Re: libstdc++/3247

[Peter Schmid <schmid at snake dot iap dot physik dot tu-darmstadt dot de>]

The following reply was made to PR libstdc++/3247; it has been noted by GNATS.

From: Peter Schmid <schmid@snake.iap.physik.tu-darmstadt.de>
To: bkoz@gnu.org
Cc: gcc-gnats@gcc.gnu.org, gcc-bugs@gcc.gnu.org
Subject: Re: libstdc++/3247 
Date: Wed, 27 Jun 2001 03:55:23 +0200 (CEST)

 This is a known (IMHO mis-) "feature" of the slice or
 gslice interface of the ISO standard. This is because the C++ standard
 library does not specify that valarray subsets provide the same
 operations as valarrays. Therefore, some ugly casts to the valarray
 type are needed. Please confer page 554 of "The C++ Standard Library"
 by Josuttis. For example, the following code does indeed compile. To get a
 working program, you have to dimension the (val)arrays, though.
 
 Hope this helps,
 
 Peter Schmid
 
 Source code tbkoz.C
 #include <cstddef>
 #include <valarray>
 
 template <typename T1, typename Param1, class Param2> 
 void gnu_operator(T1, Param1 p1, Param2 p2)
 { std::operator*<T1>(p1, p2); }
 
 int main()
 {
     double dvar = 1.0;
     std::valarray<double> val_d;
     std::slice slc;
     std::gslice gslc;
     std::valarray<bool> val_b;
     std::valarray<std::size_t> val_sizet;
 
     gnu_operator(dvar, val_d, val_d);
     gnu_operator(dvar, val_d, static_cast<std::valarray<double> > (val_d[slc]));
     gnu_operator(dvar, val_d, static_cast<std::valarray<double> > (val_d[gslc]) ); 
     gnu_operator(dvar, val_d, static_cast<std::valarray<double> > (val_d[val_b]));
     gnu_operator(dvar, val_d, static_cast<std::valarray<double> > (val_d[val_sizet]));
 
         // and so on...
     gnu_operator(dvar, static_cast<std::valarray<double> > (val_d[slc]), static_cast<std::valarray<double> > (val_d[slc]));
 
     return 0;
 };
 
 Compiling tbkoz.C
 
 g++ -v tbkoz.C -W -Wall
 Reading specs from /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0/specs
 Configured with: ../gcc/configure --enable-shared --disable-nls --enable-threads=posix --enable-languages=c,c++,f77,objc
 Thread model: posix
 gcc version 3.0 20010615 (prerelease)
  /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0/cc1plus -v -D__GNUC__=3 -D__GNUC_MINOR__=0 -D__GNUC_PATCHLEVEL__=0 -D__ELF__ -Dunix -Dlinux -D__ELF__ -D__unix__ -D__linux__ -D__unix -D__linux -Asystem=posix -D__NO_INLINE__ -D__STDC_HOSTED__=1 -W -Wall -D_GNU_SOURCE -Acpu=i386 -Amachine=i386 -Di386 -D__i386 -D__i386__ -D__tune_i686__ -D__tune_pentiumpro__ tbkoz.C -D__GNUG__=3 -D__GXX_DEPRECATED -D__EXCEPTIONS -D__GXX_ABI_VERSION=100 -quiet -dumpbase tbkoz.C -W -Wall -version -o /tmp/cc6nIa8N.s
 GNU CPP version 3.0 20010615 (prerelease) (cpplib) (i386 Linux/ELF)
 GNU C++ version 3.0 20010615 (prerelease) (i686-pc-linux-gnu)
 	compiled by GNU C version 3.0 20010615 (prerelease).
 ignoring nonexistent directory "/usr/local/i686-pc-linux-gnu/include"
 #include "..." search starts here:
 #include <...> search starts here:
  /usr/local/include/g++-v3
  /usr/local/include/g++-v3/i686-pc-linux-gnu
  /usr/local/include/g++-v3/backward
  /usr/local/include
  /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0/include
  /usr/include
 End of search list.
  /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0/../../../../i686-pc-linux-gnu/bin/as -V -Qy -o /tmp/ccNiYQFr.o /tmp/cc6nIa8N.s
 GNU assembler version 2.11.90.0.15 (i686-pc-linux-gnu) using BFD version 2.11.90.0.15
  /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0/collect2 -m elf_i386 -dynamic-linker /lib/ld-linux.so.2 /usr/lib/crt1.o /usr/lib/crti.o /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0/crtbegin.o -L/usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0 -L/usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0/../../../../i686-pc-linux-gnu/lib -L/usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0/../../.. /tmp/ccNiYQFr.o -lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0/crtend.o /usr/lib/crtn.o