[PD-dev] How to free memory of t_symbol

[Christof Ressi]

Thanks :-D

BTW, Symbols in sclang work the same way. Also, they are frequently used 
in scripting languages. In this context, this is also referred to as 
"string interning", see https://en.wikipedia.org/wiki/String_interning

Christof

On 22.02.2024 15:38, Pierre Alexandre Tremblay wrote:
> This is by far the best explanation of symbols I’ve read, ever.
>
> Thanks!
>
>> On 22 Feb 2024, at 13:41, Christof Ressi <info at christofressi.com> wrote:
>>
>> Hi,
>>
>> Pd symbols are immutable and permanent. `gensym("foo")` looks if the symbol "foo" already exists; if yes, it just returns it, otherwise it creates a new symbol, adds it to the global symbol table and finally returns it.
>>
>> You must never attempt to free a symbol!
>>
>>> ```
>>> t_symbol **x_weights_arrays;
>>> t_symbol *x_biases_array;
>>> ```
>> Here you must only free `x_weights_array`, which is an array of `t_symbol*`, but not the `t_symbol*` elements themselves.
>>
>> ---
>>
>> Side note: since symbols are unique and persistent, they can be compared *by address*. In other words, two symbols are equal if they have the same address. This is different from ordinary C-strings which may reside at different memory locations and thus need to be compared with `strcmp()` (or equivalent functions).
>>
>> Christof
>>
>> On 22.02.2024 10:19, Alexandros Drymonitis wrote:
>>> I have a data structure with a symbol and an array of symbols that store array names defined as:
>>>
>>> ```
>>> t_symbol **x_weights_arrays;
>>> t_symbol *x_biases_array;
>>> ```
>>>
>>> When I'm done with them, I want to free the memory, but calling free(x_biases_array) doesn't seem to work, and once called, as soon as I try to do something else in Pd (like unlock the patch and choose an object), Pd crashes.
>>>
>>> I have narrowed down the error to freeing these symbols, and I'm sure the crash is not caused by something else. I scanned m_pd.h to see if there is a function to free t_symbol memory, but didn't seem to find anything. This might be something obvious for C-savvy people, but I'm not one, so any advice is welcome.
>>>
>>>
>>>
>>>
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>>
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