单词是高级语言中有实在意义的最小语法单位，而单词又由字符组成。每一种高级语言都定义一组字符集。单词可大致分为五类：基本字，标识符，整常数，运算符，界限符。从输入的源程序字符串中逐个地把这些单词识别出来，并转化成机器比较容易使用的内码形式，这是词法分析器的主要任务。-The word is the smallest grammatical unit actual significance of the high-level language, the word characters. Each define a set of high-level language character sets. The word can be broadly divided into five categories: basic word identifier, integer constant, operator, boundary character. These words one by one from the input of the source string identified, and the form of internal code into the machine easier to use, which is the main task of the lexical analyzer.