“……"的多重定义C

问题描述

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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