https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122224
Bug ID: 122224
Summary: std::prev when called with non-bidirectional iterators
Product: gcc
Version: 15.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: terra at gnome dot org
Target Milestone: ---
Created attachment 62525
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=62525&action=edit
Preprocessed source
Calling std::prev on a iterator that isn't bidirectional is wrong.
Should this compile? (See also bug 122194.)
Bug 62039 is similar, but claimed fixed ages ago.
For me, it compiles. Without -O, it asserts. With -O, I get an infinite loop.
The former is better than the latter but a compile error would be better.
$ cat ttt.C
#include <iostream>
#include <sstream>
#include <iterator>
int
main(int, char **)
{
std::istringstream str { "Howdy!" };
auto it = std::istream_iterator<char>(str);
auto it2 = std::next(it);
auto it3 = std::prev(it2);
return 0;
}
$ g++ -std=gnu++23 ttt.C
$ ./a.out
/usr/local/products/gcc/15.1.0/include/c++/15.1.0/bits/stl_iterator_base_funcs.h:163:
constexpr void std::__advance(_InputIterator&, _Distance, input_iterator_tag)
[with _InputIterator = istream_iterator<char>; _Distance = long int]: Assertion
'__n >= 0' failed.
Aborted (core dumped)
$ g++ -std=gnu++23 -O ttt.C
$ ./a.out
^C
$ g++ -v
Using built-in specs.
COLLECT_GCC=/usr/local/products/gcc/15.1.0/bin/g++
COLLECT_LTO_WRAPPER=/usr/local/products/gcc/15.1.0/lib/gcc/x86_64-suse-linux/15.1.0/lto-wrapper
Target: x86_64-suse-linux
Configured with: ../../gcc-15.1.0/configure
--enable-languages=c,c++,fortran,jit --enable-host-shared --with-pic
--enable-targets=x86_64-suse-linux,i686-suse-linux
--prefix=/usr/local/products/gcc/15.1.0 --with-gnu-as
--with-as=/usr/local/products/gcc/binutils-2.44/bin/as
--with-ld=/usr/local/products/gcc/binutils-2.44/bin/ld.gold --enable-link-mutex
--enable-gnu-indirect-functions --enable-linux-futex --enable-threads=posix
--enable-shared --enable-__cxa_atexit --enable-libstdcxx-allocator=new
x86_64-suse-linux --enable-libstdcxx-backtrace=yes --with-zstd
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 15.1.0 (GCC)
