std::make_shared
| Defined in header
<memory>
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| template< class T, class... Args >
shared_ptr<T> make_shared( Args&&... args ); |
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Constructs an object of type T and wraps it in a std::shared_ptr using args as the parameter list for the constructor of T.
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[edit] Parameters
| args | - | list of arguments with which an instance of T will be constructed.
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[edit] Return value
std::shared_ptr of an instance of type T.
[edit] Exceptions
May throw std::bad_alloc or any exception thrown by the constructor of T. If an exception is thrown, this function has no effect.
[edit] Notes
This function is typically used to replace the construction std::shared_ptr<T>(new T(args...)) of a shared pointer from the raw pointer returned by a call to new. In contrast to that expression, std::make_shared<T> typically allocates memory for the T object and for the std::shared_ptr's control block with a single memory allocation (this is a non-binding requirement in the Standard), where std::shared_ptr<T>(new T(args...)) performs at least two memory allocations.
Moreover, code such as f(std::shared_ptr<int>(new int(42)), g()) can cause a memory leak if g throws an exception because g() may be called after new int(42) and before the constructor of shared_ptr<int>. This doesn't occur in f(std::make_shared<int>(42), g()), since two function calls are never interleaved.
[edit] Example
#include <iostream> #include <memory> void foo(const std::shared_ptr<int>& i) { (*i)++; } int main() { auto sp = std::make_shared<int>(12); foo(sp); std::cout << *sp << std::endl; }
Output:
13
[edit] See also
constructs new shared_ptr (public member function) |
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| creates a shared pointer that manages a new object allocated using an allocator (function template) |