unique_ptr&operator=(std::nullptr_t)noexcept; (3)(C++23 起为constexpr) unique_ptr&operator=(constunique_ptr&)=delete; (4) 1)移动赋值运算符。从r转移所有权到*this,如同在调用reset(r.release())后立即将std::forward<Deleter>(r.get_deleter())赋给get_deleter()。
=(std::function) Defined in header<functional> template<classR,class...ArgTypes> booloperator==(conststd::function<R(ArgTypes...)>&f, std::nullptr_t)noexcept; (1)(since C++11) template<classR,class...ArgTypes> booloperator==(std::nullptr_t,...
std::strong_ordering operator<=>( const std::shared_ptr<T>& lhs, const std::shared_ptr<U>& rhs ) noexcept; (7) (C++20 起)比较shared_ptr 与空指针 template< class T >bool operator==( const std::shared_ptr<T>& lhs, std::nullptr_t ) noexcept; (8) (C++11 起) ...
检查*this 是否占有对象,即是否有 get() != nullptr。 参数(无) 返回值若*this 占有对象则为 true,否则为 false。 示例运行此代码 #include <iostream> #include <memory> int main() { std::unique_ptr<int> ptr(new int(42)); if (ptr) std::cout << "重置前,ptr 为: " << *ptr << '\...
u.p is equal to nullptr, and if the pre-transfer u.d maintained state, such state has been transferred to u2.d. As in the case of a reset,u2 must properly dispose of its pre-transfer owned object via the pre-transfer associated deleter before the ownership transfer is considered complete...
basic_ostream& operator<<( std::nullptr_t ); (8) (C++17 起) basic_ostream& operator<<( std::basic_streambuf<CharT, Traits>* sb); (9) basic_ostream& operator<<( std::ios_base& (*func)(std::ios_base&) ); (10) basic_ostream& operator<<( std::basic_ios<CharT,Traits>&...
..) -> std::false_type; static constexpr bool value = decltype(test<T>(nullptr))::value; }; 上述代码定义了一个模板结构体has_equal_operator,它包含了两个静态成员函数test。第一个test函数使用了SFINAE(Substitution Failure Is Not An Error)技术,通过尝试调用"=="运算符来检查operator==是否存在。
/usr/lib/gcc/x86_64-pc-linux-gnu/5.4.0/include/g++-v5/bits/vector.tcc:167:5: note: no known conversion for argument 1 from ‘std::nullptr_t’ to ‘const std::vector<fftwf_plan_s*>&’ In file included from /usr/lib/gcc/x86_64-pc-linux-gnu/5.4.0/include/g++-v5/vector:64:0...
basic_ostream& operator<<( std::nullptr_t ); (10) (since C++17) basic_ostream& operator<<( short value ); (11) basic_ostream& operator<<( int value ); (12) basic_ostream& operator<<( unsigned short value ); (13) basic_ostream& operator<<( unsigned int value ); (14) ...
除了std::nothrow,C++还允许用户自定义分配器。如果自定义分配器在内存分配失败时返回空指针,那么new操作符也会返回空指针。 示例: #include <iostream> // 自定义分配器 void* operator new(std::size_t size) { static int counter = 0; counter++; if (counter > 1) { return nullptr; // 第二次调...