I got error say [Error] extra qualification 'bezierCurve::' on member 'calCurve' [-fpermissive]. Could anyone explain to me why this happen? I've been looking for answer, but the I cannot solve the problem.
#ifndef _BEZIERCURVE_H_
#define _BEZIERCURVE_H_
#include "bezier.h"
class bezierCurve : public bezier{
private:
int numPoints;
float **controlPoints;
float **curvePoints;
void bezierCurve::calCurve(); //and error here
public:
bezierCurve(int numPoints, float *points[3]);
void bezierCurve::setShowPoints(bool showControlPoints); // I got the error here
virtual void draw();
~bezierCurve();
};
#endif
This is an error because it is not valid C++ syntax. The elephant in the room is that VisualC++ has historically not considered this an error. But GCC has since around version 4.
Simply removing the extra qualifications fixes the code.
For example:
#ifndef __ANIMAL_H__
#define __ANIMAL_H__
class Animal
{
...
int Animal::getLegCount();
bool Animal::hasFur();
};
#endif
Is not correct, member must be defined without the Classname:: prefix:
#ifndef __ANIMAL_H__
#define __ANIMAL_H__
class Animal
{
...
int getLegCount();
bool hasFur();
};
#endif
You are confusing declarations and definitions. When you declare a member function, it's in the context of the class already so classname:: is redundant. When you define the body of a function outside of the class, you need the classname:: so that the compiler knows which class it belongs to.
class bezierCurve : public bezier{
void setShowPoints(bool showControlPoints);
};
void bezierCurve::setShowPoints(bool showControlPoints) {
}
this is what output i get. suppose it's not like this.
#kingsley, this shown the output when i'm running the codes after I remove _s from sscanf_s().
Related
I have a class called scratch and have used scratch.h to declare it.
Now I have another class called scratch2 under scratch2.h and want to create an object of scratch as a shared pointer.
This is the syntax I used inside scratch2 class declartion:
std::shared_ptr<scratch> newObject(new scratch());
But I am getting this error: Error: Expected type specifier
So I tried this instead:
std::shared_ptr<scratch> newObject2 = std::make_shared<scratch>();
which works fine. Can anyone please tell me why the first one isn't working?
My scratch.h code:
#ifndef _SCRATCH_
#define _SCRATCH_
#include <iostream>
class scratch {
private:
int _a;
float _b;
std::string _s;
public:
scratch();
scratch(int a, float b, std::string n);
~scratch();
};
#endif
and my scratch2.h:
#ifndef _SCRATCH_2_
#define _SCRATCH_2_
#include "scratch.h"
#include <memory>
class scratch2 {
std::shared_ptr<scratch> newObject(new scratch()); // Expected a type specifier error occurs here
std::shared_ptr<scratch> newObject2 = std::make_shared<scratch>(); // works fine here
};
#endif
Because in the context of declaring class members:
std::shared_ptr<scratch> newObject(new scratch());
This initially looks to the compiler as a class method declaration. C++'s syntax is very complicated. You can look at the entire declaration and understand what it's trying to do, but the compiler is parsing keywords one keyword at a time, and sees this:
type name( ...
inside a class declaration, and this starts to look like a class method declaration, and that's what the compiler tried to parse, and failed.
The formal specification of the C++ language spills a lot of ink on the subject of how things should be declared, mindful of the current state of compiler technology.
You need to work with the compiler, and use an alternate syntax that's unambiguous:
std::shared_ptr<scratch> newObject = std::shared_ptr<scratch>(new scratch());
Verified with gcc 5.3
Inside of a class definition, there are only two ways you're allowed to initialize your members. You can use = and you can use {}. You are not allowed to use ():
struct foo {
int x = 4; // OK
int y{7}; // OK
int z(12); // error
};
Admittedly, the compiler error in this case is extremely unhelpful.
First: My English is not that good yours is. Excuse me.
I'm using Ubuntu (I don't know if this is important) and I had issues with Code::Blocks since I started to use it. But I fixed them by re-opening the program. But now, I get a really crazy error when compiling the code. I included a file just like usual:
#include "GameObjectUtility.h"
and I used the class "GameObjectUtility" to declare a member object, just like this:
class GameObject
{
std::vector<GameObjectUtility> uts;
// Error here:
// GameObjectUtility was not declared in this scope
}
So, is this my fault or is there something buggy with Code::Blocks?
And, additionally, is there a way of saying to the Linker: First execute this file and then the other?
Thank you for your answers!
EDIT: .h and .ccp file GameObjectUtility:
So this is GameObjectUtility.h:
#ifndef GAMEOBJECTUTILITY_H
#define GAMEOBJECTUTILITY_H
#include <string>
#include "Collision.h"
class GameObjectUtility
{
public:
GameObjectUtility();
virtual ~GameObjectUtility();
virtual void Update() = 0;
virtual void LateUpdate() = 0;
virtual void FixedUpdate() = 0;
static void SendMsg(std::string msg);
protected:
private:
virtual void GetMsg(std::string msg) = 0;
};
#endif // GAMEOBJECTUTILITY_H
And in GameObjectUtility.cpp are just two empty definitions of constructor and destructor
Since class GameObjectUtility is pure virtual, you cannot instantiate it.
You can only store std::vector<GameObjectUtility*> in class GameObject.
I can't get method overriding to work. Right now I have a class called Sprite, and two subclasses; Let's call them Goomba and Koopa. Instances of Koopas and Goombas are stored in an std::list of sprites called spriteList, and an iterator goes through this list and calls each sprite's behave() function.
I can get this to work with Goombas alone, by defining the behavior function as Sprite::behave(). But if I try to do the same thing with Koopas, the compiler gets mad because Sprite::behave() is already defined in Goomba. What am I doing wrong? I get the feeling that the answer is an extremely simple syntax issue, but looking online yielded no examples that looked quite like my code.
I'll paste some code, hopefully it'll help. This isn't my exact source code, so I apologize for any typos.
//Sprite.h:
#ifndef SPRITE_H
#define SPRITE_H
class Sprite {
private:
float xPosition; float yPosition;
public:
Sprite(float xp, float yp);
void move(float x, float y); //this one is defined in Sprite.cpp
void behave(); //this one is NOT defined in Sprite.cpp
};
#endif
//Goomba.h:
#ifndef GOOMBA_H
#define GOOMBA_H
#include "Sprite.h"
class Goomba : public Sprite {
public:
Goomba(float xp, float yp);
void behave();
};
#endif
//Goomba.cpp:
#include "Goomba.h"
Goomba::Goomba(float xp, float yp): Enemy(xp, yp) {}
void Sprite::behave(){
Sprite::move(1, 0);
}
//Koopa.h looks just like Goomba.h
//Koopa.cpp
#include "Koopa.h"
Koopa::Koopa(float xp, float yp): Enemy(xp, yp) {}
void Sprite::behave(){
Sprite::move(-2, 1);
}
In Sprite you have to declare the function as virtual
virtual void behave();
Then in Goomba you should state that you are going to override that function
virtual void behave() override;
Note: The override keyword is new as of C++11
In both Koopa.cpp and Goomba.cpp you are defining Sprite::behave. This results in two definitions, as your toolchain told you. You want to define Koopa::behave and Goomba::behave, respectively, in those files.
You also want to define Sprite::behave in Sprite.cpp (you said you currently do not define it anywhere).
You will also want to make Sprite::behave a virtual function in order to get the polymorphic behavior you are after working the way you likely expect it to:
class Sprite {
// ...
// You can either define Sprite::behave in Sprite.cpp or change the declaration to:
// virtual void behave() = 0;
// to make it "pure virtual," indicating that subclasses must provide an implementation.
virtual void behave();
};
In Goomba.cpp, for example:
#include "Goomba.h"
Goomba::Goomba(float xp, float yp): Enemy(xp, yp) {}
void Goomba::behave(){
...
}
Had some issues in my code recently surrounding what I now know of as a Circular dependency. In short there are two classes, Player and Ball, which both need to use information from the other. Both at some point in the code will be passed a reference of the other (from another class that will include both .h files).
After reading up on it, I removed the #include.h files from each one and went with forward declaration. This solved the issue of being able to declare the classes in eachother, but I'm now left with an "Incomplete type error" when trying to access a passed reference to the object. There seem to be a few similar examples around, though often mixed with more complex code and hard to narrow down to the basics.
I've rewritten the code in it's simplest form (a skeleton essentially).
Ball.h:
class Player;
class Ball {
public:
Player& PlayerB;
float ballPosX = 800;
private:
};
Player.h:
class Ball;
class Player {
public:
void doSomething(Ball& ball);
private:
};
Player.cpp:
#include "Player.h"
void Player::doSomething(Ball& ball) {
ball.ballPosX += 10; // incomplete type error occurs here.
}
Any help understanding why this is the case would be greatly appreciated :)
If you will place your definitions in this order then the code will be compiled
class Ball;
class Player {
public:
void doSomething(Ball& ball);
private:
};
class Ball {
public:
Player& PlayerB;
float ballPosX = 800;
private:
};
void Player::doSomething(Ball& ball) {
ball.ballPosX += 10; // incomplete type error occurs here.
}
int main()
{
}
The definition of function doSomething requires the complete definition of class Ball because it access its data member.
In your code example module Player.cpp has no access to the definition of class Ball so the compiler issues an error.
Player.cpp require the definition of Ball class. So simply add #include "Ball.h"
Player.cpp:
#include "Player.h"
#include "Ball.h"
void Player::doSomething(Ball& ball) {
ball.ballPosX += 10; // incomplete type error occurs here.
}
Here is what I had and what caused my "incomplete type error":
#include "X.h" // another already declared class
class Big {...} // full declaration of class A
class Small : Big {
Small() {}
Small(X); // line 6
}
//.... all other stuff
What I did in the file "Big.cpp", where I declared the A2's constructor with X as a parameter is..
Big.cpp
Small::Big(X my_x) { // line 9 <--- LOOK at this !
}
I wrote "Small::Big" instead of "Small::Small", what a dumb mistake..
I received the error "incomplete type is now allowed" for the class X all the time (in lines 6 and 9), which made a total confusion..
Anyways, that is where a mistake can happen, and the main reason is that I was tired when I wrote it and I needed 2 hours of exploring and rewriting the code to reveal it.
In my case it was because a typo.
I had something like
struct SomethingStrcut { /* stuff */ };
typedef struct SomethingStruct smth;
Notice how the name of the structure is not the same one as the type definition.
I misspelled struct to strcut.
Look into your code and see wether you have some typos.
I need to call properties and functions of an object from a different class.
The idea is passing 'this' as a parameter to the other class constructor. E.g.:
instance = ClassName(this);
And then do:
ParentClass parentInstance;
ClassName::ClassName(MainApp _instance){
parentInstance = _instance;
}
However, my compiler says that ParentClass does not name a type. Ideas?
Also, should I use a pointer to save memory? How?
Thanks in advance.
UPDATE:
Ok, sorry for the delay. Here it goes the actual code. First, a simple class.
Game class:
Header file
#ifndef _GAME
#define _GAME
#include "ofMain.h"
class Game{
public:
Game();
~Game();
void hi();
};
#endif
cpp file:
#include "Game.h"
Game::Game(){}
Game::~Game(){}
void Game::hi(){
cout << "hi, I'm game! " << endl;
}
Then, from MainApp I create the object:
- Relevant code on header file:
#ifndef _MAIN_APP
#define _MAIN_APP
#include "ofMain.h"
#include "Game.h"
class MainApp : public ofSimpleApp{
public:
Game game;
};
#endif
Relevant code on the cpp file:
game = Game();
game.hi();
This obviously works as I'm only creating a bloody object. However, problem comes with composition.
I could pass the main app as argument in the constructor, I could pass it via game.setParent(this);... problem is, I can't even define the variable to store the reference to the app.
E.g.: (making it easy/inefficient without pointers or anything)
Game.h:
#define _GAME
#ifndef _GAME
#include "ofMain.h"
#include "MainApp.h"
class Game{
MainApp app;
public:
Game();
~Game();
void hi();
};
#endif
This returns a "does not name a type" error and declaring class MainApp returns an "incomplete type" error
I'm sure I'm doing something dumb.
UPDATE 2:
The problem with that method is that I can't call a function of the pointed object now.
This is Game.h:
#ifndef _GAME
#define _GAME
#include "ofMain.h"
class MainApp;
class Game{
public:
Game();
Game(MainApp* _app);
~Game();
void hi();
MainApp* app;
};
#endif
As you see, app (of the type MainApp) is passed as a parameter. That's fine, MainApp exists as it's the forward declaration. However, when I try to call any of app's functions I can't (compiler error saying Request for member appHi in .... which is non-class type 'MainApp'.
MainApp is NOT included in Game.h but Game.h IS included in MainApp.h.
Ideas?
The problem is you have a circular reference - Game includes MainApp, and MainApp includes game. You need a 'forward declaration', as per the example by DeadMG.
See here.
It's called composition and is a common pattern. It's highly efficient in both semantics and in terms of runtime speed/memory footprint.
Your code example is a little too much pseudocode for me to read it correctly. Let me show you how it's done.
class X;
class Y {
...
void DoSomething(X* x, ... args);
};
class X {
Y y;
void DoSomething() {
y.DoSomething(this, args);
}
};
I think there may be two issues here:
1) You need to declare the ParentClass (i.g. #include its .hpp-file) before using it
2) The assignment "parentInstance = _instance" will invoke the assignment operator, which i'm guessing is not what you want. let "parentInstance" be a pointer instead.
Note the section on "#include."
http://www.cplusplus.com/doc/tutorial/program_structure/
After the "Intro to the C++ Language" section look for the verbiage about #include.
http://www.cprogramming.com/tutorial/lesson1.html
Namespaces:
http://www.tenouk.com/Module23.html
HTH
That's not how things work in C++. Unlike javascript, you cannot inject methods or fields into existing objects at runtime.
Madsen is on the right track here, but we need more code; What is the class heirarchy of ParentClass, ClassName and SaleraApp. Which classes are base and/or dervied?
When you write: parentInstance = _instance; the compiler will try to generate a default copy constructor if one is not defined. Your problem might be that you are trying to create a dervied class object from a base class pointer.
Also, "this" is a pointer.
If all you need to do is use functions and data members of another class, read up on the friend keyword. It will allow access to class members from other classes.
UPDATE: Alternatively, store a pointer or reference to the object you need access to, and make getters for data members and make the functions public... but I get the feeling this is not what you're after...