Visual Studio C ++编译器怪异的行为 [英] Visual Studio C++ compiler weird behaviour

问题描述

我只是想知道为什么这小段代码在 Visual Studio 中正确编译（并且没有警告）。也许结果与 GCC 和 Clang ，但很遗憾，我现在无法测试。

  struct T {
 int t; 
 T（）：t（0）{} 
}; 
 
 int main（）{
 T（i_do_not_exist）; 
 return 0; 
} 
  

解决方案

T（i_do_not_exist）; 是与 T i_do_not_exist; 相同含义的对象声明。

N4567§6.8 [stmt.ambig] p1

语法中含有 expression-statement 和声明 s：具有函数式显式类型转换（5.2.3）的表达式语句作为其最左子表达式可以与声明，其中第一个声明符以（）开头，在这种情况下， > 。

$

在声明中 TD 其中 D 的格式为

（D1）

所包含的声明器类型-id 与声明中所包含的 declarator-id 相同

T D1

括号不会改变嵌入的 declarator-id 类型，

I'm just curious to know why this small piece of code compiles correctly (and without warnings) in Visual Studio. Maybe the result is the same with GCC and Clang, but unfortunately I can't test them now.

struct T {
    int t;
    T() : t(0) {}
};

int main() {
    T(i_do_not_exist);
    return 0;
}

解决方案

T(i_do_not_exist); is an object declaration with the same meaning as T i_do_not_exist;.

N4567 § 6.8[stmt.ambig]p1

There is an ambiguity in the grammar involving expression-statements and declarations: An expression-statement with a function-style explicit type conversion (5.2.3) as its leftmost subexpression can be indistinguishable from a declaration where the first declarator starts with a (. In those cases the statement is a declaration.

§ 8.3[dcl.meaning]p6

In a declaration T D where D has the form

( D1 )

the type of the contained declarator-id is the same as that of the contained declarator-id in the declaration

T D1

Parentheses do not alter the type of the embedded declarator-id, but they can alter the binding of complex declarators.

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