"?? *"C ++转义序列 [英] "??*" C++ escape sequence

问题描述

请注意，标题中的 * 是占位符，在我的案例中，罪魁祸首是 ?? [.

Note that the * in the title is meant to be a placeholder, in my case the culprit was ??[.

我刚刚遇到了由双问号组成的C ++(也称为"C")转义序列.这曾经是做什么用的，为什么还在那里呢?

I just came over C++ (also "C") escape sequences, formed by double question marks. What was this ever used for and why is it still there?

我有 ascii-85 编码的文本，很少出现双问号，只是花了一个下午试图在编码器/解码器中发现错误时，将头发从我的头上扯下来，而仅仅是编译器在骗我.

I have ascii-85 encoded text where double question marks seldom occur and just spent an afternoon ripping the hair from my head while attempting to find a bug in the encoder / decoder, while it was simply the compiler playing tricks on me.

推荐答案

根据C ++标准

2.4 Trigraph序列[lex.trigraph]

2.4 Trigraph sequences [lex.trigraph]

1在进行任何其他处理之前，以下三个字符序列之一(三字序列")的每次出现都被表1中所示的单个字符代替.表1 — Trigraph序列Trigraph替换Trigraph替换Trigraph替换

1 Before any other processing takes place, each occurrence of one of the following sequences of three characters ("trigraph sequences") is replaced by the single character indicated in Table 1. Table 1 — Trigraph sequences Trigraph Replacement Trigraph Replacement Trigraph Replacement

??= # ??( [ ??< {
??/ \ ??) ] ??> }
??’ ˆ ??! | ??- ~

但是，您显示的 ?? * 符号不是三部曲符号.因此很难说出它的意思.

However the symbol you showed ??* is not a trigraph symbol. So it is difficult to say what it means.

看来我已经明白了什么意思了.它们是通配符?和 * ，只是在字符串文字符号?中加倍了::)

It seems I have understood what it means. They are wild characters ? and * Simply inside a string literal symbol ? was doubled.:)

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