Structure of A Lex File
The structure of a Lex file is intentionally similar to that of a yacc file; files are divided into three sections, separated by lines that contain only two percent signs, as follows:
Definition section %% Rules section %% C code section- The definition section defines macros and imports header files written in C. It is also possible to write any C code here, which will be copied verbatim into the generated source file.
- The rules section associates regular expression patterns with C statements. When the lexer sees text in the input matching a given pattern, it will execute the associated C code.
- The C code section contains C statements and functions that are copied verbatim to the generated source file. These statements presumably contain code called by the rules in the rules section. In large programs it is more convenient to place this code in a separate file linked in at compile time.
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