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Date: Thu, 20 Nov 2014 09:27:23 -0800
From: Ray Andrews <rayandrews@eastlink.ca>
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To: zsh-workers@zsh.org
Subject: Re: trying dputs
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 <141120090532.ZM3683@torch.brasslantern.com>
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On 11/20/2014 09:05 AM, Bart Schaefer wrote:
> On Nov 19,  5:48pm, Ray Andrews wrote:
> }
> } If I steal 'opts->args' with a test string like this:
> }
> } //char *garbage = "utter garbage";
> } //ops->args = &garbage;
> }
> } ... I get what I expect from this:
> }
> } dputs("\nargs: %s", *(ops->args));
> }
> } ... but if I leave the pointer unmolested, I get a zsh
> } segmentation fault. Why is that?
>
> Because ops->args is a NULL pointer (not a pointer to an empty string)
> when there are no arguments to the option.  Dereferencing a NULL pointer
> is a segmentation fault in most cases; if you are used to getting "NULL"
> as output from printf("%s\n", (char *)0), then you've been damaged by an
> overly generous compiler or an overly protective OS.
If it's supposta be NULL when not in use, then I got what I should get, 
quite right.  I
just thought it might more safely point to a NULL string, but if that's 
not how it's
done, then it's probably for a good reason. I can't say otherwise.
>
> Look at the definitions of OPT_ARG and OPT_ARG_SAFE in zsh.h.  You should
> not be dereferencing ops->args directly, even in a debugging statement.
Ok.  Easy enough to test for a NULL pointer in any case.