The macro processor
must be installed wherever flex is installed.
flex invokes ‘m4’, found by searching the directories in the
PATH environment variable. Any code you place in section 1 or in the
actions will be sent through m4. Please follow these rules to protect your
code from unwanted
m4macro names. If for some reason you need m4_ as a prefix, use a preprocessor #define to get your symbol past m4 unmangled.
x[y[z]]. The solution is simple. To get the literal string
"]""]". To get the array notation
x[y[z] ]. Flex will attempt to detect these sequences in user code, and escape them. However, it's best to avoid this complexity where possible, by removing such sequences from your code.
m4 is only required at the time you run
flex. The generated
scanner is ordinary C or C++, and does not require
 The use of m4 is subject to change in future revisions of flex. It is not part of the public API of flex. Do not depend on it.