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I came across the following program, which compiles without errors or even warnings: 我遇到了以下程序，它编译时没有错误甚至是警告：

int main(){  <:]{%>; // smile!}

What does the program do, and what is that smiley-expression? 程序做了什么，笑脸表达是什么？

#1楼

参考：

#2楼

That's an empty lambda using a digraph disguise. 这是一个使用有向图伪装的空lambda。 Normal lambdas don't have beards. 普通的lambda没有胡须。

#3楼

The program uses to represent the following: 该程序使用来表示以下内容：

[] {};

This is a lambda expression that does nothing. 这是一个什么都不做的lambda表达式。 The corresponding symbols have these equivalents: 相应的符号具有以下等价物：

<: = [%> = }

Though they are generally unneeded today, digraphs are useful for when your keyboard lacks certain keys necessary to use C++'s basic source character set, namely the graphical ones. 虽然今天通常不需要它们，但是当键盘缺少使用C ++基本源字符集所必需的某些键时，有用图有用，即图形键。 The combination of the characters that make up a digraph are processed as a single token. 组成有向图的字符组合作为单个标记处理。 This in turn makes up for any insufficiently-equipped keyboards or other such hardware or software. 这反过来弥补了任何配备不充分的键盘或其他此类硬件或软件。

#4楼

The program is using , which allow C++ programming with keyboards (or text encodings) that may not have the characters C++ typically uses. 该程序使用 ，它允许使用可能没有C ++通常使用的字符的键盘（或文本编码）进行C ++编程。

The code resolves to this: 代码解析为：

int main(){  []{}; // smile!}

#5楼

int main(){ <:]{%>; // smile! }

It's basically a (Lambda expression is one of features) using (both digraphs and trigraphs works on C++): 它基本上是一个使用的 （Lambda表达式是特性之一）（有向图和三字符都适用于C ++）：

[] {};

Using only digraphs: 仅使用有向图：

<:]<%}; <:]<%%>;[:>{%>; // like my cubic hat?[:><%};[:><%%>;

Mixing them with Trigraphs: 将它们与Trigraphs混合：

<:??)<%??>; // popeye??(:>{??>; // pirate

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