Re: Valgrind reports possibly lost memory

[Thomas Dickey]

On Mon, May 30, 2022 at 03:24:43PM -0400, Steve Litt wrote:
> Thomas Dickey said on Mon, 30 May 2022 06:01:04 -0400
> 
> >On Mon, May 30, 2022 at 10:22:21AM +0200, TheJackiMonster wrote:
> 
> >> 
> >> Surprisingly running vim on my system which should use the same
> >> ncurses doesn't report any leakage at all.  
> >
> >vim uses the termcap interface (no initscr/endwin).
> 
> Is there documentation anywhere telling how to use the termcap
> interface and what its benefits and problems are?

man tgetent

DESCRIPTION
       These routines are included as a conversion aid for programs  that  use
       the  termcap  library.   Their parameters are the same and the routines
       are emulated using the terminfo database.  Thus, they can only be  used
       to  query  the  capabilities  of entries for which a terminfo entry has
       been compiled.

(writing tutorials is different from documenting things)

> >
> >Last year, there was some discussion about leaks in that,
> >after which perhaps Bram took my advice to use del_curterm().

fwiw, it started here:

https://invisible-island.net/ncurses/NEWS.html#index-t20210821

referring to the section of terminfo(5) beginning here:

https://invisible-island.net/ncurses/man/terminfo.5.html#h3-Parameterized-Strings

            The  terms  "static"  and "dynamic" are misleading.  Historically,
            these are simply two different sets of variables, whose values are
            not  reset  between calls to tparm(3x).  However, that fact is not
            documented in other implementations.  Relying on it will adversely
            impact portability to other implementations:

which involved allocating memory for each "SCREEN" to manage the variables.
 
> Is there documentation of how to use del_curterm in order to remove
> memory leak artifacts from ncurses?

Not exactly.  I explained to Bram that the termcap interface as such
doesn't provide a way to free memory, but that because it is on top
of terminfo, that calling del_curterm would be as good as he'd get
without using the debugging library.

Unlike the "SCREEN*", the terminfo interface has a convenient global variable:

       TERMINAL *cur_term;

though knowing what it's good for isn't necessarily crystal clear:

       The del_curterm routine frees the space pointed to by oterm  and  makes
       it available for further use.  If oterm is the same as cur_term, refer‐
       ences to any of the terminfo boolean,  numeric,  and  string  variables
       thereafter  may  refer  to  invalid  memory locations until another se‐
       tupterm has been called.

The exit_curses/exit_terminfo manpage doesn't mention delscreen and
del_curterm...

-- 
Thomas E. Dickey <dickey@invisible-island.net>
https://invisible-island.net
ftp://ftp.invisible-island.net

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