Problem: scanf used for double

[Frank Chow]

Please see the following code:

/* main.c */

#include <stdio.h>

int main()
{
double d;
scanf("%f", &d);
printf("%g\n", d);
}

The problem is, whatever I input to stdin (even an illegal data), the
program just print a number that seems to be a data from "raw memory",
ie uninitialized memory (for example: "5.35162e-315").

And if I replace the statement "double d" with "double d = 3.14", then
I'll always get the output "3.14" for whatever I input (even an
illegal data).

Then I may get the conclusion that the "scanf" statement never does
its job. And I have tried this under 3 compilers and none of them give
the right result.

Please give me some explanation about this.

Thanks.

[Christopher Benson-Manica]

Irrwahn Grausewitz <ir*******@free net.de> spoke thus:

Nope, according to ISO/IEC 9899:1999 5.1.2.2.3 and 7.20.4.3#5
it is perfectly portable.

<dumb>So if 0 is portable, why the EXIT_SUCCESS macro?</dumb>

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cybers pace.org | don't, I need to know. Flames welcome.

[Irrwahn Grausewitz]

Christopher Benson-Manica <at***@nospam.c yberspace.org> wrote:

Irrwahn Grausewitz <ir*******@free net.de> spoke thus:

Nope, according to ISO/IEC 9899:1999 5.1.2.2.3 and 7.20.4.3#5
it is perfectly portable.

<dumb>So if 0 is portable, why the EXIT_SUCCESS macro?</dumb>

Because it's more descriptive and has a portable(!) and descriptive
counter-part, EXIT_FAILURE.

ISO/IEC 9899:1999 7.20.4.3
5 [...] If the value of status is zero or EXIT_SUCCESS, an
implementation-defined form of the status successful termination is
returned. If the value of status is EXIT_FAILURE, an implementation-
defined form of the status unsuccessful termination is returned.
Otherwise the status returned is implementation-defined.

Regards
--
Irrwahn
(ir*******@free net.de)

[Christopher Benson-Manica]

Irrwahn Grausewitz <ir*******@free net.de> spoke thus:

Because it's more descriptive and has a portable(!) and descriptive
counter-part, EXIT_FAILURE.

So it's kind of like the unary + thing, symmetry and all? I dunno, I always
thought the l337-ness of C code was directly related to how obfuscated it
looked ;)

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cybers pace.org | don't, I need to know. Flames welcome.

[Irrwahn Grausewitz]

Christopher Benson-Manica <at***@nospam.c yberspace.org> wrote:

Irrwahn Grausewitz <ir*******@free net.de> spoke thus:

Because it's more descriptive and has a portable(!) and descriptive
counter-part, EXIT_FAILURE.
So it's kind of like the unary + thing, symmetry and all?

Hm, well, yes and no. I can remember a discussion about this in c.l.c
or c.s.c, where the claim was made that in the context of program exit
codes 0 may describe a kind of successful termination different from
what EXIT_SUCCESS results in. Whatever that means, practically.
I dunno, I always
thought the l337-ness of C code was directly related to how obfuscated it
looked ;)

:)

Regards
--
Irrwahn
(ir*******@free net.de)

[Dan Pop]

In <bm**********@c hessie.cirr.com > Christopher Benson-Manica <at***@nospam.c yberspace.org> writes:

Irrwahn Grausewitz <ir*******@free net.de> spoke thus:

Because it's more descriptive and has a portable(!) and descriptive
counter-part, EXIT_FAILURE.

So it's kind of like the unary + thing, symmetry and all?

Exactly.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de

[Dan Pop]

In <gb************ *************** *****@4ax.com> Irrwahn Grausewitz <ir*******@free net.de> writes:

Christopher Benson-Manica <at***@nospam.c yberspace.org> wrote:

Irrwahn Grausewitz <ir*******@free net.de> spoke thus:

Because it's more descriptive and has a portable(!) and descriptive
counter-part, EXIT_FAILURE.

So it's kind of like the unary + thing, symmetry and all?

Hm, well, yes and no. I can remember a discussion about this in c.l.c
or c.s.c, where the claim was made that in the context of program exit
codes 0 may describe a kind of successful termination different from
what EXIT_SUCCESS results in. Whatever that means, practically.

Nothing at all, in the context of portable programming. Furthermore, the
most natural interpretation of the standard is that both are mapped to
the *same* form of successful termination.

5 Finally, control is returned to the host environment. If the
value of status is zero or EXIT_SUCCESS, an implementation-defined
^^
form of the status successful termination is returned.

The standard talks about a *single* "implementa tion-defined form of
the status successful termination".

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de

[Irrwahn Grausewitz]

Da*****@cern.ch (Dan Pop) wrote:

In <gb************ *************** *****@4ax.com> Irrwahn Grausewitz <ir*******@free net.de> writes:

<snip>

Hm, well, yes and no. I can remember a discussion about this in c.l.c
or c.s.c, where the claim was made that in the context of program exit
codes 0 may describe a kind of successful termination different from
what EXIT_SUCCESS results in. Whatever that means, practically.

Nothing at all, in the context of portable programming. Furthermore, the
most natural interpretation of the standard is that both are mapped to
the *same* form of successful termination.

5 Finally, control is returned to the host environment. If the
value of status is zero or EXIT_SUCCESS, an implementation-defined
^^
form of the status successful termination is returned.

The standard talks about a *single* "implementa tion-defined form of
the status successful termination".

It's the most natural interpretation, I agree. I just remembered the
discussion, not the outcome...

--
Irrwahn
(ir*******@free net.de)