为什么 VS 不为逻辑运算符定义替代标记?

问题描述

替代令牌有效 c++ 关键字，但在 Visual Studio 2013 中，以下内容会发出编译错误(未声明的标识符):

Alternative tokens are valid c++ keywords, yet in Visual Studio 2013 the following emits a compilation error (undeclared identifier):

int main(int argc, const char* argv[])
{
    int k(1), l(2);
    if (k and l) cout << "both non zero
";

    return 0;
}

既然and or not 已经存在了很长一段时间，是否有理由不实施它们?

Since and or not have been around for quite some time, is there a reason for not implementing them?

推荐答案

您询问基本原理.这是一个可能的原因，不一定是对 Visual C++ 团队影响最大的原因:

You ask about the rationale. Here's one possible reason, not necessarily the one that most influenced the Visual C++ team:

1. 那些是 C 中的有效标识符.
2. 长期以来，Microsoft 一直建议对 C 和 C++ 代码使用 C++ 模式，而不是维护现代 C 编译器.
3. 如果将它们编译为关键字，使用这些作为标识符的有效 C 代码将无缘无故地中断.
4. 尝试编写可移植 C++ 的人大多使用 /permissive- 或 /Za 以实现最大的一致性，这将导致它们被视为关键字.
5. 通过包含头文件将它们视为 /Ze 中的关键字的解决方法是简单且可移植的.(G++ 的解决方法 -fno-operator-names 也不错，但是将选项放在源代码中而不是构建系统中会更好一些.)

1. Those are valid identifiers in C.
2. Microsoft's recommendation has long been to use C++ mode for both C and C++ code, rather than maintaining a modern C compiler.
3. Valid C code using these as identifiers would gratuitously break if they were compiled as keywords.
4. People trying to write portable C++ are mostly using /permissive- or /Za for maximum conformance anyway, which will cause these to be treated as keywords.
5. The workaround to treat them as keywords in /Ze by including a header file is easy and portable. (G++'s workaround -fno-operator-names isn't bad either, but putting the option in the source code rather than the build system is somewhat nicer.)

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