为什么在同一声明区域内声明相同的名称被拒绝？ [英] Why does declaration of the same name inside the same declarative region is denied?

问题描述

以下代码无法编译：

#include <iostream>
#include <stdio.h>

int a=5;
char a='a';

int main(){ std::cout << a;}

这是因为：

test.cpp:5:6: error: conflicting declaration ‘char a’
test.cpp:4:5: error: ‘a’ has a previous declaration as ‘int a’

但是标准中指定的限制在哪里？我找不到它。请给我一个参考。

But where does this restriction specified in the standard? I can't find it. Please give me a reference.

推荐答案

这是对单一定义规则（ODR）的简单违反。参见n3797 S3.2 / 1。

This is a simple violation of the One Definition Rule (ODR). See n3797 S3.2/1.

无翻译单元应包含任何变量，函数，类类型，枚举类型，或模板。

No translation unit shall contain more than one definition of any variable, function, class type, enumeration type, or template.

真的没有什么可说的了。每一行都是 a （不是声明）的定义。

There really is no more to be said. Each of those lines is a definition of a (not a declaration). The program is ill-formed.

如果这些声明使用的是不同的翻译单元，程序仍然是不合格的，但适用的规则是不同的。见S3.5 / 10。

If these declarations were in different translation units the program would still be ill-formed, but the applicable rule is different. See S3.5/10.

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