From: Eli Zaretskii <eliz@gnu.org>
To: dalanicola <mono.thwras@leadfactory.com.mx>
Cc: emacs-devel@gnu.org
Subject: Re: What iss the ecommmended
Date: Thu, 08 Feb 2024 20:53:47 +0200 [thread overview]
Message-ID: <86fry2wzwk.fsf@gnu.org> (raw)
In-Reply-To: <c97e3ba0-7795-41ee-8dac-83843b95d7c1@leadfactory.com.mx> (message from dalanicola on Thu, 8 Feb 2024 10:26:06 -0600)
> Date: Thu, 8 Feb 2024 10:26:06 -0600
> From: dalanicola <mono.thwras@leadfactory.com.mx>
>
> Subject: What is the recommended way to find out the number of arguments passed to a module function?
>
> I dispatchedd a material your way last day; were you able to obtain it?
>
> https://gkingmusik.com/oclue/?44904332
>
> -----------------------------------------------------------------------------
> I am tryiing to write dynamic module.
>
> In the module AP's 'make-funcction' we should pass a min-arity and a max-arity.
> However, it is unclear to me what is the recommended way to check for the number of
> arguments passd to some module function, as when not passing any argument, the 'optional' aargument does
> not seem
> to be nil, or any emacs-value at all (I have tested if it might be a NULL pointer). I have tested it using a
> 'test-module' with the following coe:
>
> #include <emacs-module.h>
> int plugin_is_GPL_compatible;
> static emacs_value
> test (emacs_env *env, ptrdiff_t nargs, emacs_value *args, void *data)
> {
> int integer = env->is_not_nil(env, args[0])? 1 : 0;
> return env->make_integer(env, integer);
> /* return args[0]; */
> }
> int
> emacs_module_init (struct emacs_runtime *runtime)
> {
> emacs_env *env = runtime->get_environment (runtime);
> emacs_value func = env->make_function (env, 0, 1, test, NULL, NULL);
> emacs_value symbol = env->intern (env, "test");
> emacs_value args = {symbol, func};
> env->funcall (env, env->intern (env, "defalias"), 2, args);
> return 0;
> }
>
> The 'test' function checks if the value of the argument is non-nil, and 'returns' a 1 if it is and a 0 otherwise. It
> works fine when paassing an argument, e.g. t or nil, but Emacs crashes when I don't pass an rgument. Also, I
> tried to simply return the value (by replacing the return line with the line in the comment below it), which
> returns the value successfully when I pass an argument, but again Emacs crashes when I don't pass any
> argument.
The correct way is to look at the value of the argument 'nargs'. Your
code should never access elements of the args[] array beyond
args[nargs-1], because the rest are not allocated, and your module
will crash if it accesses them. In particular, if nargs = 0, you
should not access the args[] array at all, since none of its elements
are allocated.
prev parent reply other threads:[~2024-02-08 18:53 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-08 16:26 What iss the ecommmended dalanicola
2024-02-08 18:53 ` Eli Zaretskii [this message]
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