在VC 2015上将宏与字符串一起使用失败

问题描述

为什么无法编译?

char programDate[] = "("__DATE__")";

但这可以很好地编译(请参见空格):

But this compiles fine (see space):

char programDate[] = "(" __DATE__")";

我知道VC2015现在支持文字运算符.但是那不应该在编译阶段吗? __DATE__应该已经被预处理程序处理过.这是怎么回事?

I do know VC2015 now supports literal-operators. But shouldn't that be in compilation phase? __DATE__ should have been processed by the pre-processor. What is going on here?

我想到了Unicode/非Unicode构建中的一些混合匹配问题-但这无济于事.这不仅与预定义的宏有关，而且与用户定义有关:

I thought of some mix-match issue with Unicode/non-Unicode build - but it doesn't help. It's not just issue with pre-defined macros, but with user defined also:

#define MACRO "abc"
char data[] = "("MACRO")";

Error C3688 invalid literal suffix '__DATE__'; literal operator or literal operator template 'operator ""__DATE__' not found

推荐答案

自C ++ 11起，用户定义的文字存在并且是预处理的一部分.语法是:

Since C++11, user-defined literals exist and are part of preprocessing. The grammar is:

preprocessing-token:
    user-defined-string-literal
    // other stuff...

user-defined-string-literal:
    string_literal ud-suffix

ud-suffix:
    identifier

因此"("__DATE__与 preprocessing-token 匹配，但是"(" __DATE__不匹配(这是两个单独的预处理令牌).

So "("__DATE__ matches preprocessing-token, but "(" __DATE__ doesn't (that is two separate preprocessing tokens).

宏替换发生在标记化之后.由于在您的第一个示例中没有令牌__DATE__，所以没有替代.

Macro replacement happens after tokenization. Since there is no token __DATE__ in your first example, there is no replacement.

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