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From: Bart Schaefer <schaefer@brasslantern.com>
Message-id: <141120090532.ZM3683@torch.brasslantern.com>
Date: Thu, 20 Nov 2014 09:05:32 -0800
In-reply-to: <546D4854.1030604@eastlink.ca>
Comments: In reply to Ray Andrews <rayandrews@eastlink.ca>
 "trying dputs" (Nov 19,  5:48pm)
References: <546D4854.1030604@eastlink.ca>
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To: Zsh hackers list <zsh-workers@zsh.org>
Subject: Re: trying dputs
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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.

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.