Manual

Chapter 5: The Bison Parser Algorithm 81
5.9 Memory Management, and How to Avoid Memory
Exhaustion
The Bison parser stack can run out of memory if too many tokens are shifted and not
reduced. When this happens, the parser function yyparse calls yyerror and then returns
2.
Because Bison parsers have growing stacks, hitting the upper limit usually results from
using a right recursion instead of a left recursion, See Section 3.4 [Recursive Rules], page 45.
By defining the macro YYMAXDEPTH, you can control how deep the parser stack can
become before memory is exhausted. Define the macro with a value that is an integer.
This value is the maximum number of tokens that can be shifted (and not reduced) before
overflow.
The stack space allowed is not necessarily allocated. If you specify a large value for
YYMAXDEPTH, the parser normally allocates a small stack at first, and then makes it bigger by
stages as needed. This increasing allocation happens automatically and silently. Therefore,
you do not need to make YYMAXDEPTH painfully small merely to save space for ordinary
inputs that do not need much stack.
However, do not allow YYMAXDEPTH to be a value so large that arithmetic overflow could
occur when calculating the size of the stack space. Also, do not allow YYMAXDEPTH to be
less than YYINITDEPTH.
The default value of YYMAXDEPTH, if you do not define it, is 10000.
You can control how much stack is allocated initially by defining the macro YYINITDEPTH
to a positive integer. For the C LALR(1) parser, this value must be a compile-time constant
unless you are assuming C99 or some other target language or compiler that allows variablelength
arrays. The default is 200.
Do not allow YYINITDEPTH to be greater than YYMAXDEPTH.
Because of semantical differences between C and C++, the LALR(1) parsers in C produced
by Bison cannot grow when compiled by C++ compilers. In this precise case (compiling a
C parser as C++) you are suggested to grow YYINITDEPTH. The Bison maintainers hope to
fix this deficiency in a future release.