I am observing some strange behavior that I can't quite explain myself. The code looks like this:
#include <memory>
#include <vector>
#include <algorithm>
int main(){
std::vector<double> t1(10, 5.0);
std::vector<double*> t2(10);
std::transform(t1.begin(), t1.end(), t2.begin(), std::addressof<double>);
//std::transform(t1.begin(), t1.end(), t2.begin(), [](double& a){return &a;});
}
And here is a version to play around with https://godbolt.org/g/YcNdbf The problem is that this code compiles fine using gcc4.9-6.3 but fails under gcc 7.1. Clang doesn't like it either.
(edit) Error messages from gcc 7.1:
<source>: In function 'int main()':
8 : <source>:8:76: error: no matching function for call to 'transform(std::vector<double>::iterator, std::vector<double>::iterator, std::vector<double*>::iterator, <unresolved overloaded function type>)'
std::transform(t1.begin(), t1.end(), t2.begin(), std::addressof<double>);
^
In file included from /opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/algorithm:62:0,
from <source>:3:
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/stl_algo.h:4281:5: note: candidate: template<class _IIter, class _OIter, class _UnaryOperation> _OIter std::transform(_IIter, _IIter, _OIter, _UnaryOperation)
transform(_InputIterator __first, _InputIterator __last,
^~~~~~~~~
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/stl_algo.h:4281:5: note: template argument deduction/substitution failed:
8 : <source>:8:76: note: could not resolve address from overloaded function 'addressof<double>'
std::transform(t1.begin(), t1.end(), t2.begin(), std::addressof<double>);
^
In file included from /opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/algorithm:62:0,
from <source>:3:
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/stl_algo.h:4318:5: note: candidate: template<class _IIter1, class _IIter2, class _OIter, class _BinaryOperation> _OIter std::transform(_IIter1, _IIter1, _IIter2, _OIter, _BinaryOperation)
transform(_InputIterator1 __first1, _InputIterator1 __last1,
^~~~~~~~~
/opt/compiler-explorer/gcc-7.1.0/include/c++/7.1.0/bits/stl_algo.h:4318:5: note: template argument deduction/substitution failed:
8 : <source>:8:76: note: could not resolve address from overloaded function 'addressof<double>'
std::transform(t1.begin(), t1.end(), t2.begin(), std::addressof<double>);
^
Compiler exited with result code 1
However, I can't quite figure out why it is not working.
Thanks in advance to anyone trying to help :)
To avoid accidentally taking the address of temporaries, the library has gotten a second (deleted) signature for addressof
:
template <class T> constexpr T* addressof(T& r) noexcept;
template <class T> const T* addressof(const T&& elem) = delete;
See http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2598
So now the compiler doesn't know if your code should match the deleted function or not...