flac dev - Sep 2007 - Two GCC warnings flags you should enable ASAP

Josh,

There are two GCC warning flags you should enable for all the 
C code ASAP. From the gcc man page:

  -Wmissing-prototypes (C only)
    Warn if a global function is defined without a previous prototype
    declaration.  This warning is issued even if the definition itself 
    provides a prototype.  The aim is to detect global functions that 
    fail to be declared in header files.

  -Wstrict-prototypes (C only)
    Warn if a function is declared or defined without specifying the 
    argument types.  (An old-style function definition is permitted 
    without a warning if preceded by a declaration which specifies the
    argument types.)

Currently in the file src/share/utf8/charset.c you use the new allocation
functions without including "include/share/alloc.h". The first warning
flag above would catch this issue. The second warning flag will catch
things like old-style K&R function definitions which were obsoleted
by the 18 year old 1989 C standard :-).

These two warning flags have been available at least since gcc-2.95.
All the 3 and 4 series gcc compilers accept them.

Cheers,
Erik
-- 
-----------------------------------------------------------------
Erik de Castro Lopo
-----------------------------------------------------------------
"When exported to Muslim lands, various aspects of Western pop
culture must be modified in order to accommodate Muslim sensibilities.
When Muslims come West, various aspects of Western pop culture must
be modified in order to accommodate Muslim sensibilities."
-- http://www.jihadwatch.org/dhimmiwatch/archives/008623.php

Erik de Castro Lopo wrote:
> There are two GCC warning flags you should enable for all the 
> C code ASAP.
Sorry, I don't want to seem too pushy on this issue, but I consider
-Wmissing-prototypes a really important issue. It bit me really
badly once and has been a hobby horse of mine ever since.

The reason its important is that in C (C++ is a different matter
which I'll explain later), if no prototype for a function is seen,
the compiler assumes that the caller will get the number, order
and type of the function arguments correct. However, if the caller
gets it wrong (or the function definition changes) really bad stuff
happens (ie really horrible, hard to track down bugs). In addition,
if you don't include the header, automake doesn't realise that the
caller depends on the header (and hence the function definition).

In C++ its a different matter. Because of function overloading, the
C++ linker does the checking of function arguments, order and count
and doesn't allow you to mess up. Thats why the -Wmissing-prototype
flag is C only.

Hope this helps.

Cheers,
Erik
-- 
-----------------------------------------------------------------
Erik de Castro Lopo
-----------------------------------------------------------------
"I don't think any MS Exec will ever die of old age. Satan
doesn't need the competition."
-- Digital Wokan on LinuxToday.com

Erik de Castro Lopo wrote:
> Sorry, I don't want to seem too pushy on this issue, but I consider
> -Wmissing-prototypes a really important issue. It bit me really
> badly once and has been a hobby horse of mine ever since.
I've done some more investigation of this issue. It turns out
that the dangerous scenario I outline in my previous email is
actually caught by the -Wall flag which you already use.

The -Wmissing-prototype warning flag catches a related (and even more
subtle) problem which the -Wall and -W/-Wextra flags ignore.

Consider three files:

      first.c
      second.c
      second.h

The file first.c includes second.h which defines function X, with the
implementation of function X being in second.c. Now consider the case
where second.c does not include second.h and the implementation in
second.c does not match the prototype in second.h. In this case, first.c
which includes second.h expects function X to behave as it was specified
in the header, but the implementation in second.c doesn't match.

This is a recipie for pain very similar to what I describe in my previous
email. However, like the previous problem, the C++ linker would catch the
mis-match.

Erik
-- 
-----------------------------------------------------------------
Erik de Castro Lopo
-----------------------------------------------------------------
"The X-files is too optimistic. The truth is not out there."
-- Anthony Ord

I'll add these, I think they didn't get in with your previous patch
because I withheld a part of it for some other reason...

--- Erik de Castro Lopo <erikd-flac@mega-nerd.com> wrote:
> Josh,
> 
> There are two GCC warning flags you should enable for all the 
> C code ASAP. From the gcc man page:
> 
>   -Wmissing-prototypes (C only)
>     Warn if a global function is defined without a previous prototype
>     declaration.  This warning is issued even if the definition
> itself 
>     provides a prototype.  The aim is to detect global functions that
> 
>     fail to be declared in header files.
> 
>   -Wstrict-prototypes (C only)
>     Warn if a function is declared or defined without specifying the 
>     argument types.  (An old-style function definition is permitted 
>     without a warning if preceded by a declaration which specifies
> the
>     argument types.)
> 
> Currently in the file src/share/utf8/charset.c you use the new
> allocation
> functions without including "include/share/alloc.h". The first
> warning
> flag above would catch this issue. The second warning flag will catch
> things like old-style K&R function definitions which were obsoleted
> by the 18 year old 1989 C standard :-).
> 
> These two warning flags have been available at least since gcc-2.95.
> All the 3 and 4 series gcc compilers accept them.
> 
> Cheers,
> Erik
> -- 
> -----------------------------------------------------------------
> Erik de Castro Lopo
> -----------------------------------------------------------------
> "When exported to Muslim lands, various aspects of Western pop
> culture must be modified in order to accommodate Muslim
> sensibilities.
> When Muslims come West, various aspects of Western pop culture must
> be modified in order to accommodate Muslim sensibilities."
> -- http://www.jihadwatch.org/dhimmiwatch/archives/008623.php
> _______________________________________________
> Flac-dev mailing list
> Flac-dev@xiph.org
> http://lists.xiph.org/mailman/listinfo/flac-dev
> 


       
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