1. trigraph三字符组
据说是为了照顾旧式键盘&＃xff0c;还是为了键盘坏了&＃xff0c;或者是使用非ASCII字符编码的语言输入方便&＃xff0c;设计了一些三元字符组&＃xff0c;两个问号加一个符号在预处理时替换为一个字符。MSDN这么解释
The source character set of C source programs is contained within the 7-bit ASCII character set but is a superset of the ISO 646-1983 Invariant Code Set. Trigraph sequences allow C programs to be written using only the ISO (International Standards Organization) Invariant Code Set.
这些三字符组有
| Trigraph replacement | Trigraph replacement | Trigraph replacement |
| ??&＃61; # | ??( [ | ??< { |
| ??/ / | ??) ] | ??> } |
| ??’ ^ | ??! | | ??- ~ |
2. alternative tokens
下面几对符号等价
| Alternative Primary | Alternative Primary | alternative Primary |
| <% { | and && | and_eq &&＃61; |
| %> } | bitor | | or_eq |&＃61; |
| <: [ | or || | xor_eq ^&＃61; |
| :> ] | xor ^ | not ! |
| %: # | compl ~ | not_eq !&＃61; |
| %:%: ## | bitand & | |
于是下面的程序就是合法的C&＃43;&＃43;程序&＃xff0c;而且很标准&＃xff1a;
??&＃61;include
int suM(int a, int b)
<%
int arr<:2:>;
arr<:0:> &＃61; a,
arr<:1 ??/
:> &＃61; b;
return arr??(0:> &＃43; arr??(1];
%>
int main(int argc, char* argv[])
??<
bool bv &＃61; false;
std::cout<<"Program name:"< if( ( bv ??! 1 and 1) not_eq false){
int iv &＃61; 1333;
std::cout<}
std::cout<<"3&＃43;4&＃61;"< return 0;
??>
用GCC编译的时候加上-trigraphs 选项即可&＃xff0c;VC默认编译不通过&＃xff0c;可能需要编译选项&＃xff0c;暂时还没找到
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