Non-constant initializers

Non-constant initializers

[Ross Alexander]

It seems that code like

#include <stdio.h>

FILE *f = stdin;

int main()
{
..
}

fail because of non-constant initializer.  This did not happen before.
Is there any way to tell egcs-980321 how to handle this, or should I
upgrade.

-- 
Ross Alexander                       r.alexander@auckland.ac.nz
Department of Statistics
University of Auckland
New Zealand

Re: Non-constant initializers

[Per Bothner]

> It seems that code like
> FILE *f = stdin;
> fail because of non-constant initializer.  This did not happen before.

Er, whether this works depends on whether the language or C or C++
(whcih you did not specify) and what the definition of stdin is in
your C libraries (which you also did not specify).

It is supposed to work in C++, and it is undefined whether it works
in C:  It depends on the definition of stdin.  Under traditional
Unix it works, because stdin is &_iob[0]; under many other systems
it doesn't.  This is not a bug in egcs or libc, but a bug in your code.

	--Per Bothner
Cygnus Solutions     bothner@cygnus.com     http://www.cygnus.com/~bothner

Re: Non-constant initializers

[Andreas Schwab]

Ross Alexander <r.alexander@auckland.ac.nz> writes:

|> It seems that code like
|> #include <stdio.h>

|> FILE *f = stdin;

|> int main()
|> {
|> ..
|> }

|> fail because of non-constant initializer.  This did not happen before.
|> Is there any way to tell egcs-980321 how to handle this, or should I
|> upgrade.

You should not write that.  ISO C does not require std{in,out,err} to be a
constant expression.  This has nothing to do with the compiler, it's a
library issue.

-- 
Andreas Schwab                                      "And now for something
schwab@issan.informatik.uni-dortmund.de              completely different"
schwab@gnu.org

Re: Non-constant initializers

[Mike Stump]

> To: Ross Alexander <r.alexander@auckland.ac.nz>
> From: Andreas Schwab <schwab@issan.informatik.uni-dortmund.de>
> Date: 22 Apr 1998 10:48:16 +0200

> Ross Alexander <r.alexander@auckland.ac.nz> writes:

> |> FILE *f = stdin;

> You should not write that.  ISO C does not require std{in,out,err}
> to be a constant expression.

Or, you can switch to C++.  It always allows that.  :-)

RE: Non-constant initializers

[Kaz Kylheku]

On Tuesday, April 21, 1998 5:14 PM, Ross Alexander 
[SMTP:r.alexander@auckland.ac.nz] wrote:
> It seems that code like
>
> #include <stdio.h>
>
> FILE *f = stdin;
>
> int main()
> {
> ..
> }
>
> fail because of non-constant initializer.  This did not happen before.
> Is there any way to tell egcs-980321 how to handle this, or should I
> upgrade.

You need to upgrade your program to valid C. Nowhere in the standard
is it required that ``stdin'' be a constant expression; hence your
program is ill formed.

For example, stdin could quite naturally be be a static object
declared as

	extern FILE *stdin;

after which stdin is anything but a constant expression.

C programs which depend on stdin or stdout to expand to
address constants are simply not portable.

Re: Non-constant initializers

[Ross Alexander]

> 
> > extern int *x;
> > int *y = x;
> 
> You say this works with C++, and doesn't work with C.
> Isn't that what I just said was how it was supposed to be?
> 
> > I can try and hunt down the problem but a few hints would come in handy.
> 
> There is no problem to track down.  Fix your code.

Sorry, I follow.  Unfortunately the behaviour

	FILE *blah = stdin;

is rather wide spread.  Normally this wouldn't matter that much but
both gnome and netscape are affected :-(.

I'll send them bug reports on the matter.

Again, many thanks for your time.
 
> 	--Per Bothner
> Cygnus Solutions     bothner@cygnus.com     http://www.cygnus.com/~bothner
> 


-- 
Ross Alexander                       r.alexander@auckland.ac.nz
Department of Statistics
University of Auckland
New Zealand