问题
I came across the following program, which compiles without errors or even warnings:
int main(){
<:]{%>; // smile!
}
Live example.
What does the program do, and what is that smiley-expression?
回答1:
That's an empty lambda using a digraph disguise. Normal lambdas don't have beards.
回答2:
The program uses digraphs to represent the following:
[] {};
This is a lambda expression that does nothing. The corresponding symbols have these equivalents:
<: = [
%> = }
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. The combination of the characters that make up a digraph are processed as a single token. This in turn makes up for any insufficiently-equipped keyboards or other such hardware or software.
回答3:
The program is using digraphs, which allow C++ programming with keyboards (or text encodings) that may not have the characters C++ typically uses.
The code resolves to this:
int main(){
[]{}; // smile!
}
回答4:
int main(){ <:]{%>; // smile! }
It's basically a Lambda expression (Lambda expression is one of C++11 features) using digraphs (both digraphs and trigraphs works on C++):
[] {};
Using only digraphs:
<:]<%};
<:]<%%>;
[:>{%>; // like my cubic hat?
[:><%};
[:><%%>;
Mixing them with Trigraphs:
<:??)<%??>; // popeye
??(:>{??>; // pirate
来源:https://stackoverflow.com/questions/15736282/what-is-this-smiley-with-beard-expression