(flex.info.gz) Overriding The Default Memory Management

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 21.2 Overriding The Default Memory Management
 =============================================
 
 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:
 
   1. Suppress the default implementations by specifying one or more of
      the following options:
 
         * `%option noyyalloc'
 
         * `%option noyyrealloc'
 
         * `%option noyyfree'.
 
   2. Provide your own implementation of the following functions: (1)
 
 
           // 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. */
      }
 
    ---------- Footnotes ----------
 
    (1) 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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(flex.info.gz) The Default Memory Management

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(flex.info.gz) A Note About yytext And Memory