When copy elision occurs, the implementation treats the source and target of the omitted initialization as simply two different ways of referring to the same object. The destruction occurs at the later of the times when the two objects would have been destroyed without the optimization. ...
__cpp_guaranteed_copy_elision201606L(C++17)通过简化的值类别提供有保证的复制消除 示例 运行此代码 #include <iostream>structNoisy{Noisy(){std::cout<<"在 "<<this<<" 构造"<<'\n';}Noisy(constNoisy&){std::cout<<"复制构造\n";}Noisy(Noisy&&){std::cout<<"移动构造\n";}~Noisy(){std::...
这里现代 C++ 编译器有一个牛逼的优化,叫做copy elision. 在一个声明了 value 参数的函数中,当函数实际参数 是rvalue 时,编译器能判断出多余的 copy 操作,并主动忽略之,则在函数内直接使用了实参对象。这样的做法和 const ref 似乎是一致的。其实 Return Value Optimization 也是 copy elision 的一个体现。那么...
(201606L, __cpp_guaranteed_copy_elision) COMPILER_FEATURE_ENTRY(201603L, __cpp_hex_float) COMPILER_FEATURE_ENTRY(201606L, __cpp_if_constexpr) COMPILER_FEATURE_ENTRY(201606L, __cpp_inline_variables) COMPILER_FEATURE_ENTRY(201411L, __cpp_namespace_attributes) COMPILER_FEATURE_ENTRY(201510...
[3] https://en.cppreference.com/w/cpp/memory/shared_ptr/get[4] https://en.cppreference.com/w/cpp/language/copy_elision[5] https://www.boost.org/doc/libs/1_76_0/libs/rational/[6] https://www.boost.org/doc/libs/1_76_0/libs/utility/operators.htm...
DR11: Guaranteed copy elision for piecewise construction P0475R1 9 Yes 19.29 (16.10)* Yes std::bit_cast() (FTM)* P0476R2 11 14 19.27* 14.0.3* Integral power-of-2 operations: std::bit_ceil(), std::bit_floor(), std::bit_width(), std::has_single_bit() (FTM)* P0556R3P...
Guaranteed copy elision (FTM)* P0135R1 7 4 19.13* Yes 5.0 19.0.1 19.1 11.0 11.0 10.3 17.1.0 Replacement of class objects containing reference members P0137R1 7 6 19.14* Yes 5.0 19.1 11.0 11.0 10.3 17.1.0 Stricter expression evaluation order P0145R3 7 4 19.14* Yes 5.0 19.0.1 19.1...
Returning by value may involve construction and copy/move of a temporary object, unlesscopy elisionis used. Specifically, the conditions for copy/move are as follows: Automatic move from local variables and parameters Theexpressionismove-eligibleif it is a (possibly parenthesized)identifier expression...
In addition, the implicit conversion in copy-initialization must produceTdirectly from the initializer, while, e.g. direct-initialization expects an implicit conversion from the initializer to an argument ofT's constructor. structS{S(std::string){}};// implicitly convertible from std::stringS s(...
CWG 2268C++11copy/move of a union with a mutable member was prohibited by the resolution ofCWG issue 2004allowed if the object is created within the constant expression CWG 2278C++98the resolution ofCWG issue 2022was not implementableassume that copy elision is never ...