为什么`int;`在C中编译好，但在C ++中编译不好？ [英] Why does `int ;` compile fine in C, but not in C++?

问题描述

请考虑以下程序（请参阅现场演示此处）。

Consider the following program (see live demo here).

#include <stdio.h>
int main(void)
{
      int ;  // Missing variable name
      puts("Surprise");
}

我的编译器gcc 4.8.1给出了下面的警告：

My compiler, gcc 4.8.1, gives the below warning:

警告无用的类型名称在空声明中[缺省情况下启用]

[Warning] useless type name in empty declaration [enabled by default]

为什么编译好？我不应该得到一个编译器错误？当我将它编译为C ++程序时，g ++ 4.8.1给出了以下错误：
$ b

Why does it compile fine? Shouldn't I get a compiler error? g++ 4.8.1 gives the following error when I compile it as a C++ program:

<错误>声明不声明任何东西[-fpermissive ]

[Error] declaration does not declare anything [-fpermissive]

推荐答案

The C standard says

除static_assert声明以外的声明应至少声明一个声明符（函数的参数或结构或联合的成员除外），标记或枚举的成员。

A declaration other than a static_assert declaration shall declare at least a declarator (other than the parameters of a function or the members of a structure or union), a tag, or the members of an enumeration.

C ++说明

C++ says

简单声明，只有在声明类（第9章）或枚举时，才可以省略可选的init-declarator-list。

In a simple-declaration, the optional init-declarator-list can be omitted only when declaring a class (Clause 9) or enumeration.

A违反这两种语言都需要诊断。标准不会谈论编译器错误或警告。警告是诊断。

A violation of this in either language requires a diagnostic. The standards do not talk about compiler errors or warnings. A warning is a diagnostic.

这篇关于为什么`int;`在C中编译好，但在C ++中编译不好？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！