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Flex calls the functions yyalloc
, yyrealloc
, and yyfree
when it needs to allocate or free memory. By default, these functions are
wrappers around the standard C functions, malloc
, realloc
, and
free
, respectively. You can override the default implementations by telling
flex that you will provide your own implementations.
To override the default implementations, you must do two things:
// For a non-reentrant scanner void * yyalloc (size_t bytes); void * yyrealloc (void * ptr, size_t bytes); void yyfree (void * ptr); // For a reentrant scanner void * yyalloc (size_t bytes, void * yyscanner); void * yyrealloc (void * ptr, size_t bytes, void * yyscanner); void yyfree (void * ptr, void * yyscanner);
In the following example, we will override all three memory routines. We assume
that there is a custom allocator with garbage collection. In order to make this
example interesting, we will use a reentrant scanner, passing a pointer to the
custom allocator through yyextra
.
%{ #include "some_allocator.h" %} /* Suppress the default implementations. */ %option noyyalloc noyyrealloc noyyfree %option reentrant /* Initialize the allocator. */ %{ #define YY_EXTRA_TYPE struct allocator* #define YY_USER_INIT yyextra = allocator_create(); %} %% .|\n ; %% /* Provide our own implementations. */ void * yyalloc (size_t bytes, void* yyscanner) { return allocator_alloc (yyextra, bytes); } void * yyrealloc (void * ptr, size_t bytes, void* yyscanner) { return allocator_realloc (yyextra, bytes); } void yyfree (void * ptr, void * yyscanner) { /* Do nothing -- we leave it to the garbage collector. */ }
It
is not necessary to override all (or any) of the memory management routines.
You may, for example, override yyrealloc
, but not yyfree
or
yyalloc
.
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