Return value optimization and copy elision in C
c++,c,struct,return-value-optimization,copy-elision
RVO/NRVO are clearly allowed under the "as-if" rule in C. In C++ you can get observable side-effects because you've overloaded the constructor, destructor, and/or assignment operator to give those side effects (e.g., print something out when one of those operations happens), but in C you don't have any ability to...
Too many destructors called on template classes (N)RVO optimization
c++,templates,c++11,copy-elision
(N)RVO can never introduce a discrepancy between the number of constructor and destructor calls. It's designed to make that principally impossible. The problem is with your code. According to the rules of the language, a constructor template is never used to produce a copy constructor. The copy constructor is never...
Copy elision in range based for loops
Quite simply because there is no rule to allow copy elision in this case. It's generally only allowed when returning a value from a function, or when copy-initialising. In every other case, where a copy has side-effects (such as your I/O), copy elision is prohibited. It would be madness for...
Auto and copy elision
I guess you use libstdc++. It is currently not standard conformant in this regard, i.e. the iostreams do not have move constructors yet although they should have. It will be fixed in version 5: Runtime Library (libstdc++) ... Full support for C++11, including the following new features: ... movable and...
Template class copy constructor not called
c++,templates,copy-constructor,copy-elision
This is what is known as Copy Elision. It's a nice optimization where a copy clearly isn't necessary. Instead of effectively running the code: SmartPtr<int> __tmp(new int); SmartPtr<int> ptr4(__tmp); __tmp.~SmartPtr<int>(); The compiler can know that __tmp only exists to construct ptr4, and thus is allowed to construct __tmp in-place in...
Do RVO and copy elision only work within one compilation unit or not?
Normally, yes, but in principle, using Link-Time-Optimization (-flto for GCC/Clang compilers and linkers) or Link-Time-Code-Generation (/LTCG and /GL for MSVC's compiler and linker), the compiler and linker can leverage their shared knowledge and perhaps inline code and elide copies. GCC's manual states: [...] this causes all the interprocedural analyses and...
copy elision visible side effect
The whole point of singling copy elision out as a on optimization in specific cases is to allow eliding side effects of copy construction. That is, yes, it expected that copy elision happens despite the copy constructor and/or the destructor having side effects. If you don't want copy elision to...
Copy Elision Misunderstanding
Yes your understanding is right. Your line of code (without copy eliding) is similar to int main() { { A temp = func1(); // 2nd copy func2(temp); // 3rd copy } } ...
Return object that cannot be copied by value
c++,copy-constructor,c++14,copy-elision
This one is wrong: Object&& loadFromFile(const std::string& name) { Object obj; ... return std::move(obj); } You are returning a reference to a local variable, and this is undefined behaviour. The object dies and what you return is a reference to your nose, so demons can come out of it. The...