Record some useful things personally think
lex program consists of three parts
statement
%%
Translation rules
%%
Auxiliary process
Part of the declaration and% {} are copied to the beginning of the generated C language portion between percent.
Translation rules:
Mode in the beginning of each line, followed by the C code is executed when the matching, using {} enclose. (Mode must be beginning of a line, starting with a blank line will be copied)
yytext always point to this match input text.
Mode Example
[A-Za-z] + is used to match a word, denoted as a character class brackets, which matches one or more + class.
. Dot represents any one character.
[^ \ T \ n] + at the symbol start portion of the character class ^ refers not match any character which character class.
"+" Is generally used to indicate a specific character or string matching.