使用extern int的LNK2001错误 [英] LNK2001 error using extern int

问题描述

我有一个简单的示例，我无法编译它:

I have this simple example and I can't get it to compile:

三个文件: my.h ， my.cpp 和 use.cpp :

//my.h
extern int foo;
void print_foo();
void print(int);

---

//my.cpp
#include "my.h"
#include "../../stb_lib_facilities.h" //inlcudes cout, cin, etc

void print_foo(){
    cout << foo << endl;
}

void print(int i){
    cout << i << endl;
}

---

//use.cpp
#include <iostream>
#include "my.h"

int main(){
    foo = 7;
    print_foo();
    print(99);

    return 0;
}

当我尝试编译它时，我收到三个错误:LNK2001:extern"int foo" ..LNK2019:extern"int foo" ..LNK1120:

When I try to compile it I get three errors: LNK2001: extern "int foo".. LNK2019: extern "int foo".. LNK1120:

我做错了什么?谢谢您的帮助

What am I doing wrong? Thanks for any help

推荐答案

您没有全局变量的任何定义.在任何 .cpp 文件中，但仅在其中一个文件中，您应该添加以下内容:

You do not have any definition of your global variable. In any of your .cpp files, but just in one of them, you should add this:

int foo = 0; // This is a definition

您的声明:

extern int foo; // This is a declaration

仅告诉编译器存在这样的全局变量，但是实际上没有地方可以定义它.因此，链接器最终会抱怨您有一个未定义的引用符号.

Only tells the compiler that such a global variable exists, but then there is no place where you actually define it. Therefore, the linker will eventually complain that you have an undefined referenced symbol.

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