the moment, there's nothing keeping you from learning C and C# without C++.