Re: Interfaces.C.Strings chars_ptr memory management strategy

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 2018-06-03 10:03 PM, ytomino wrote:
> On Monday, June 4, 2018 at 4:33:20 AM UTC+9, Dmitry A. Kazakov wrote:
>> On 2018-06-03 20:31, ytomino wrote:
>>> Perhaps, malloc is better than New_String in this case.
>>>
>>>    function malloc (s : Interfaces.C.size_t) return Interfaces.C.Strings.chars_ptr
>>>       with Import, Convention => C;
>>
>> I had a case when that caused the application crashed.
>>
>> I guess it was because of mixed Visual Studio and GCC run-times. The
>> pointer returned by the malloc from one was freed in a third-party C
>> library by another.
>>
>> -- 
>> Regards,
>> Dmitry A. Kazakov
>> http://www.dmitry-kazakov.de
> 
> What!?
> 
> New_String calls malloc in the end, too, in mingw runtime.
> (It calls Memory_Alloc, Memory_Alloc is _gnat_malloc, and __gnat_malloc calls malloc.)
> https://gcc.gnu.org/svn/gcc/trunk/gcc/ada/libgnat/i-cstrin.adb
> https://gcc.gnu.org/svn/gcc/trunk/gcc/ada/libgnat/s-parame.ads
> https://gcc.gnu.org/svn/gcc/trunk/gcc/ada/libgnat/s-memory__mingw.adb
> 
> If Interfaces.C.Strings.Free (malloc) is crashed, New_String would be same.

No, not this free but the one called from the third-party library 
because the pointer was passed there to handle.

Of course it is safe to call malloc-free or New_String-Free pairs. Other 
combinations can be unsafe.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de