The attached source (and compiler output) produces the "testBitset" executable,
which when run (no command line arguments) prints to std::cerr:
~/ootbc/common/test/src$ testBitset
p is: bitset<A>{a, c, e, g, k}
q is: bitset<A>{b:c, h, j:k}
r is: bitset<A>{a:c, e, g:h, j:k}
but (p|q) is: bitset<A>{d, f, h, j:k}
"bitset" is a class that is similar to std::bitset except that it has one bit
for each member of the enumeration that is a template argument to bitset. It is
built on top of std::bitset and all bitset operations ultimately reflect to
std::bitset.
Stream operator<< is overloaded to display bitsets as shown above. Bitset
defines operator| to produce a new bitset (of the same type) that is the
bitwise
"or" of the two arguments; this reflects ultimately to std::bitset::operator|=.
The test case "main" contains "bitset<A> r = (p|q);", where "p|q" produces a
temporary that is immediately used to initialize r. When printed out by
"std::cerr << r" this prints the correct value for the result of the "|"
operation.
However, if the "|" result is not stored into a variable but instead the
temporary is passed directly to the streaming operator<< by "std::cerr <<
(p|q)"
then the printed value is garbage. Exploration with the debugger shows that the
temporary is being overwritten. The temporary should live to the end of the
largest surrounding expression, which is the whole print statement, but it is
not.
--
Summary: Loses temporary in complex expression
Product: gcc
Version: 3.4.0
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: igodard at pacbell dot net
CC: gcc-bugs at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21672
