I've looked this up and the closest thing I found was this except I don't have any forward declarations. I only have one pure virtual function in the base class which I'm implementing in the subclass as follows:
Command.h
#ifndef _COMMAND_H_
#define _COMMAND_H_
#include <string>
#include "Stack.h"
#include "Number.h"
class Command
{
public:
std::string cmdType;
Command(void);
Command (std::string cmdType);
virtual void executeCommand(Stack<Number> & stack) = 0;
~Command (void);
};
#endif // !defined _COMMAND_H_
Command.cpp
Command::Command(void)
:cmdType("")
{}
Command::Command(std::string cmdType)
:cmdType(cmdType)
{}
Command::~Command(void)
{}
Number.h
#ifndef _NUMBER_H_
#define _NUMBER_H_
#include "Command.h"
#include "Stack.h"
class Number : public Command
{
public:
Number (float num);
void executeCommand(Stack<Number> & stack);
float val;
~Number (void);
};
#endif // !defined _NUMBER_H_
Number.cpp
#include "Number.h"
Number::Number(float num)
:val(num)
{
cmdType = "hi";
}
void Number::executeCommand(Stack<Number> & stack)
{
stack.push((*this));
}
File error occurs:
Error 4 error C2259: 'Number' : cannot instantiate abstract class c:\...\add.cpp 34
Add.cpp
#include "Add.h"
Add::Add(void)
:Binary("+")
{
}
Add::~Add(void)
{
}
void Add::executeCommand(Stack<Number> & numStack)
{
Number num1 = numStack.top(); //THIS LINE HAS THE ERROR
numStack.pop();
Number num2 = numStack.top();
numStack.pop();
float tempVal = num2.val + num1.val;
num1.val = tempVal;
numStack.push(num1);
}
Add.h
#ifndef _ADD_H_
#define _ADD_H_
#include "Stack.h"
#include "Number.h"
#include "Binary.h"
class Add : public Binary
{
public:
Add (void);
void executeCommand (Stack<Number> & numStack);
~Add (void);
};
#endif // !defined _ADD_H_
This is a circular dependency problem.
Command.h includes Number.h
Number.h includes Command.h
Usually it is solved by replacing one of the includes with a forward declaration, try forward-declaring Number in Command.h instead of including Number.h; move that include to Command.cpp.
Related
I have these files structure:
main.cpp
#include "main.h"
Map map;
Fruit fruit;
Stone stone;
main.h
extern Map map;
extern Fruit fruit;
extern Stone stone;
map.h
#include "main.h"
class Map {public: int size = 20;};
fruit.h
#include "main.h"
class Fruit { public: int pos = 1; draw() {return map.size;} };
stone.h
#include "main.h"
class Stone { public: draw() {return map.size * fruit.pos;} };
The problem is when I'm trying to use map.size and fruit.pos I get error:
'map': undeclared identifier
The same with stone. So, what's wrong?
main.h should include map.h not the other way around.
main.h should include fruit.h not the other way around.
main.h should include stone.h not the other way around.
Also you should add include guards to your header files.
EDIT
Here's one way that works, (I can't believe I recommending code like this but still)
// map.h
#ifndef MAP_H
#define MAP_H
class Map {public: int size = 20};
extern Map map;
#endif
// fruit.h
#ifndef FRUIT_H
#define FRUIT_H
#include "map.h"
class Fruit { public: int pos = 1; draw() {return map.size;} };
extern Fruit fruit;
#endif
// stone.h
#ifndef STONE_H
#define STONE_H
#include "map.h"
#include "fruit.h"
class Stone { public: draw() {return map.size * fruit.pos;} };
extern Stone stone;
#endif
// main.cpp
#include "map.h"
#include "fruit.h"
#include "stone.h"
Map map;
Fruit fruit;
Stone stone;
This is not how you are supposed to write code.
Files (*.h or *.cpp) should only include files that they directly depend upon.
Files should not include files that they do not depend upon.
One way to break cyclical dependencies is to put the implementation in the foo.cpp source file instead of inline in the foo.h header file.
One way to break dependencies on global variables is to instead pass them in as parameters instead of having them hard-coded into the routines.
Use of a forward declaration can be used to avoid including an header file that is only used to declare the type. Only when the details of the type, such as its methods and footprint, are not important. Alas, forward declarations for template classes are trickier.
For the files in the OP example, here's an alternative implementation incorporating those suggestions.
fruit.h
#ifndef FRUIT_H
#define FRUIT_H
class Map;
class Fruit {
public:
int pos = 1;
auto draw(Map const&) -> int;
};
#endif
map.h
#ifndef MAP_H
#define MAP_H
class Map {
public:
int size = 20;
};
#endif
stone.h
#ifndef STONE_H
#define STONE_H
class Fruit;
class Map;
class Stone {
public:
auto draw(Map const& map, Fruit const& fruit) -> int;
};
#endif
fruit.cpp
// Identity.
#include "fruit.h"
// Other dependencies.
#include "map.h"
auto Fruit::draw(Map const& map) -> int {
return map.size;
}
stone.cpp
// Identity.
#include "stone.h"
// Other dependencies.
#include "fruit.h"
#include "map.h"
auto Stone::draw(Map const& map, Fruit const& fruit) -> int {
return map.size * fruit.pos;
}
main.cpp
#include <iostream>
#include "fruit.h"
#include "map.h"
#include "stone.h"
using std::cout;
int main() {
auto map = Map{};
auto fruit = Fruit{};
auto stone = Stone{};
map.size = 17;
fruit.pos = 3;
cout << "map.size is " << map.size << "\n";
cout << "fruit.pos is " << fruit.pos << "\n";
cout << "fruit.draw(map) is " << fruit.draw(map) << "\n";
cout << "stone.draw(map, fruit) is " << stone.draw(map, fruit) << "\n";
}
I'm trying to learn Inheritance mechanism in C++, I have made a Bancnote(Bills) class, and I want to make a class Card inheriting all the functions and variables from Class Bancnote.
And I get this type of error :
include\Card.h|6|error: expected class-name before '{' token|
BANCNOTE.H
#ifndef BANCNOTE_H
#define BANCNOTE_H
#include <iostream>
#include "Card.h"
using namespace std;
class Bancnote
{
public:
Bancnote();
Bancnote(string, int ,int ,int );
~Bancnote( );
int getsumacash( );
void setsumacash( int );
int getsumaplata( );
void setsumaplata( int );
int getrest( );
void setrest( int );
string getnume( );
void setnume( string );
void ToString();
protected:
private:
string nume;
int sumacash;
int rest;
static int sumaplata;
};
#endif // BANCNOTE_H
BANCNOTE.CPP
#include <iostream>
#include "Bancnote.h"
#include "Card.h"
using namespace std;
int Bancnote::sumaplata=0;
Bancnote::Bancnote(string _nume,int _sumacash,int _rest, int _sumaplata )
{
this->nume=_nume;
this->sumacash=_sumacash;
this->rest=_rest;
this->sumaplata=_sumaplata;
}
Bancnote::Bancnote()
{
this->nume="";
this->sumacash=0;
this->rest=0;
this->sumaplata=0;
}
Bancnote::~Bancnote()
{
cout<<"Obiectul"<<"->" <<this->nume<<"<-"<<"a fost sters cu succes";
}
string Bancnote::getnume()
{
return nume;
}
void Bancnote::setnume(string _nume)
{
this->nume=_nume;
}
int Bancnote::getsumacash()
{
return sumacash;
}
void Bancnote::setsumacash(int _sumacash)
{
this->sumacash=_sumacash;
}
int Bancnote::getsumaplata()
{
return sumaplata;
}
void Bancnote::setsumaplata(int _sumaplata)
{
this->sumaplata=_sumaplata;
}
int Bancnote::getrest()
{
return rest;
}
void Bancnote::setrest(int _rest)
{
this->rest=_rest;
}
void Bancnote::ToString()
{
cout<< "-----"<<getnume()<< "-----"<<endl;
cout<<"Suma Cash: "<<this->getsumacash()<<endl;
cout<<"Suma spre plata: "<<this->getsumaplata()<<endl;
cout<<"Restul:"<<this->getrest()<<endl;
}
CARD.H
#ifndef CARD_H
#define CARD_H
#include "Bancnote.h"
class Card: public Bancnote
{
public:
Card();
virtual ~Card();
protected:
private:
};
#endif // CARD_H
You have messed up the includes. What you have is more or less this:
Bancnote.h:
#ifndef BANCNOTE_H
#define BANCNOTE_H
#include "Card.h" // remove this
struct Bancnote {};
#endif
Card.h
#ifndef CARD_H
#define CARD_H
#include "Bancnote.h"
struct Card : Bancnote {}; // Bancnote is not yet declared
// when compiler reaches here
#endif
When in main you include Bancnote.h then this header includes Card.h so you try to declare Card before Bancnote is declared. Actually Bancnote does not need the definition of Card, so simply removing the include should fix it.
PS: there are other issues (see comments below your question). Most importantly it is not clear why a Card is a Bancnote. Second, never put a using namespace std; inside a header! (see here why)
main contains:
#include "num.h"
num * intObj = new num;
num.h contains:
#ifndef __EXPR_H__
#define __EXPR_H__
#include <string>
class num : public Expr {
//
};
#endif
expr.h contains:
#ifndef __EXPR_H__
#define __EXPR_H__
#include <string>
class Expr {
public:
virtual int eval() const = 0;
virtual std::string prettyPrint() const = 0;
virtual ~Expr();
};
#endif
Then I get:
error: ‘num’ was not declared in this scope
num * intObj = new num;
^
What can be the reason for this? I have also declared the class Expr in a different .h file, which is also included in main.
I get the same error with all the new classes I declared and am using.
You are using the same header guard __EXPR_H__ for both headers. Only one will be defined.
Change __EXPR_H__ in num.h to __NUM_H__ and it will be fine.
Try one of the following:
#include "expr.h" /* before num.h */
#include "num.h"
num * intObj = new num;
or
#ifndef __NUM_H__ /* Header file guard for num.h not expr.h here */
#define __NUM_H__
#include <string>
include "expr.h" /* #ifndef __EXPR_H and #define __EXPR_H__ in this .h file */
class num : public Expr {
//
};
#endif
#ifndef _ALLOCATOR_H
#define _ALLOCATOR_H
#include "ace/OS_NS_stdio.h"
#include "ace/OS_NS_string.h"
#include "ace/MMAP_Memory_Pool.h"
#include "ace/Malloc_T.h"
#include "ace/Null_Mutex.h"
#include "ace/PI_Malloc.h"
#include "ace/OS_NS_unistd.h"
#include "ace/Thread_Mutex.h"
#include "ace/Process_Mutex.h"
#include <string>
using namespace std;
class CAllocator
{
public:
CAllocator();
~CAllocator(void);
public:
bool Create(char* strPoolName);
void Destroy();
public:
char* NewMem(char* strBlockName,int nBlockSize);
char* FindMem(char* strBlockName);
bool FreeMem(char* strBlockName);
private:
typedef ACE_Malloc_T <ACE_MMAP_MEMORY_POOL,
ACE_Process_Mutex,
ACE_PI_Control_Block>
ALLOCATOR;
ALLOCATOR* m_pAllocator;
};
#endif //_ALLOCATOR_H
#ifndef _ARRAY_H
#define _ARRAY_H
#include "allocator.h"
template<typename T>
class CArray
{
public:
bool CreateArray(CAllocator* pAllocator,char* strArrayName,int nArraySize);
bool OpenArray(CAllocator* pAllocator,char* strArrayName);
public:
CArray()
{
m_pArrayData = NULL;
}
~CArray()
{
m_pArrayData = NULL;
}
public:
T* GetObject(int nIndex);
int GetArraySize();
private:
T* m_pArrayData;
};
#include "array.cpp"
#endif //_ARRAY_H
In the function CreateArray of the template class CArray,
the gcc compiler says CAllocator has not been declared.
but all the code worked under vs2010
please help,thanks gurus
Please stop naming like _ALLOCATOR_H. Name start with __ or _ followed by a capital letter is reserved for using by compiler and standard.
– Danh
change #ifndef _ALLOCATOR_H #define _ALLOCATOR_H to #ifndef ALLOCATOR_H #define ALLOCATOR_H Everything is ok! Thank u all – Jack
I really don't understand how to fix this redefinition error.
COMPILE+ERRORS
g++ main.cpp list.cpp line.cpp
In file included from list.cpp:5:0:
line.h:2:8: error: redefinition of âstruct Lineâ
line.h:2:8: error: previous definition of âstruct Lineâ
main.cpp
#include <iostream>
using namespace std;
#include "list.h"
int main() {
int no;
// List list;
cout << "List Processor\n==============" << endl;
cout << "Enter number of items : ";
cin >> no;
// list.set(no);
// list.display();
}
list.h
#include "line.h"
#define MAX_LINES 10
using namespace std;
struct List{
private:
struct Line line[MAX_LINES];
public:
void set(int no);
void display() const;
};
line.h
#define MAX_CHARS 10
struct Line {
private:
int num;
char numOfItem[MAX_CHARS + 1]; // the one is null byte
public:
bool set(int n, const char* str);
void display() const;
};
list.cpp
#include <iostream>
#include <cstring>
using namespace std;
#include "list.h"
#include "line.h"
void List::set(int no) {}
void List::display() const {}
line.cpp
#include <iostream>
#include <cstring>
using namespace std;
#include "line.h"
bool Line::set(int n, const char* str) {}
void Line::display() const {}
You need to put include guards in your headers.
#ifndef LIST_H_
#define LIST_H_
// List.h code
#endif
In list.cpp, you are including both "line.h" and "list.h". But "list.h" already includes "line.h" so "list.h" is actually included twice in your code. (the preprocessor is not smart enough to not include something it already has).
There are two solutions:
Do not include "list.h" directly in your list.cpp file, but it is a practice that does not scale: you have to remember what every of your header file includes and that will be too much very quickly.
use include guards, as explained by #juanchopanza
You are including "line.h" twice, and you don't have include guards in your header files.
If you add something like:
#ifndef LINE_H
#define LINE_H
... rest of header file goes here ...
#endif
to your header files, it will all work out fine.