I am working in restructuring a former program which relies heavily on a external library
ChronoEngine.lib
I created a new project which holds the same additional include directories, linkers etc... than the former one
I have the following piece of code in a header file
#ifndef DRAW
#define DRAW
#include "physics/CHsystem.h"
class draw
{
public:
// Change size
static void changeSize(int w, int h);
// World definition
static void drawSky(double halfSize, double red, double green, double blue);
static void drawChair() ;
static void drawCDG() ;
static void drawPlane();
// Geometrical definition
static void drawSphere(ChBody* body);
static void drawBox(ChBody* body);
};
#endif
this is the same header file as in the previous project, but here visual studio does not find the definition of ChBody (which is included in the "physics/CHsystem.h" header file definition - this file includes physics/ChBody.h -)
when i right click on ChBody to find the reference, visual studio finds 5 references (1 is the real definition (from ChBody.h), 4 others are forward references in others files from the library)
how can I tell my program to find the real definition of the class ? Apparently, it is not a problem of being linked to the library, but more like a referencing problem
my main.cpp is only printing something to the screen for the time being, and draw.cpp is empty (i haven't defined the function i am declaring in draw.h for the time being)
Thanks
Best
Vincent
Thanks a lot
Actually that was a fairly easy problem to solve
The problem was coming from the fact that the other classes (such as ChBody) were defined in a namespace
therefore, adding
using namespace <the name of the namespace>;
before the definition of the class and after the #include solves this kind of issues.
Thanks
Best
Vincent
Related
This is my first time encountering this type of linking error for 20 years while trying to use other people's code.
Here I will be brief and using abbreviated examples.
Say the file enums.hpp
==== content====
#ifndef _BLABLA_
#define _BLABLA_
enum SomeKind { BLACK, RED, GREEN }
static void parse(const std::string& s, SomeKind) {
// definition
}
..... More enum, and static functions
#endif
In this file there are several enum and parse. Because of the STATIC keyword, the compiler will complain about the unused functions. I experimented by moving the definition of those function to a enum.cpp file. Then at link time, I am getting the error message:
undefined reference to `someNameSpace::SomeKind
One solution I will try to use the library as is (I will probably do that). This project (I am using) is a CMake project. What's a better way of organizing the original code to git rid of both problems: unused function, and undefined reference?
After removing the static label then it get rid of the linking problem of the enum. Essentially the new organization is as:
enums.hpp
enum SomeKind { }
void someFunction(SomeKind sk);
enums.cpp
void someFunction(SomeKind sk) {
// definition here
}
I think elimination of the static make the function visible and some how included in the linking stage. This is a big library, I have only a few hours looking into this library.
I have been recently practicing managing multiple objects and drawing them in C++ using SFML library. I wanted my textures and future resources to be more reusable so I decided to make use of Thor library which suits my needs really well.
So I've written first few lines of code based on what you can find in this tutorial and the compiler always says:
main.cpp|12|error: 'textures_holder' does not name a type
This line gives an error :
textures_holder.acquire("Dirt", thor::Resources::fromFile<sf::Texture>("Textures\\dirt_block.png"));
I'm using Code::Blocks IDE with MinGW compiler and SFML 2.5.0.
Here's my main.cpp and the header file which contains extern object :
//...
#include <Thor/Resources.hpp>
#include "Dirt_Block.h"
using namespace std;
//Adding textures to the texture library
//THIS LINE GIVES AN ERROR
textures_holder.acquire("Dirt", thor::Resources::fromFile<sf::Texture>("Textures\\dirt_block.png"));
//Rest of code...
Dirt_Block.h (only the upper part) :
#ifndef DIRT_BLOCK_H
#define DIRT_BLOCK_H
#include <SFML\Graphics.hpp>
#include <vector>
#include <Thor/Resources.hpp>
#include <Thor/Resources/SfmlLoaders.hpp>
extern sf::Vector2u screenRes;
extern thor::ResourceHolder<sf::Texture, std::string> textures_holder;
//Rest of the code
I'd like to know what is causing this error and maybe help others who may experience similiar frustrating problems. Thanks for help.
EDIT :
As suggested in the comment I've declared a few extern int variables in the Dirt_Block.h so now it looks like this :
//...
extern int test_int_up;
extern sf::Vector2u screenRes;
extern thor::ResourceHolder<sf::Texture, std::string> textures_holder;
extern int test_int_d;
//...
And then assinged to them some value in main.cpp :
//...
test_int_up = 55;
test_int_d = 55;
//Adding textures to the texture library
textures_holder.acquire("Dirt", thor::Resources::fromFile<sf::Texture>("Textures\\dirt_block.png"));
//...
But the compiler gives error :
main.cpp|9|error: 'test_int_up' does not name a type
main.cpp|10|error: 'test_int_d' does not name a type
main.cpp|12|error: 'textures_holder' does not name a type
Much less distracting to see what your problem is without all the extraneous code!
C++ programs don't start from the top of the file and run code down to the bottom. They start at the main(), and control flow proceeds from there, with one thing triggering another.
(Note: That doesn't take into account global constructor ordering, which does go in order of declaration--but you have no guarantee of the order declarations from "different files" might run in.)
Point being, you can't just make random function or method calls in the middle of a file. That's where you put declarations. You have to be inside of a function or method to make calls, e.g.
int main() {
textures_holder.acquire(
"Dirt",
thor::Resources::fromFile<sf::Texture>("Textures\\dirt_block.png")
);
...
}
This question already has answers here:
Why have header files and .cpp files? [closed]
(9 answers)
Closed 5 years ago.
Someone asked a question similar to mine here:
Function declaration inside or outside the class?
Why do you just declare a function inside a .h file but not the definition, and then write the whole definition in a .cpp file later? What's the point? Why don't you just put the whole function inside a class inside the header file instead of just declaring it? It seems repetetive and pointless.
How do I structure a program to use the header files and other .cpp files without piling functions, classes, and variables into the main file? Could I get an example of a simple program using a .h file and maybe a couple of .cpp files?
Why do you just declare a function inside a .h file but not the definition, then write the whole definition in a .cpp file later? What's the point? Why don't you just put the whole function inside a class inside the header file instead of just declaring it? It seems repetetive and pointless.
When you modify a header, all code that references the contents of that header via #include must be re-compiled.
If you have a header that is included by many other files, then a single change to the contents of that header may require a rather lengthy rebuild of your entire project. This may not seem important if you are only working on small projects, but imagine production applications with thousands of classes.
Another benefit is when writing a library. When you provide your library binaries for others to use, you need only provide the headers. In this way you can have proprietary source code within the source files themselves that the users do not have access to.
Finally, by separating content into separate header and source files, it makes learning a library easier. Many times when working with a new API I just want to skim the header to get a gist of the class and it's functions. I do not need to see, or want to parse through, the implementation.
This is not to say that you have to have separate header and source files. There are many header-only libraries out there (such as GLM) that serve a wide audience. Of course, these are typically distributed as header-only so that no binary (static or dynamic) is needed.
And of course, if you are creating a template class the implementation generally goes within the header.
How do I structure a program to use the header files and other .cpp files without piling functions, classes, and variables into the main file? Could I get an example of a simple program using a .h and a couple of .cpp files.
This is perhaps beyond the scope of this site, but here is a simple example.
Rectangle.hpp
#ifndef H__RECTANGLE__H
#define H__RECTANGLE__H
class Rectangle
{
public:
Rectangle(float width = 0.0f, float height = 0.0f);
~Rectangle();
void setWidth(float width) noexcept;
void setHeight(float height) noexcept;
float getArea() const noexcept;
protected:
private:
float m_fWidth;
float m_fHeight;
};
#endif
Rectangle.cpp
#include "Rectangle.hpp"
Rectangle::Rectangle(float const width, float const height)
: m_fWidth{ width },
m_fHeight{ height }
{
}
Rectangle::~Rectangle()
{
}
float Rectangle::getArea() const noexcept
{
return m_fWidth * m_fHeight;
}
void Rectangle::setWidth(float const width) noexcept
{
m_fWidth = width;
}
void Rectangle::setHeight(float const height) noexcept
{
m_fHeight = height;
}
main.cpp
#include "Rectangle.hpp"
#include <iostream>
int main()
{
Rectangle rectA{ 5, 5 };
Rectangle rectB{ 3, 2 };
std::cout << "Area of Rectangle A is: " << rectA.getArea() << std::endl;
std::cout << "Area of Rectangle B is: " << rectB.getArea() << std::endl;
return 0;
}
Now how to compile and link these files together depends on the IDE you use.
I'm a novice programmer, still in the midst of trying to learn C++ and OOP design basics. The project that I've been working on to teach myself is a C++ game that has multiple classes, files, states, etc. However, I keep running into snags with file organization that range from simply struggling with where to create objects to compile-breaking linker errors.
Here's an example of some of the errors that I've been getting:
1>SMGA.obj : error LNK2005: "class Engine smgaEngine" (?smgaEngine##3VEngine##A) already defined in Engine.obj
1>SplashScreenState.obj : error LNK2005: "class Engine smgaEngine" (?smgaEngine##3VEngine##A) already defined in Engine.obj
1>StateManager.obj : error LNK2005: "class StateManager gameStateManager" (?gameStateManager##3VStateManager##A) already defined in Engine.obj
1>MSVCRTD.lib(cinitexe.obj) : warning LNK4098: defaultlib 'msvcrt.lib' conflicts with use of other libs; use /NODEFAULTLIB:library
I've looked around online and I've seen a lot of ~similar~ problems that involve bad include guards or the inclusion of .cpp files instead of .h files. But I haven't done that in my code, so I'm at a loss.
Now, I'm guessing that the error is telling me that I'm trying to create the smgaEngine object of the Engine class (and the gameStateManager object of the StateManager class) twice, but I'm not sure why...
The thing that stands out about these two objects (smgaEngine and gameStateManager) is that I declared them in their corresponding class' .h files immediately after the class declaration. Could this be the issue? - They're still within the include guards, and I wasn't too sure about where else to put them in my code... Would this sloppy coding be the cause of linker errors?
Here's one of the suspect classes...
#ifndef ENGINE_H
#define ENGINE_H
#include <SDL.h>
#include "Timer.h"
class Engine
{
private:
static const int screenWidth = 480;
static const int screenHeight = 270;
static const int screenBPP = 24;
bool running;
SDL_Surface *mainScreen;
SDL_Event eventHolder;
Timer fpsTimer;
public:
Engine();
~Engine();
void init();
void handleEvents();
void handleLogic();
void handleRender();
void cleanUp();
SDL_Event *getEvent();
SDL_Surface *getMainScreen();
bool isRunning();
void setRunning(bool tempRunning);
} smgaEngine;
#endif
And here's the other one:
#ifndef STATEMANAGER_H
#define STATEMANAGER_H
#include "SplashScreenState.h"
#include <vector>
class GameState;
class StateManager
{
private:
std::vector<GameState*> stateStack;
SplashScreenState *splashState;
public:
StateManager();
~StateManager();
void init();
void changeState( GameState *tempNextState );
void addState( GameState *tempNextState );
void removeState();
//returns the back() element of the stateStack vector..
GameState* getTopState();
void handleEvents();
void handleLogic();
void handleRender();
} gameStateManager;
#endif
I've been trying my best to learn C++ and OOP, but I've really been struggling. It seems that every time I attempt to make clean code with encapsulated classes, I end up with a confusing mess. I'm trying to prevent a high degree of class coupling, but I often end up with either linker errors or a lack of ability to communicate between classes... Is it creation of class instance objects within the header files that is causing these errors or is it something else? And if that is the cause of my linker errors, then where should I be creating these objects?
You have defined two global variables, smgaEngine and gameStateManager in your header files, and you have included those header files in two (or more) source files. So you get multiple definition errors. Include guards don't stop header files being included twice in different source files (how could they?) they stop header files being included twice in the same source file.
You're quite close to the correct answer (at least you have a good understanding of the problem). The right way is this
// header file Engine.h
class Engine
{
};
extern Engine smgaEngine;
// in one source file (say Engine.cpp)
Engine smgaEngine;
What you have now is a declaration in the header file (extern makes it a declaration), but a definition in the source file. You can have as many declarations as you like (as long as they are consistent) but you must have only one definition. So for global variables put declarations in the header file and put a definition in one of the source files.
I've written a small program that utilizes the Fast Light Toolkit and for some reason a compiler error is generated when trying to access the functions in the cmath header.
Such as error ::acos has not been declared.
This goes on for pretty much every function it tries to use in the header. What could I be missing?
The header files I have included are
Simple_window.h
Graph.h
both of which are part of the FLTK.
The code is this:
#include "Simple_window.h" // get access to our windows library
#include "Graph.h" // get access to graphics library facilities
int main()
{
using namespace Graph_lib; // our graphics facilities are in Graph_lib
Point tl(100,100); // to become top left corner of window
Simple_window win(tl,600,400,"Canvas"); // make a simple window
Polygon poly; // make a shape (a polygon)
poly.add(Point(300,200)); // add a point
poly.add(Point(350,100)); // add another point
poly.add(Point(400,200)); // add a third point
poly.set_color(Color::red); // adjust properties of poly
win.attach(poly); // connect poly to the window
win.wait_for_button(); // give control to display engine
}
Edit: Here is example code of when the compiler error is generated. This is inside the cmath header.
namespace std
{
// Forward declaration of a helper function. This really should be
// an `exported' forward declaration.
template<typename _Tp> _Tp __cmath_power(_Tp, unsigned int);
inline double
abs(double __x)
{ return __builtin_fabs(__x); }
inline float
abs(float __x)
{ return __builtin_fabsf(__x); }
inline long double
abs(long double __x)
{ return __builtin_fabsl(__x); }
using ::acos; //ERROR HERE
inline float
acos(float __x)
{ return __builtin_acosf(__x); }
inline long double
acos(long double __x)
{ return __builtin_acosl(__x); }
template<typename _Tp>
inline typename __enable_if<double, __is_integer<_Tp>::_M_type>::_M_type
acos(_Tp __x)
{
return __builtin_acos(__x);
}
Edit: Code::blocks is saving files as C files....
When you include the C++ version (<cXXXX>) of standard C libraries all the symbols are defined within the std namespace. In C++ you do not need to link against the math library (-lm is not required)
#include <cmath>
#include <iostream>
int main()
{
std::cout << std::fabs( -10.5 ) << std::endl;
}
I had this problem - it was driving me crazy but I tracked down the cause, and it was a little different than what I've seen reported on this issue.
In this case, the general cmath header (or math.h - the error and solution occur in C++ or C) had architectural environment switches to include architecture specific math subheaders. The architecture switch (environment variable) hadn't been defined, so it was punting and not actually including the headers that truly defined the math functions.
So there was indeed a single math.h or cmath.h, and it was included, but that wasn't enough to get the math functions. In my case, rather than define the architectural variable, I instead found the location of the correct sub math headers and added them to my compile path. Then the project worked!
This seems to be an issue that comes up a lot when porting Linux projects to OS-X. I'd imagine it might occur anytime a project was moved betwee platforms such that the standard library headers are arranged differently.
Jeff
Since your code as shown above does not directly call acos(), there is arguably a bug in one of the headers that you do use. It appears there is some (inline) code in one of the headers that invokes the acos() function without ensuring that the function is properly declared. This might be a macro or an inline function.
The best fix is to ensure that the headers are self-contained - change the headers.
If that is not possible, the hackaround is to include the appropriate header (#include <cmath>, probably) in the source code.
The program is able to access the cmath header, the error is in the cmath header itself.
In that case, you will probably need to provide a global acos() function (declaration at least, possibly definition too) that calls onto std::acos():
double acos(double x) { return std::acos(x); }
Just make sure this is not inside any namespace - not even the anonymous one. (Check compiled with G++ 4.0.1 on MacOS X, with '#include <cmath>' preceding it. Given that you have a problematic <cmath> header, you might need to get fancy:
extern double std::acos(double);
double acos(double x) { return std::acos(x); }
#include <cmath>
This is pretty nasty - are you sure there isn't a bug-fixed version of your compiler?
Is there any chance that you've got '#include <cmath>' inside a namespace?
It also happens in Visual C++, in programs that do not sapuse to use cmath.
I found that the problem is that I used main.c file instead of main.cpp file.
The error is most likely to be in your code and not in cmath... unless you changed something in cmath. Could you copy the errors and tell us what is the application you are using to program?