C/C++字符串文字中的未知元字符?

你所看到的被称为 trigraph

默认情况下,GCC忽略三角图,因为几乎没有人故意使用它们。使用 -trigraph 选项,或告诉编译器使用 -Wtrigraphs

/Zc:trigraphs

避免trigraph意外的简单方法:将“?”字符串文本一分为二:

char* strange = "(Strange??)";
char* strange2 = "(Strange?" "?)";
/*                         ^^^ no punctuation */

编辑
-Wtrigraphs (已启用) -Wall

引用标准

    5.2.1.1 Trigraph sequences
1   Before any other processing takes place, each occurrence of one of the
    following sequences of three characters (called trigraph sequences13))
    is replaced with the corresponding single character.
           ??=      #               ??)      ]               ??!      |
           ??(      [               ??'      ^               ??>      }
           ??/      \               ??<      {               ??-      ~
    No other trigraph sequences exist. Each ? that does not begin one of
    the trigraphs listed above is not changed.

    5.1.1.2 Translation phases
1   The precedence among the syntax rules of translation is specified by
    the following phases.
         1.   Physical source file multibyte characters are mapped, in an
              implementation-defined manner, to the source character set
              (introducing new-line characters for end-of-line indicators)
              if necessary. Trigraph sequences are replaced by corresponding
              single-character internal representations.

这是一个 Trigraph !

trigraph

那是 trigraph

char* strange = "(Strange?\?)";

这是一个 trigraph .

Trigraphs 这就是原因。文中的C语言也适用于C++

如前几次所述,你被三角描记器咬伤了。有关更多信息,请参见上一个SO问题:

• Purpose of Trigraph sequences in C++?

您可以通过使用“?”字符的“\?”转义序列来解决此问题:

char* strange = "(Strange\?\?)";

事实上,这就是逃逸序列的原因,如果你不知道那些该死的三角图,这就有点神秘了。

当试图在GCC上交叉编译时,它将我的序列作为 trigraph :

所以我现在需要做的就是找出如何在默认情况下在项目中禁用它,因为我只能看到它给我带来了问题(我使用的是美国键盘布局)