未初始化的常量

2022-01-23 00:00:00 visual-c++ g++ constants c++ default-constructor

使用当前的 MSVC 编译器可以完美编译:

This compiles perfectly fine with the current MSVC compiler:

struct Foo
{
} const foo;

但是，使用当前的 g++ 编译器编译失败:

However, it fails to compile with the current g++ compiler:

error: uninitialized const 'foo' [-fpermissive]
note: 'const struct Foo' has no user-provided default constructor

如果我自己提供一个默认构造函数，它会起作用:

If I provide a default constructor myself, it works:

struct Foo
{
    Foo() {}
} const foo;

这是 MSVC 过于宽松的另一种情况，还是 g++ 在这里过于严格?

Is this another case of MSVC being too permissive, or is g++ too strict here?

推荐答案

C++03标准:

8.5 [dcl.init] 第 9 段

如果没有为对象指定初始化器，并且对象是(可能是 cv 限定的)非 POD 类类型(或其数组)，则该对象应默认初始化；如果对象是 const 限定类型，则基础类类型应具有用户声明的默认构造函数.

If no initializer is specified for an object, and the object is of (possibly cv-qualified) non-POD class type (or array thereof), the object shall be default-initialized; if the object is of const-qualified type, the underlying class type shall have a user-declared default constructor.

从上面看 gcc 中的错误似乎是完全有效的.

From the above the error in gcc seems to be perfectly valid.

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