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The Prologue section contains macro definitions and declarations
of functions and variables that are used in the actions in the grammar
rules. These are copied to the beginning of the parser implementation
file so that they precede the definition of yyparse
. You can
use ‘#include’ to get the declarations from a header file. If
you don’t need any C declarations, you may omit the ‘%{’ and
‘%}’ delimiters that bracket this section.
The Prologue section is terminated by the first occurrence of ‘%}’ that is outside a comment, a string literal, or a character constant.
You may have more than one Prologue section, intermixed with the
Bison declarations. This allows you to have C and Bison
declarations that refer to each other. For example, the %union
declaration may use types defined in a header file, and you may wish to
prototype functions that take arguments of type YYSTYPE
. This
can be done with two Prologue blocks, one before and one after the
%union
declaration.
%{ #define _GNU_SOURCE #include <stdio.h> #include "ptypes.h" %}
%union {
long int n;
tree t; /* tree
is defined in ptypes.h. */
}
%{ static void print_token_value (FILE *, int, YYSTYPE); #define YYPRINT(F, N, L) print_token_value (F, N, L) %}
…
When in doubt, it is usually safer to put prologue code before all
Bison declarations, rather than after. For example, any definitions
of feature test macros like _GNU_SOURCE
or
_POSIX_C_SOURCE
should appear before all Bison declarations, as
feature test macros can affect the behavior of Bison-generated
#include
directives.
Next: Prologue Alternatives, Up: Grammar Outline [Contents][Index]