modification of strings

[D. Chadwick Gibbons]

        I believe my understanding is mislead when it comes to the
interpretation of string constants and the effect the standard library
functions can preform on them.  Insofar as I have been told, strings can not
be modified - note, the type char *blah = "this is a string"; not the everyday
normal strings we use.  This would appear that if you attempted to modify
their contents, you would either get a core dump of some various flavor, or
the program would ignore your request.

        In general, the function of strcat is defined as

                char *strcat(s, ct)
                char *s, *ct;

Where s is the original string you wish to add too, and ct is the string you
wish to append - as I'm sure you really didn't know that :)

        With that definition, consider the following artificial sequence

                char *blah = "meow";
                char *tmp;

                tmp = strcpy(blah, "grr, snarl, hiss");

I would think since the string 'blah' is considered to be nonmodifiable that
it would not be changed, but the result would be placed into tmp.  However, on
different systems, this provides different results:
        SCO XENIX/286 2.2.2     core dumps on next access of anytype to 'blah'
        SCO XENIX/386 2.3.2     gives various warning messages but treats
                                'blah' like a normal string
        BSD 4.2                 does random things
        AT&T System V r3        refuses to work on Thursdays, but acts like
                                XENIX/386 on others

Apparently, either the effect of strings is not yet defined in these
implementations, or, more likely, what I was taught is incorrect.

Enlightenment is welcomed.
-- 
D. Chadwick Gibbons, chad at lakesys.lakesys.com, ...!uunet!marque!lakesys!chad