错误:"i"的外部声明在没有链接的声明之后 [英] error: extern declaration of 'i' follows declaration with no linkage

问题描述

在以下程序中，我认为 extern int i; 会将以下 i 更改为引用 i之外定义的 i >主要:

  #include< stdio.h>extern int i = 1;//警告:"i"已初始化并声明为"extern"int main(){int i = 2;printf(％d \ n"，i);外部诠释//错误:外部声明"i"跟随声明而没有链接printf(％d \ n"，i);返回0;} 

错误:'i'的外部声明跟随没有链接的声明"的原因是什么，其中没有链接的声明"是指 int i = 2; ?>

在删除 main 中的 int i = 2 后，

• 错误消失了，
• extern int i = 1; 上的警告警告:'i'已初始化并声明为'extern'" 也消失了.为什么会这样?

谢谢您的解释！

解决方案

一旦您在 main 函数中将一个名为 i 的变量定义为 i 被屏蔽，无法访问(除非您具有其地址).

当您以后添加声明 extern int i 时，这与在相同范围内名为 i 的局部变量冲突，因为局部变量无法具有外部链接.它没有不授予您访问全局 i 的权限.

当删除本地 i 时， extern int i 声明与文件范围内的定义匹配，因此没有错误.至于 extern int i = 1; 上的警告，在gcc 4.1.2上对我来说 not 并没有消失，所以这取决于编译器.

In the following program, I thought that extern int i; will change the following i to refer to the i defined outside main:

#include <stdio.h>

extern int i=1; // warning: 'i' initialized and declared 'extern'

int main()
{
    int i=2;
    printf("%d\n", i);
    extern int i; // error: extern declaration of 'i' follows declaration with no linkage
    printf("%d\n", i);
    return 0;
}

What is the reason of the "error: extern declaration of 'i' follows declaration with no linkage", where "declaration with no linkage" refers to int i=2;?

After I remove int i=2 in main,

• the error is gone,
• the warning "warning: 'i' initialized and declared 'extern'" on extern int i=1; also disappear . Why is that?

Thank you for explanations!

解决方案

Once you define a variable named i inside your main function, the i at file scope is masked and cannot be accessed (unless you have its address).

When you later add the declaration extern int i, this conflicts with the local variable named i at the same scope since locals can't have external linkage. It does not give you access to the global i.

When you remove the local i, the extern int i declaration matches up with the definition at file scope, so there is no error. As for the warning on extern int i=1;, that did not go away for me on gcc 4.1.2, so that depends on the compiler.

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