compile-error: stdin is not a constant

compile-error: stdin is not a constant

[Wolfgang Haeuptli]

Hello people

sorry for the (probably) basic question...

Since I installed R5, some programs (that used to compile OK on R4) 
complain about : 

initializer element for 'foo' is not constant

while compiling constructs like:

FILE *foo = stdin;   (or FILE *foo = {(FILE *) stdin};  )

when I replaced this line with: FILE *foo = STDIN_FILENO; 
( defined in unistd.h), compilation works, but the resulting program
segfaults...

Any hints to make this work would be very much appreciated.

Wolfgang Haeuptli
  

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Re: compile-error: stdin is not a constant

[Daniel Jacobowitz]

On Wed, Nov 03, 1999 at 01:25:44PM +0100, Wolfgang Haeuptli wrote:
> 
> Hello people
> 
> sorry for the (probably) basic question...
> 
> Since I installed R5, some programs (that used to compile OK on R4) 
> complain about : 
> 
> initializer element for 'foo' is not constant
> 
> while compiling constructs like:
> 
> FILE *foo = stdin;   (or FILE *foo = {(FILE *) stdin};  )

Because it isn't a constant any more.

> 
> when I replaced this line with: FILE *foo = STDIN_FILENO; 
> ( defined in unistd.h), compilation works, but the resulting program
> segfaults...

Which should generate one hell of a warning, since STDIN_FILENO is a
small number, not a struct FILE *.

You need to initialize the variable early in main() or something along
those lines, or you can declare a constructor using __attribute__,
although I do not remember the syntax (search list archives).

Dan

/--------------------------------\  /--------------------------------\
|       Daniel Jacobowitz        |__|        SCS Class of 2002       |
|   Debian GNU/Linux Developer    __    Carnegie Mellon University   |
|         dan@debian.org         |  |       dmj+@andrew.cmu.edu      |
\--------------------------------/  \--------------------------------/

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Re: compile-error: stdin is not a constant

[Martin Costabel]

Daniel Jacobowitz wrote:
> 
> On Wed, Nov 03, 1999 at 01:25:44PM +0100, Wolfgang Haeuptli wrote:
> >
> > Hello people
> >
> > sorry for the (probably) basic question...
> >
> > Since I installed R5, some programs (that used to compile OK on R4)
> > complain about :
> >
> > initializer element for 'foo' is not constant
> >
> > while compiling constructs like:
> >
> > FILE *foo = stdin;   (or FILE *foo = {(FILE *) stdin};  )
> 
> Because it isn't a constant any more.
> 
> >
> > when I replaced this line with: FILE *foo = STDIN_FILENO;

Maybe this will work (1):

FILE *foo = (FILE *) STDIN_FILENO;

> > ( defined in unistd.h), compilation works, but the resulting program
> > segfaults...
> 
> Which should generate one hell of a warning, since STDIN_FILENO is a
> small number, not a struct FILE *.
> 
> You need to initialize the variable early in main() or something along
> those lines, or you can declare a constructor using __attribute__,
> although I do not remember the syntax (search list archives).

In a similar situation, I learned from Tom Rini that the correct way
would be (2)

static file *file ;
static void file_construct (void) __attribute__((constructor));
static void file_construct (void) { file = stdin; }

This might be in the list archives somewhere. I had a similar problem
with stdout when compiling Scilab. I used Tom's version (2), and it
worked, but I saw that the Scilab people in a later version used the
shorter version (1), and this seems to work, too. 

More precisely, they just added the "|| defined(__GNUC__)" in the
following code:

#if defined(__CYGWIN32__) || defined(__MINGW32__) || defined(__GNUC__)
static FILE *file= (FILE *) 0;
#define FPRINTF(x) ( file != (FILE*) 0) ?  fprintf x  : 0 
#else 
static FILE *file= stdout ;
#define FPRINTF(x) fprintf x  
#endif


--
Martin

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Re: compile-error: stdin is not a constant

[Daniel Jacobowitz]

On Wed, Nov 03, 1999 at 05:53:59PM +0000, Martin Costabel wrote:
> Maybe this will work (1):
> 
> FILE *foo = (FILE *) STDIN_FILENO;


No no no no no!  STDIN_FILENO is a -number-, not a -pointer-!

> In a similar situation, I learned from Tom Rini that the correct way
> would be (2)
> 
> static file *file ;
> static void file_construct (void) __attribute__((constructor));
> static void file_construct (void) { file = stdin; }

Yes, that's it.  gcc specific, but works.  (1) is DEFINITELY wrong.


Dan

/--------------------------------\  /--------------------------------\
|       Daniel Jacobowitz        |__|        SCS Class of 2002       |
|   Debian GNU/Linux Developer    __    Carnegie Mellon University   |
|         dan@debian.org         |  |       dmj+@andrew.cmu.edu      |
\--------------------------------/  \--------------------------------/

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