Unexpected End of File

I note that ashvisitor and ash include each other -- this could be a problem.

you're using the ideitifier AST both a class name and a namespace. This is certainly not going to work, althopugh there are probably other problems in the code.

I cant tell you how it all works, but I can tell you that include guards are not always going to work here. We did this accidentally last project, and as was mentioned, a forward decl fixed our problems and the circular includes were avoided. Our stuff had include guards but would not compile, I forget what errors it 'created' to explain its problems.

Eureka! your project probably uses the infamous "precompiled headers" option. Disable it, and remove the "stdafx.h" header from it.

Check for unblanaced #ifndef and #endif pais in all your header files. Also, try to see what happens when you remove these directives althogether. Finally, try to collapse the two class headers into one header file. Decalre both classes in it and see if this solves the problem. Later you can split it again.

Ok, I tried combining all the files into a single .h file and it worked. Then I split them apart without the #ifndef ... #endif stuff and it worked, but as soon as I put the #ifndef stuff in, it fails. I put in #error directives in else clauses to check to see if something was being included twice, but none of them are. My files are:
AST.h
#ifndef __AST_H__
#define __AST_H__

class ASTVisitor;

class AST {
public:
virtual void process(ASTVisitor &visitor) = 0;
};
#else
#error FAIL

#endif
ASTVisitor.h
#ifndef __AST_VISITOR_H__
#define __AST_VISITOR_H__
class BooleanConstant;

class ASTVisitor {
protected:
ASTVisitor();

public:
/** Constant Constructions **/
virtual void forBooleanConstant(BooleanConstant *boolConst) = 0;
};

#else
#error FAIL
#endif
BooleanConstant.h (it turns out that I have to include AST.h in this file otherwise the compiler complains that it doesn't know about the base class AST even when I just put a forward declaration)
#ifndef __BOOLEAN_CONSTANT_H__
#define __BOOLEAN_CONSTANT_H__

#include "AST.h"

class BooleanConstant : public AST {
private:
bool _value;
static BooleanConstant _TRUE;
static BooleanConstant _FALSE;

public:
bool getValue();
virtual void process(ASTVisitor &visitor);

protected:
BooleanConstant(bool value);
virtual ~BooleanConstant();
public:
static const BooleanConstant* forValue(bool b);
};

#else
#error FAIL
#endif
And BooleanConstant.cxx
#include "BooleanConstant.h"
#include "ASTVisitor.h"

BooleanConstant::BooleanConstant(bool b) {
_value = b;
}

BooleanConstant::~BooleanConstant() {
}

void BooleanConstant::process(ASTVisitor &visitor) {
visitor.forBooleanConstant(this);
}

const BooleanConstant* BooleanConstant::forValue(bool b) {
if( b ) {
return &BooleanConstant::_TRUE;
} else {
return &BooleanConstant::_FALSE;
}
}

Any ideas as to why this might happen? Thanks a lot for all your help.

///AST.h
#ifndef __AST_H__
#define __AST_H__

class ASTVisitor;

class AST {
...

///ASTVisitor.h
#ifndef __AST_VISITOR_H__
#define __AST_VISITOR_H__

#include "AST.h"
class BooleanConstant;

class ASTVisitor {
...

///booleanConstant.h
#ifndef __BOOLEAN_CONSTANT_H__
#define __BOOLEAN_CONSTANT_H__

#include "ASTVisitor.h"

class BooleanConstant : public AST {
...

///BooleanConstant.cpp
#include "BooleanConstant.h"

BooleanConstant::BooleanConstant(bool b) {
_value = b;
}
...

gcc did compile this.
only 2 linking problems undefined reference to `BooleanConstant::_TRUE'
...

Using C++ BuilderX, I didn't encounter this error but I ecnountered many other compilation errros which pertain to syntax errors. First, in one of the declarations of BooleanConstant::forValue you have a syntax error. You declare it:
BooleanConstant::BooleanConstant *forValue()

instead of
BooleanConstant * BooleanConstant::forValue();

This isn't all: I don't see why you need this class in the first place. Worst yet, you're using the symbols TRUE and FALSE as variables names which is a very bad idea because I'm almost certain that every compiler these days still retains these names as macros from the pre-bool era, which might explain why the preprocessor chokes. Finally, I don't see why a class called BooleanConstants should have a base class. Notice also:

public:
static bool* forValue(bool b);
};

you declare here a static member function that returns a non static member called _b. This is illegal.

In short, what I suugest is that you simplify this project, remove all instances of "over-engineering" (such as having a class whose sole purpose is to return a bool variable, using static data members as constants instead of using the keywords true and false etc.) and then compile this project. VS 2003 isn't a perfect compiler but I'm sure it can hjandle three header files.
The fact that GCC compiled this code doesn't promise much. You got linkage errors which suggest that something isn't defined in the project, hence, you still have to add definitions of the static data members (you only declare them).

OK, using these modified source files (precisely) with C++ BuilderX, everything compiles and links just fine. Evlich, try to use these files and make sure that your compiler doesn't sneak in its usual follies: precopiled headers and "stdafx.h". Note also that I added main() to the .cpp file.
mr1yh1, does this project compile under GCC?

1:
#ifndef __AST_H__
#define __AST_H__

class ASTVisitor;

class AST {
public:
virtual void process(ASTVisitor &visitor) = 0;
};

#endif
2:
#ifndef __AST_VISITOR_H__
#define __AST_VISITOR_H__
class BooleanConstant;

class ASTVisitor {
protected:
ASTVisitor();

public:
/** Constant Constructions **/
virtual void forBooleanConstant(BooleanConstant *boolConst) = 0;
};

#endif

3:

#ifndef __BOOLEAN_CONSTANT_H__
#define __BOOLEAN_CONSTANT_H__

class BooleanConstant : public AST {
private:
bool _value;
static BooleanConstant _TRUE;
static BooleanConstant _FALSE;

public:
bool getValue();
virtual void process(ASTVisitor &visitor);

protected:
BooleanConstant(bool value);
virtual ~BooleanConstant();
public:
static const BooleanConstant* forValue(bool b);
};

#endif

4:

#ifndef __BOOLEAN_CONSTANT_CXX__
#define __BOOLEAN_CONSTANT_CXX__

#include "AST.h"
#include "ASTVisitor.h"
#include "BooleanConstant.h"

BooleanConstant::BooleanConstant(bool b) {
_value = b;
}

BooleanConstant::~BooleanConstant() {
}

void BooleanConstant::process(ASTVisitor &visitor) {
visitor.forBooleanConstant(this);
}

const BooleanConstant* BooleanConstant::forValue(bool b) {
if( b ) {
return &BooleanConstant::_TRUE;
} else {
return &BooleanConstant::_FALSE;
}
}

int main()
{}
#endif

i edited post a lot of times becos of wrong copy paste. :D

yes it compilied.
same 2 link errors:
undefined reference to `BooleanConstant::_TRUE'
..

No I used it with once .cpp file that has main() in it. The linkage errors are not a problem at the moment because they are quite expected: the program doesn't define the static data members TRUE and FALSE, it only delcares them which is of course an error, but the original problem was getting the sources to compile.

You have to #include .h files. Simply creating them does nothing. Adding them to the project also does nothing, or at most it checks the syntax.

place the curson after the last character you typed in the header file and hit enter to insert a newline character

Then your problem is you have a setup that does partial compiles (it thinks it knows what has changed and only re-compiles those files). Just do a "rebuild all" from your IDE, extra end of lines works(usually) but you might miss a file and it takes way too long.