多个定义符号C ++错误 [英] Multiple Defined Symbols C++ error
问题描述
我认为 ifndef的东西#define something body #endif 解决了这个错误，所以我不知道为什么会发生这种情况。
I thought ifndef something #define something body #endif solved this error, so I'm not sure why this is happening.
//Library.h
#ifndef __LIBRARY__
#define __LIBRARY__
#include <iostream>
#include <string>
#include <cstring>
#include <cmath>
#include <cstdio>
#include <cstdarg>
#include <vector>
#include <ctime>
#include <cmath>
#include <cstdlib>
//file includes
#include "Globals.h"
using namespace std;
#endif //__LIBRARY__
-
//globals.h
//global variables
#ifndef __GLOBAL__
#define __GLOBAL__
#include <vector>
#include <iostream>
#include <string>
//prototypes
bool Poglathon(std::vector<std::string>& text);
void NPCTalk(std::string const& speaker,std::vector<std::string> const& text);
void wait(double seconds);
//player stats
std::string name;
double str; //strength
double wis; //wisdom
double ref; //reflex
double hp; //health points
double i; //initiative
double inte; //intelligence
double c; //courage
int gold; //gold
int xp; //experience
int ap; //armour points
int wd; //weapon damage
int lvl; //level
int sp; //skill points
#endif //__GLOBAL__
cpp文件包含Library.h。
Then there's two other cpp files that include "Library.h".
推荐答案
问题是，在你的globals.h头文件，声明一组变量，默认情况下具有外部链接：即所有全局变量！
The problem is that in your globals.h header file, you're declaring a suite of variables that by default have external linkage: namely, all the globals!
当你在头文件中对函数进行原型化时， / em>一个函数，但不能定义。有相同的函数的多个声明是完全合法的，这就是为什么如果几个不同的文件所有 #include 同一个头并声明相同的功能，它是完美的。另一方面，如果在头文件中有全局变量，则定义这些变量。变量只能在C ++中定义一次（这被称为<一>定义规则），如果多个文件定义相同的变量或函数，它将导致链接器错误，因为链接器不知道版本使用。这是为什么，你不 #include .cpp文件，因为如果你做了，你会多次定义所有的功能导出的标题。
When you prototype a function in a header file, you are declaring a function, but not defining it. It's perfectly legal to have multiple declarations of the same function, which is why if several different files all #include the same header and declare the same function it's perfectly fine. On the other hand, if you have global variables in a header file, you are defining those variables. Variables can only be defined once in C++ (this is called the one-definition rule), and if multiple files define the same variable or function it will cause a linker error because the linker won't know which version to use. This is the reason, by the way, that you don't #include .cpp files, since if you did you'd multiply define all the functions exported by that header.
要解决此问题，您需要在标题中将这些变量定义更改为变量声明使用 extern 关键字：
To fix this problem, in the header you'll want to change those variable definitions to variable declarations by using the extern keyword:
//player stats
extern std::string name;
extern double str; //strength
extern double wis; //wisdom
extern double ref; //reflex
extern double hp; //health points
extern double i; //initiative
extern double inte; //intelligence
extern double c; //courage
extern int gold; //gold
extern int xp; //experience
extern extern int ap; //armour points
extern int wd; //weapon damage
extern int lvl; //level
extern int sp; //skill points
这将允许任何数量的文件 #include 这个头，因为它们都没有真正定义变量;他们只是声明变量将存在于某处。然后，你应该创建一个新的.cpp文件，可能是globals.cpp，它实际上定义了变量：
This will allow any number of files to #include this header, since none of them are actually defining the variables; they're just declaring that the variables will exist somewhere. Then, you should create a new .cpp file, probably globals.cpp, that actually defines the variables:
#include "globals.h"
std::string name;
double str; //strength
double wis; //wisdom
double ref; //reflex
double hp; //health points
double i; //initiative
double inte; //intelligence
double c; //courage
int gold; //gold
int xp; //experience
int ap; //armour points
int wd; //weapon damage
int lvl; //level
int sp; //skill points
这些是变量的实际定义，因为它们只存在于一个地方（globals.cpp），你将不会得到任何更多的链接器错误。
These are the actual definitions for the variables, and since they exist in just one place (globals.cpp) you won't get any more linker errors.
希望这有助于！
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