RE: [Sdcc-user] libraries and global variables

[<MSoegtrop@Michael-Soegtrop.de>]

Dear Lawrence,

in ANSI-C and C++ "static" in front of a variable outside a function
simply meens NOT global. A function declared as static is only visible
inside of the compilation module (.c -file) in which it is defined. This
was different in K-R C, but this is obsolete now. This is a bit
non-obvious, but the language lawyers probably couldn't think of a
better keyword for this.

Best regards,

Michael

> -----Original Message-----
> From: sdc...@li...
> [mailto:sdc...@li...]On Behalf Of Lawrence
> Johnson
> Sent: Thursday, May 30, 2002 10:18 PM
> To: sdc...@li...
> Subject: [Sdcc-user] libraries and global variables
>
>
> This is possibly more of a programming question than an SDCC
> question,
> but I'm not sure, so I'll start here:
>
> With sdcc created libraries that use global variables, such
> as circular
> buffers for serial ports, presumably the variables must be declared
> global in the library source, or the source of one of the library
> functions.  These same variables must be declared as extern
> ... in every
> other place they're used, such as an application that may need access.
>
> I mentioned serial ports above because that's what I'm
> currently fiddling
> around with on an AT89C2051.  The serial port functions are based on
> those of Wolfgang Esslinger, as mentioned in the sdcc manual.
>  My first
> question, is that in looking into the contents of _ser.c,
> there is a bit
> variable:
>
> static bit ser_txBusy;
>
> This is declared outside of any function, hence it is global,
> I think.
> If this is the case, my question is: Why?
>
> I looked through some old programming documentation on
> storage classes
> and it isn't ever stated that you can't do this, but this may
> be because
> nobody would ever want to, unless there's a reason I don't see.
>
> When I was trying to link in functions from a library based
> on _ser.c, I
> kept getting this stubborn warning about ser_txBusy being declared as
> global and not being defined anywhere, even if I put the
> declaration as a
> global in my application (meaning right above main).  After a
> while, I
> started to question why this needs to be static, so I changed the
> declaration to simply read:
>
> bit ser_txBusy;
>
> ...and it now compiles, well sort of.  The next problem that cropped
> might be related to sdcc.
>
> The block of variables is as follows:
>
> unsigned char ser_txIndexIn;
> unsigned char ser_txIndexOut;
> unsigned char ser_rxIndexIn;
> unsigned char ser_rxIndexOut;
>
> unsigned char ser_txBuffer[TXBUF];
> unsigned char ser_rxBuffer[RXBUF];
>
> static bit ser_txBusy;
>
> What I did, initially, was create discrete functions one per
> file, with
> the file names identical to the functions.
>
> (John McClintock:  I was already well into this before you
> responded to
> my post of yesterday, so it was too late to turn back.)
>
> In each file, I declared the above block as:
>
> extern unsigned char ser_txIndexIn;
> extern unsigned char ser_txIndexOut;
> extern unsigned char ser_rxIndexIn;
> extern unsigned char ser_rxIndexOut;
>
> extern unsigned char ser_txBuffer[TXBUF];
> extern unsigned char ser_rxBuffer[RXBUF];
>
> extern static bit ser_txBusy;
>
> ...in all files except for ser_init.c, which obviously is the
> initialisation routine.  In that file, I declared without
> extern.  When I
> tried to then compile a program with only the initialisation
> routine and
> interrupt handler, I would get a "Multiple definition of
> _ser_rxBuffer"
> followed by a crash.  It strikes me as a little strange that
> it wouldn't
> complain about any of the other variables.  I checked and
> rechecked this
> because I couldn't see where the error was coming from.
> Eventually, I
> changed the above block of variables to all be extern in all
> functions
> and placed a global declaration in the header file for the would-be
> library.  The global declaration was wrapped within:
>
> #ifndef _SERLIB
> #define _SERLIB
> <global variables go here>
> #endif
>
> and the compile step had a -D_SERLIB on it for building the
> library.  I,
> of course, don't put the -D_SERLIB on the command-line for
> building the
> application, so the block gets declared there.
>
> Why didn't the global declaration in ser_init.c work?  Should it have
> worked at all?  This would have been much simpler in my
> books, and since
> you can't do anything without the initialisation step, you
> must end up
> declaring the global variables there, but not so.
>
>
>
> ______________________________________________________
> Lawrence Johnson                J-Tech Engineering Ltd
> 1050 Quadling Avenue   Coquitlam BC   Canada   V3K 2B2
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>
>
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