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Re: Uninitialized integers and warnings
- From: Ian Lance Taylor <iant at google dot com>
- To: Umesh Kalappa <umesh dot kalappa0 at gmail dot com>
- Cc: Kirill Tkhai <tkhai at yandex dot ru>, GCC Development <gcc at gcc dot gnu dot org>
- Date: Thu, 5 Sep 2013 12:54:45 -0700
- Subject: Re: Uninitialized integers and warnings
- Authentication-results: sourceware.org; auth=none
- References: <154831378302042 at web21m dot yandex dot ru> <CAKOQZ8wVSTGjHUxrzbEbm8Lw2EpOVnNVmF6+X0-NhLk-_zDfJg at mail dot gmail dot com> <CAGfacvSQ4CiJoCOp+-aSVNuLW_=dNSqAkT8D4L2N2YMgmFdH4Q at mail dot gmail dot com> <CAKOQZ8y0qhh0JQu1gp9MvaLgd7mZ1ttUX1kNp=N+5BPCK+Uung at mail dot gmail dot com> <CAGfacvQ-C+XUHrVMwOKYbWQhXuGRn4B5DasD6wagVyL91JzYhg at mail dot gmail dot com>
On Wed, Sep 4, 2013 at 10:34 PM, Umesh Kalappa <umesh.kalappa0@gmail.com> wrote:
>>>>When p == 0 the program has undefined behaviour,
> Ian,What makes you to say this is undefined ?,Please can you elaborate more
> on this and again tried with below sample
>
>
> int func (int p)
> {
> int x;
> if (p != 1)
> x = 1;
> return x;
> }
When p == 1 the behaviour of this function is undefined.
C99 6.7.8 p10: "If an object that has automatic storage duration is
not initialized explicitly, its value is indeterminate."
C99 Annex J.2: "The behavior is undefined in the following
circumstances: ... — The value of an object with automatic storage
duration is used while it is indeterminate (6.2.4, 6.7.8, 6.8)."
Let me ask you: what makes you say that the behaviour of this function
is *not* undefined when p == 1?
> Still gcc return with 1 with 03 option and returns some junk with default
> run.Which is inconsistent or Did i missing something here ???
When the behaviour is undefined anything can happen. There is no
meaning to such a program.
Ian