Istvan,

when querying a global variable that doesn't exist (yet), would it be 
possible to
return NULL, so that code can check if it exists?

I need this type of facility for pvsys_release() (pvfileio.c) as it is 
called from
memRESET() at times when a global variable has not yet been created (you
can check the code yourself). I have commented the call out for the moment,
but I think it might need to be put back later on.

Victor

Victor Lazzarini
Music Technology Laboratory
Music Department
National University of Ireland, Maynooth 



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Victor Lazzarini wrote:

> when querying a global variable that doesn't exist (yet), would it be 
> possible to
> return NULL, so that code can check if it exists?

It is already implemented that way, if you use csoundQueryGlobalVariable().
There are two functions for getting the address of a variable:

csoundQueryGlobalVariableNoCheck():

   fast version that does not check if the variable exists; if it does not,
   the operation of the function is undefined (which includes the possibility
   of a crash, or returning a wrong address).

csoundQueryGlobalVariable():

   safe, but slower function that returns NULL if the variable does not exist

Here is the source code of the functions so you can see the difference:

/**
  * Get pointer to space allocated with the name "name".
  * Returns NULL if the specified name is not defined.
  */
PUBLIC void *csoundQueryGlobalVariable(void *csound, const char *name)
{
     ENVIRON               *csnd = (ENVIRON*) csound;
     GlobalVariableEntry_t *p;
     unsigned char         h;
     /* check if there is an actual database to search */
     if (csnd->namedGlobals == NULL)
       return NULL;
     /* check for a valid name */
     if (name == NULL)
       return NULL;
     if (name[0] == '\0')
       return NULL;
     /* calculate hash value */
     h = name_hash(name);
     /* search tree */
     p = (GlobalVariableEntry_t*) (csnd->namedGlobals[(int) h]);
     if (p == NULL)
       return NULL;
     while (sCmp(name, (char*) (p->name)) != 0) {
       p = (GlobalVariableEntry_t*) p->nxt;
       if (p == NULL)
         return NULL;
     }
     return (void*) (p->p);
}

/**
  * This function is the same as csoundQueryGlobalVariable(), except the
  * variable is assumed to exist and no error checking is done.
  * Faster, but may crash or return an invalid pointer if 'name' is
  * not defined.
  */
PUBLIC void *csoundQueryGlobalVariableNoCheck(void *csound, const char *name)
{
     ENVIRON               *csnd = (ENVIRON*) csound;
     GlobalVariableEntry_t *p;
     unsigned char         h;

     /* calculate hash value */
     h = name_hash(name);
     /* search tree */
     p = (GlobalVariableEntry_t*) (csnd->namedGlobals[(int) h]);
     while (p->nxt != NULL && sCmp(name, (char*) (p->name)) != 0)
       p = (GlobalVariableEntry_t*) p->nxt;
     return (void*) (p->p);
}


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