Also sprach Richard B. Johnson:
} On Tue, 29 Feb 2000, Bill Wendling wrote:
}
} > Depends on where the char str[12] is placed. If it is global, then it is
} > zeroed cause it's static...If it's an auto, then it can (and probably
} > does) have garbage after the terminating \0.
} >
}
} No! I showed exactly what happened. I did not guess, nor was it theory.
} I showed exactly what happens. The generated code is exact, explicit,
} absolute. It is not what 'C' is required to care about. It is not what
} some "rule" says. It is exactly and precisely what the 'C' compiler
} did with the code cited by one who submitted the sample.
}
} I simply explained what was happening. Now, if you don't think it should
} have done this then that's another matter. Since there is no known rule
} about what the compiler should have done it could have left it alone
} after the required terminating \0 or even written a copyright message in
} the remaining string space.
}
} Most real programmers would not have used such a construct because it
} requires that strings be duplicated. You need the string template
} someplace known only to the compiler, then it has to be copied at
} runtime to the place defined by the programmer. Normally one would
} use an initialized pointer or just a static string declaration.
}
>From the comp.lang.c FAQ:
Section 17. Miscellaneous
17.1: What can I safely assume about the initial values of variables
which are not explicitly initialized? If global variables start
out as "zero," is that good enough for null pointers and
floating-point zeroes?
A: Variables with "static" duration (that is, those declared
outside of functions, and those declared with the storage class
static), are guaranteed initialized to zero, as if the
programmer had typed "= 0". Therefore, such variables are
initialized to the null pointer (of the correct type) if they
are pointers, and to 0.0 if they are floating-point.
Variables with "automatic" duration (i.e. local variables
without the static storage class) start out containing garbage,
unless they are explicitly initialized. Nothing useful can be
predicted about the garbage.
Dynamically-allocated memory obtained with malloc and realloc is
also likely to contain garbage, and must be initialized by the
calling program, as appropriate. Memory obtained with calloc
contains all-bits-0, but this is not necessarily useful for
pointer or floating-point values (see question 3.11, and section
1).
Sorry to quote you chapter and verse, but your dressing down required it,
me thinks.
-- || Bill Wendling wendling@ganymede.isdn.uiuc.edu- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.rutgers.edu Please read the FAQ at http://www.tux.org/lkml/
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