Visual C++ 是否支持“严格别名"? [英] Does Visual C++ support "strict aliasing"?

问题描述

我最近惊讶地发现 C 和 C++ 语言标准有一个严格的别名"规则.本质上，该规则禁止不同类型的变量引用相同的内存位置.

I recently was surprised to learn that the C and C++ language standards have a "strict aliasing" rule. In essence, the rule prohibits variables of differing types from referencing the same memory location.

举个例子:

char buffer[4] = { 0x55, 0x66, 0x77, 0x88 };
int32 *p = (int32*)&buffer[0]; // illegal because buffer[0] and *p are different types

我接触过的大多数专业 C++ 开发人员都不熟悉这条规则.根据我的研究，它似乎主要影响 GCC/G++/CLANG 用户.Visual C++ 是否支持启用/禁用此规则?如果是这样，如何做到这一点?

Most of the professional C++ developers I interact with are not familiar with this rule. Based on my research, it seems to affect mostly GCC/G++/CLANG users. Does Visual C++ support enabling/disabling this rule? If so, how does one do so?

谢谢

推荐答案

严格别名"是限制程序的 C++ 规则，而不是编译器.由于违反规则是未定义行为，不需要诊断编译器不需要以任何方式支持它.

"Strict aliasing" is a C++ rule restricting programs, not compilers. Since violating the rule is Undefined Behavior, no diagnostic required a compiler doesn't need to support it in any way.

也就是说，微软在应用优化方面不太积极.直到上周，他们才宣布他们的新优化器 假设没有签名溢出，GCC 已经假设了几年.严格的别名会破坏一些 Windows 标头，因此需要先修复这些标头.(一些类型就像它们包含 union 一样，但它们并没有正式定义)

That said, Microsoft is a bit less aggressive in applying optimizations. Only last week have they announced their new optimizer assumes no signed overflow, something that GCC has assumed for a few years already. Strict aliasing is going to break a few Windows headers, so those need fixing first. (A few types act as if they contain unions, but they're not formally defined as such)

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