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Bison 1.875

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5.9 Stack Overflow, and How to Avoid It

The Bison parser stack can overflow if too many tokens are shifted and not reduced. When this happens, the parser function yyparse returns a nonzero value, pausing only to call yyerror to report the overflow.

Because Bison parsers have growing stacks, hitting the upper limit usually results from using a right recursion instead of a left recursion, See section Recursive Rules.

By defining the macro YYMAXDEPTH, you can control how deep the parser stack can become before a stack overflow occurs. 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. It must be a constant expression whose value is known at compile time.

The stack space allowed is not necessarily allocated. If you specify a large value for YYMAXDEPTH, the parser actually 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.

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. This value too must be a compile-time constant integer. The default is 200.

Because of semantical differences between C and C++, the LALR(1) parsers in C produced by Bison by compiled as C++ cannot grow. In this precise case (compiling a C parser as C++) you are suggested to grow YYINITDEPTH. In the near future, a C++ output output will be provided which addresses this issue.


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