| Summary: | std::min std::max and RValue | ||
|---|---|---|---|
| Product: | gcc | Reporter: | Lisp2D <lisp2d> |
| Component: | c++ | Assignee: | Not yet assigned to anyone <unassigned> |
| Status: | RESOLVED DUPLICATE | ||
| Severity: | normal | CC: | daniel.kruegler |
| Priority: | P3 | ||
| Version: | 4.8.1 | ||
| Target Milestone: | --- | ||
| Host: | Target: | ||
| Build: | Known to work: | ||
| Known to fail: | Last reconfirmed: | ||
Yes, that's required by the standard, nothing we can do about it. Issue a warning would not hurt. Likely error in the standard. The right set of functions must return a copy of the data and return a the temporary link with real data.
Working version of it:
size_t const & min2(size_t const & x,size_t const & y){
return std::min(x,y);}
size_t min2(size_t const && x,size_t const & y){
return {std::min(x,y)};}
size_t min2(size_t const & x,size_t const && y){
return {std::min(x,y)};}
May be do like this?
Feel free to post a message on https://groups.google.com/a/isocpp.org/forum/#!forum/std-proposals to suggest this. https://isocpp.org/std gives information on making official proposals. In gcc we only implement what the standard tells us. (In reply to Marc Glisse from comment #5) > Feel free to post a message on > https://groups.google.com/a/isocpp.org/forum/#!forum/std-proposals to > suggest this. https://isocpp.org/std gives information on making official > proposals. In gcc we only implement what the standard tells us. It is off-topic here, but Howard's similar proposal had been rejected: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2199.html Well yes, that is now 7 years ago... Linking to the diagnostic issue. *** This bug has been marked as a duplicate of bug 60517 *** If I mark f as static or inline (so the optimizer changes f to take its argument by value), I get with g++-5:
w2.c: In function 'int main()':
w2.c:11:7: warning: '<anonymous>' is used uninitialized in this function [-Wuninitialized]
f(i);
^
w2.c:13:7: warning: '<anonymous>' is used uninitialized in this function [-Wuninitialized]
f(a);
^
(not the best error message, but a good first step)
It is quite fragile though, if instead f is inlined (rename main to help convince the optimizer), we end up with:
_49 = std::basic_ostream<char>::_M_insert<long unsigned int> (&cout, _9(D));
and don't warn about it (I didn't check, but I assume _9 is marked TREE_NO_WARNING).
|
Declaring reference of result of functions MIN or MAX we get a DEAD memory when one of arguments is an RValue. // gcc -std=c++11 -Os bug.cpp // gcc -std=c++11 -O2 bug.cpp #include<iostream> void f(size_t const & x){ std::cout << "f:x=" << x << std::endl;} int main(void){ size_t x{1}; size_t y{2}; size_t z{4}; size_t const & i=std::min(z,x + y); f(i); size_t const & a=std::max(x,y + z); f(a);}