BNF

In computer science, Backus–Naur form or Backus normal form (BNF) is a metasyntax notation for context-free grammars, often used to describe the syntax of languages used in computing, such as computer programming languages, document formats, instruction sets and communication protocols. 

BNF可用于描述各编程语言的语法，如描述C语言中的类型：

  

   

    

     

    
    

     

          <类型> ::= <简单类型> | <指针类型> | <自定义类型> 
     
    
   

    

     

    
    

     

      　　<指针类型> ::= <类型> *
     
    
   

    

     

    
    

     

      　　<简单类型> ::= int|char|double|float|long|short|void 
     
    
   

    

     

    
    

     

      　　<自定义类型> ::= enum<标识符>|struct<标识符>|union<标识符>|<标识符>
     
    
  
 

BNF的语法

BNF就是用来描述各语法的，所以BNF的语法是元语法。

　　< > : 内包含的为必选项。 
　　[ ] : 内包含的为可选项。 
　　{ } : 内包含的为可重复0至无数次的项。 
　　|  : 表示在其左右两边任选一项，相当于"OR"的意思。 
　　::= : 是“被定义为”的意思 
　　"..." : 术语符号 
 　　[...] : 选项，最多出现一次 
　　{...} : 重复项，任意次数，包括 0 次 
　　(...) : 分组 
　　|   : 并列选项，只能选一个
 

BNF自指

BNF's syntax itself may be represented with a BNF like the following:

 <syntax>         ::= <rule> | <rule> <syntax>
 <rule>           ::= <opt-whitespace> "<" <rule-name> ">" <opt-whitespace> "::=" <opt-whitespace> <expression> <line-end>
 <opt-whitespace> ::= " " <opt-whitespace> | ""
 <expression>     ::= <list> | <list> <opt-whitespace> "|" <opt-whitespace> <expression>
 <line-end>       ::= <opt-whitespace> <EOL> | <line-end> <line-end>
 <list>           ::= <term> | <term> <opt-whitespace> <list>
 <term>           ::= <literal> | "<" <rule-name> ">"
 <literal>        ::= '"' <text1> '"' | "'" <text2> "'"
 <text1>          ::= "" | <character1> <text1>
 <text2>          ::= '' | <character2> <text2>
 <character>      ::= <letter> | <digit> | <symbol>
 <letter>         ::= "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" | "J" | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" | "S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z" | "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | "j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z"
 <digit>          ::= "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
 <symbol>         ::=  "|" | " " | "!" | "#" | "$" | "%" | "&" | "(" | ")" | "*" | "+" | "," | "-" | "." | "/" | ":" | ";" | ">" | "=" | "<" | "?" | "@" | "[" | "\" | "]" | "^" | "_" | "`" | "{" | "}" | "~"
 <character1>     ::= <character> | "'"
 <character2>     ::= <character> | '"'
 <rule-name>      ::= <letter> | <rule-name> <rule-char>
 <rule-char>      ::= <letter> | <digit> | "-"

ps：本文内容实属东拼西凑，浅读，没太研究。

文章来源: blog.csdn.net，作者：csuzhucong，版权归原作者所有，如需转载，请联系作者。

原文链接：blog.csdn.net/nameofcsdn/article/details/120963134