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Re: Program received signal SIGSEGV, Segmentation fault.

From: Bruce Korb
Subject: Re: Program received signal SIGSEGV, Segmentation fault.
Date: Sat, 17 Nov 2012 12:22:15 -0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121025 Thunderbird/16.0.2

Hi Noah, Mark,

On 11/16/12 18:19, Noah Lavine wrote:
>     OK, so I tried latin1, too.  (replacing scm_from_utf3_string with
>     scm_from_latin1_string).  That also does not work.  It replaced the
>     0xA9 character with '?'.
> I am no expert on character encodings, but we've seen errors like this before 
> where it turned out that Guile was attempting to display the character on a 
> terminal which didn't support it, and then the terminal converted it into '?'.

I actually do not use Guile to output anything.
I give Guile a string with either the "define" or "set!" functions
and later pull them out with the verboten function scm_i_string_chars.
As far as I can tell, I have to call this procedure myself because
all other paths seem to lead through u8_uctomb, which is not
helpful for my application.

> Could there have been some change in how Guile displays strings that caused 
> this error? Did it used to show a \-escape sequence?

I have always called some function to obtain the text.
I understand the memory is not stable, so I immediately copy
the text out and forget the returned address.  Much like what
scm_to_utf8_stringn() does, but without going through the
u8_uctomb_aux transmogrifier.  I tend to use memcpy or fwrite.

>     What it all boils down to is that
>     I am looking for string handling functions that will handle the
>     NUL terminated list of bytes and keep its nose out of the contents
>     of the string.  Period.  Full stop.
> Could you explain what you're trying to do a little more?

Read input text, modify it according to some embedded markups,
inserting some auxiliary text gotten from another file, and
emitting the result.  95% of it is for computer program text.
The remainder is for man pages and texi docs.

Sometimes, people like to insert a copyright character in their
program text.  About a decade ago, someone asked me to do
something that would verify that a particular file was pure and
proper text and that copyright characters were okay.  This meant
that the "file" program was insufficient.  I rebuilt my library
of old stuff and my current autogen choked and died.

So here I am investigating the cause.

> If you're calling a function that looks at characters on a string 
> object that doesn't contain valid characters, then it will fail.

The only invalid character in my tiny little world is the NUL byte.

> ... So do you intend to make a 
> string object and then never look inside?

I look inside for a limited set of reasons:

1. to write it to output
2. to move it someplace else
3. to compare it against another sequence of bytes

> Or are you going to 
> roll your own string-handling starting from byte sequences?

I do not want to do this, but I will if I have to.

I really do not want to mess with transforming character sets on my
input and output.  Just read in, adjust as directed, and write.

Thank you for any help on using the Guile interface properly!

Regards, Bruce

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