Introducing Flex-1

Lecture 1
Introducing Flex(1)

1.1 Flex programs

flex program consists of three sections, separated by %% lines.
The first section contains declarations and option settings.
The second section is a list of patterns and actions,
and the third section is C code that is copied to the generated scanner, usually small routines related to the code in the actions.
In the declaration section, code inside of %{ and %} is copied through verbatim near the beginning of the generated C source file.
In the second section, each pattern is at the beginning of a line, followed by the C code to execute when the pattern matches. The C code can be one statement or possibly a multiline block in braces, { }. (Each pattern must start at the beginning of the line, since flex considers any line that starts with whitespace to be code to be copied into the generated C program.)