6.32. yydebug and YYDEBUG

Bison can optionally compile in trace code that reports everything that the parser does. These reports are extremely verbose but are often the only way to figure out what a recalcitrant parser is doing.

6.32.1. YYDEBUG

Since the trace code is large and slow, it is not automatically compiled into the object program. To include the trace code, either use the -t flag on the bison command line or else define the C preprocessor symbol YYDEBUG to be nonzero either on the C compiler command line or by including something like this in the definition section: