so i'm having a problem: I cutted out some coding(structs) and pasted it in a new Header-file. I included the new Header-file everywhere it is needed, so it shouldnt get me an error, but after i tried building my dll file, i got tons of errors saying that those structs i cutted out/pasted are redefinitions. I clicked on some of those "redefinitions" and the "originals" and i got to the same struct the same time, meaning there is only one of them so it cant be a redefinition. I'm so confused at the moment and i would really appreciate some help! Thanks in advance :)
EDIT:
i moved this:
struct Game_s
{
bool loaded;
bool FirstUser;
bool AlwaysVerfied;
bool DoingUnlockAll;
int Globaltimer;
int MaxUnlockAll;
time_t t;
};
Game_s Game;
from a Header file called MW2Class.h to another class called Structs.h, looking like this:
#include "stdafx.h"
#include <stdio.h>
#include <string>
#include <xbox.h>
struct Game_s
{
bool loaded;
bool FirstUser;
bool AlwaysVerfied;
bool DoingUnlockAll;
int Globaltimer;
int MaxUnlockAll;
time_t t;
};
Game_s Game;
Your issue is you have a global variable declared in your header file
Game_s Game;
Is going to add Game to every translation unit you include the header in(include guards do not stop this). When you get to the linking stage the linker will see all of theses global variables that are the same and will not know what to do with them.
If you really want the global variable you will need to declare it with extern and define it in one translation unit. For more information on that see: Global variables in header file
Make sure to add the inclusion guard to your headers :
Suppose your header is test_file.hpp, the include guards will be :
#ifndef TESTFILE_HPP_
#define TESTFILE_HPP_
#endif
That prevents multiple inclusions of your header.
Edit :
1 - in your case
#ifndef STRUCTS_H_
#define STRUCTS_H_
#endif
Related
I want to run a small simulation in c++.
To keep everything nice and readable I seperate each thing (like all the sdl stuff, all the main sim stuff, ...) into it's own .h file.
I have some variables that I want all files to know, but when I #include them in more then one file other the g++ compliler sees it as a redefinition.
I understand why he does this, but this still leaves me with my wish to have one file where all important variables and constants for each run are defined and known to all other files, to easily find and change them when running my simulation.
So my Question here: Is there a good workaround to achieve that or something similar?
You can put the declarations for all the globals in a header and then define them in a source file and then you will be able to use those global variables in any other source file by just including the header as shown below:
header.h
#ifndef MYHEADER_H
#define MYHEADER_H
//declaration for all the global variables
extern int i;
extern double p;
#endif
source.cpp
#include "header.h"
//definitions for all the globals declared inside header.h
int i = 0;
double p = 34;
main.cpp
#include <iostream>
#include "header.h" //include the header to use globals
int main()
{
std::cout << i <<std::endl;//prints 0
std::cout<< p << std::endl;//prints 34
return 0;
}
Working demo
Mark them as extern in the header and have one translation unit that defines them.
Note: Without LTO (link time optimization) this will seriously slow down your simulation.
Note: The question has already been answered here undirectly
The problem is not include guards : they won't help across different
translation units
Note: I know the solution is to use extern keyword.
I'm new to C++. I have a problem understanding #ifndef in header files. When I do something like this, I get an error saying that the variables game_over and turn are already defined.
/*chess.h*/
#ifndef CHESS
#define CHESS
#include <iostream>
#include "chessboard.h"
using namespace std;
bool game_over;
char turn;
chessboard board;
int main();
#endif
/*bishop.cpp*/
#include "bishop.h"
#include "chess.h"
bishop::bishop(string pos, char color)
{
int x = pos[0] - 97;
int y = pos[1] - 1;
name = "bishop";
this->color = color;
board.add_new(*this);
}
/*chess.cpp*/
#include "chess.h"
int main()
{
...
}
Why are the variables defined twice in here? I thought that first time when chess.h is included, CHESS is defined. So in bishop.cpp, #include "chess.h" will not do anything since the header will skip to #endif from #ifndef CHESS. But it does not work like that obviously. Why am I wrong?
The #ifndef only blocks the code if the symbol is defined within the same translation unit, at a point before the #ifndef. A translation unit is a source file (.cpp) and all the files that are included into it. Since you're compiling two source files, they'll both have a complete include of the .h file.
You already appear to know how to handle the problem of defining global variables in a header file: declare them extern in the header, and put a definition into one of the sources. I would be remiss though if I didn't warn you to avoid globals in the first place, as your programs grow they'll make your life difficult.
I am getting stuck using this class, when I used in the main.cpp there is no problem and execute perfectly, but when I use it as a member class the compiler doesn't like it and sends the message "Multiple definition of:"
Here is the class:
RTPSocket.h:
#ifndef RTP_SOCKET_HDR
#define RTP_SOCKET_HDR
namespace RTPConnection
{
enum EMode
{
Sender,
Receiver
};
template<EMode Mode>
class RTPSocket
{
};
}//end namespace
#define RTP_SOCKET_IMP
#include "RTPSocket_Imp.h"//file where i declare the implementation code
#undef RTP_SOCKET_IMP
#endif
this class by itself doesn't have any problem but when i use it in my class, but ....
used in another class
my file.h
#include RTPSocket.h
class CommClass
{
private:
RTPSocket<RTPConnection::Receiver> * mRTPServer;
}
the compiler give this error message:
multiple definition of 'enum RTPConnection::EMode'
this is a method that is declared in another file "rtpsocket_imp.h"
with the guard declared:
template<EMode Mode>
void RTPSocket<Mode>::write(char* aArray,
const size_t aiSize)
{
std::string message("The write function is operative only on Sender Mode");
throw BadTemplate(message);
}
You want include guards around the header:
#ifndef RTPSOCKET_H
#define RTPSOCKET_H
// header contents go here
#endif
This will prevent the header contents from being included more than once per source file, so you will not accidentally get multiple definitions.
UPDATE: Since you say you have include guards, then possible causes of the error might be:
misspelling the include guard name, so it doesn't work
defining something with the same name in another header (or the source file that includes it)
undefining the include guard name.
But without seeing code that reproduces the error, I can only guess what might be wrong.
You need an include guard.
Inside the RTPSocket.h file at the top put
#ifndef RTPSOCKET_INCLUDED
#define RTPSOCKET_INCLUDED
and at the end put
#endif
If that's not the problem, and you do have an include guard, I suggest you search for
enum EMode
in your code and find all the places you have defined it, and make sure you just define it once.
My problem was the CMakeLists.txt that was building this project.
My fault!
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Why does this not prevent multiple function declarations?
Global.h
#ifndef Global_h
#define Global_h
#include <iostream>
unsigned char exitStatus;
#endif
OutputHandler.h
#ifndef OutputHandler_h
#define OutputHandler_h
#include "Global.h"
class OutputHandler {
private:
static bool instanceExists;
// more code
#endif
Root.h
#ifndef Root_h
#define Root_h
// declarations
OutputHandler *output;
#endif
Root.cpp
#include "Root.h"
// gets instance of OutputHandler
// more code
I am getting errors regarding exitStatus, static bool instanceExists, and static class output being already defined by Root.obj in OutputHandler.obj. I assume the issue is with including the header file OutputHandler.h in both Root.h and OutputHandler.cpp. Anyone know how to fix this or how to better organize header files?
Because include guards only work at the translation unit level (you can, for this simple case, consider a single C file to be a translation unit).
That means a single C file, if it includes the header file twice, will not process it the second time due to the include guards.
However, if you include the header from two different C files, each of them will get a copy of the variables defined in that header.
Then, when you link them together, you get the duplicates.
The easiest way to get around this problem is to never define things in headers, only declare them.
So, in the header (eg, xyzzy.h), you have:
extern int xyzzy; // declare but don't define.
and in all the C files that want to use that, put:
$include "xyzzy.h"
and, in one of those C files, also put:
int xyzzy; // define it here, once.
You can think of declaration as a simple "I declare that this exists somewhere, just not here", while definition is "I an creating this here and now".
Declare extern usigned char exitStatus in Global.h and define it in one implementation file.
The problem is during the linking phase; include guards in the headers won't help you.
In C, there is the separate concepts of declarations and definitions. Declarations are what are put into headers; they merely state that a particular variable exists. The definition of a variable is where storage is actually allocated for it.
For example, in your Global.h, you have:
#ifndef Global_h
#define Global_h
#include <iostream>
usigned char exitStatus;
#endif
This is defining a variable called exitStatus, and the linker is complaining because any given variable should only be defined in one place in a program. What you need to do is declare it in the header, and then define it in only one place in a source (*.cpp) file. For example, your header should declare exitStatus with:
extern char exitStatus;
and in only one source file, define it with:
char exitStatus;
The situation is similar for output in Root.h, as well as any other place you should be declaring variables in the header file.
See also: http://www.cprogramming.com/declare_vs_define.html
I am making a small game.
In BattleRecord.h:
#ifndef _CHARACTER_H_
#define _CHARACTER_H_
#include "Character.h"
#endif
class BattleRecord
{
public:
Character Attacker;
Character Defender;
Status status;
int DamageDealt;
int GoldEarned;
int ExpGained;
};
In Character.h:
#ifndef _EQUIPMENT_H_
#define _EQUIPMENT_H_
#include "Equipment.h"
#endif
class BattleRecord;
class Character
{
BattleRecord AttackEnemy(Character &Enemy);
}
In BattleRecord.h:
#ifndef _CHARACTER_H_
#define _CHARACTEr_H_
#include "Character.h"
#endif
#ifndef _BATLE_RECORD_H_
#define _BATLE_RECORD_H_
#include "BattleRecord.h"
#endif
class GUI
{
public:
//GUI Methods, and two of these:
void ViewStats(Character &Player);
void Report(BattleRecord Record)
}
The problem here is, my Character.h and BattleRecord.h need to include each other, and this definitely will cause multiple redefinition problem. Therefore, I used forward declaration in Character.h by adding:
class BattleRecord;
The problem is sovled. But then, the GUI.h needs BattleRecord.h again for reporting the battle, so I have to include BattleRecord.h into the GUI.h. I also have to include the Character.h in order to pass into the ViewStat function. I got error and stuck with this up to this piont.
You're using inclusion guards wrong. They should appear in the file that you intend to prevent multiple inclusions only, and they should cover the entire file. (not just the includes).
For example, in BattleRecord.h
#ifndef _BATTLE_H_
#define _BATTLE_H_
#include "Character.h"
class BattleRecord
{
public:
Character Attacker;
Character Defender;
Status status;
int DamageDealt;
int GoldEarned;
int ExpGained;
};
#endif // _BATTLE_H_
Put your #endif at the end of the file not the end of your includes or use #pragma once at the top if your compiler supports this although that is less portable.
Edit:
To further explain what #ifdef & ifndef does is tell the compiler to include or exclude code entirely from compilation.
// if _UNQIUEHEADERNAME_H_ is NOT defined include and compile this code up to #endif
#ifndef _UNQIUEHEADERNAME_H_
// preprocessor define so next time we include this file it is defined and we skip it
#define _UNQIUEHEADERNAME_H_
// put all the code classes and what not that should only be included once here
#endif // close the statement
The reason you want to do this is because including a header file is basically saying "put all the code in this file here" if you did that multiple times then you'd have naming conflicts from redefining objects and slow compile times in the best scenario.
In general, use forward declaration instead of includes. This minimizes how many includes you include file contains. The only exception is when the class you are defining is a derived class, then you need to include the base class.
In addition to the include guard issues mentioned above (you also have a _CHARACTEr_H_/_CHARACTER_H_ mismatch that might cause you trouble on line 2 of GUI.h), you may want to revise your object design so that the Character does not AttackEnemy(), but rather there is a Battle() class where two Characters are referenced and a BattleRecord is produced after the battle. This would prevent the Character class from ever having to know about BattleRecords in the first place, would allow for the possibility of multi-Character battles in the future, having multi-turn battles, or having special battles through inheritance of the Battle class.
OK everyone,
Thanks for helping me. I have rewritten all the inclusions for the header files as suggested, and it works flawless now. Take quite time a bit of time since I did it wrong for many classes.