libstdc++/1897: basic_ostream operators contain non-ISO-standard variable length arrays.

[bumgard@roguewave.com]

>Number:         1897
>Category:       libstdc++
>Synopsis:       basic_ostream operators contain non-ISO-standard variable length arrays.
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Feb 06 18:06:01 PST 2001
>Closed-Date:
>Last-Modified:
>Originator:     Greg Bumgardner
>Release:        2.97 (2000-02-06)
>Organization:
>Environment:
N/A
>Description:
The operator implementations contained in bits/ostream.tcc 
contain numerous declarations of variable-length arrays.
The specific instances may be located by searching for the
variable "__pads".

Variable-length arrays are a GCC extension that violate the
ISO language standard.

This poses a problem for users who wish to compile their
code with -pedantic and -Werror.
>How-To-Repeat:
Instantiate basic_ostream<> operators while compiling with
-pedantic.
>Fix:
One possible fix is to replace the various variable-length 
array declarations with a dyanmic allocation (though this 
would open the code to problems with heap contention):

  _CharT __pads[...];  // NON-STANDARD

Replace with:

  auto_ptr<_CharT> __dyn(new _CharT[...]);
  _CharT* __pads = __dyn.get();

This will leave the rest of the code untouched, and yet will
insure that the storage is recovered at block exit.

The other alternative is to use the non-standard alloca()
funtion. Use of this function won't produce compiler 
warnings but may not be portable:

  _CharT __pads[...]; // NON-STANDARD

could be replaced with:

  _CharT* __pads = static_cast<_CharT*>(alloca(sizeof(_CharT)*length));

>Release-Note:
>Audit-Trail:
>Unformatted: