Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uunet!dtgcube!ed
From: ed@uunet!dtgcube (Edward Jung)
Newsgroups: comp.sys.next
Subject: Re: Whats wrong?
Message-ID: <1989Nov29.101923.368@uunet!dtgcube>
Date: 29 Nov 89 10:19:23 GMT
References: <1989Nov29.014513.21386@csusac.csus.edu>
Organization: The Deep Thought Group, L.P.
Lines: 46
In-Reply-To: hoodr@syscube.csus.edu's message of 29 Nov 89 01:45:13 GMT

In article <1989Nov29.014513.21386@csusac.csus.edu> hoodr@syscube.csus.edu (Robert Hood) writes:

   I ran into a little problem. I have this piece of code that works on all
   the Unix boxes I could try, *EXCEPT* the NeXT:

[source code and other stuff deleted]

   Why?  Am I missing a compiler option somewhere? (I just used 'cc test.c')


Gnu's C compiler on the NeXT machine by default does not allow writable strings
for string constants (which is what you declare implicitly by using the quotes).
When you initialize a string from a constant, the string points to an unwritable
area of memory.  This is because the compiler will unique all the strings it
finds to save initializing string storage space.

To excerpt from the gcc docs:

   * GNU CC normally makes string constants read-only.  If several
     identical-looking string constants are used, GNU CC stores only one
     copy of the string.

     One consequence is that you cannot call `mktemp' with a string
     constant argument.  The function `mktemp' always alters the
     string its argument points to.

     Another consequence is that `sscanf' does not work on some
     systems when passed a string constant as its format control string.
     This is because `sscanf' incorrectly tries to write into the
     string constant.  Likewise `fscanf' and `scanf'.

     The best solution to these problems is to change the program to use
     `char'-array variables with initialization strings for these
     purposes instead of string constants.  But if this is not possible,
     you can use the `-fwritable-strings' flag, which directs GNU CC
     to handle string constants the same way most C compilers do.


So you can either set a compiler flag or change your declaration.  Note that
the traditional practice is really a bad one.

-- 
Edward Jung                             The Deep Thought Group, L.P.
BIX: ejung                                      3400 Swede Hill Road
NeXT or UNIX mail                                Clinton, WA.  98236
        UUCP: uunet!dtgcube!ed          Internet: ed@dtg.com