“……"的多重定义C
我有一个头文件USpecs.h":
I have a header file "USpecs.h":
#ifndef USPECS_H
#define USPECS_H
#include "Specs.h"
#include <iostream>
#include <vector>
std::vector<Specs*> UcakSpecs;
#endif
我在 main 函数和另一个名为 Ucak 的类中都使用了这个头文件.
I am using this header both in main function and another class named Ucak.
但是当我构建它时会发生以下错误:
But when i build it the following error occurs:
Ucak.cpp|6|`UcakSpecs'的多重定义|
Ucak.cpp|6|multiple definition of `UcakSpecs'|
正如我之前搜索的那样，#ifndef 应该可以，但事实并非如此.
As i searched before, it should be okay with #ifndef but it is not.
推荐答案
包含守卫仅防止在单个翻译单元(即具有包含标头的单个源文件)中出现多个定义.当您包含来自多个源文件的标头时，它们不会阻止多个定义.
The include guards only prevent multiple definitions within a single translation unit (i.e. a single source file with its included headers). They do not prevent multiple definitions when you include the header from multiple source files.
相反，您应该在标题中声明:
Instead, you should have a declaration in the header:
extern std::vector<Specs*> UcakSpecs;
在一个(也是唯一一个)源文件中定义:
and a definition in one (and only one) source file:
std::vector<Specs*> UcakSpecs;
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