auto_ptr is a class template that was available in previous versions of the C++ Standard Library (declared in the header file), which provides some basic RAII features for C++ raw pointers. It has been replaced by the unique_ptr class.
The auto_ptr template class describes an object that stores a pointer to a single allocated object that ensures that the object to which it points gets destroyed automatically when control leaves a scope.[1]
The C++11 standard made auto_ptr deprecated, replacing it with the unique_ptr class template.[2][3]auto_ptr was fully removed in C++17.[4]
For shared ownership, the shared_ptr template class can be used. shared_ptr was defined in C++11 and is available in the Boost library.[5]
Declaration
The auto_ptr class is declared in ISO/IEC 14882, section 20.4.5 as:
namespace std {
template class auto_ptr { public: typedef X element_type;
The auto_ptr has semantics of strict ownership, meaning that the auto_ptr instance is the sole entity responsible for the object's lifetime. If an auto_ptr is copied, the source loses the reference. For example:
include
include
using namespace std;
int main(int argc, char **argv)
{
int *i = new int; auto_ptr x(i); auto_ptr y; y = x; cout << x.get() << endl; // Print NULL cout << y.get() << endl; // Print non-NULL address i
}
This code will print a NULL address for the first auto_ptr object and some non-NULL address for the second, showing that the source object lost the reference during the assignment (=). The raw pointer i in the example should not be deleted, as it will be deleted by the auto_ptr that owns the reference. In fact, new int could be passed directly into x, eliminating the need for i.
Notice that the object pointed by an auto_ptr is destroyed using operator delete; this means that you should only use auto_ptr for pointers obtained with operator new. This excludes pointers returned by malloc/calloc/realloc, and pointers to arrays (because arrays are allocated by operator new[] and must be deallocated by operator delete[]).
Because of its copy semantics, auto_ptr may not be used in STL containers that may perform element copies in their operations.
See also
Smart pointer
Generic programming
References
1. ^{{cite web |url=http://msdn2.microsoft.com/en-us/library/ew3fk483.aspx |publisher=Microsoft |title=auto_ptr Class |accessdate=2006-09-27}} 2. ^{{cite web|title=Working Draft, Standard for Programming Language C++ N3242|url=http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3242.pdf|accessdate=2013-02-17|page=1233|date=28 February 2011}} 3. ^{{cite web|last=Kalev|first=Danny|title=Using unique_ptr, Part I|url=http://www.informit.com/guides/content.aspx?g=cplusplus&seqNum=400|publisher=informIT|accessdate=30 September 2010}} 4. ^{{cite web|title=Programming Language C++, Library Evolution Working Group JTC1/SC22/WG21 N4190|url=http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4190.htm|accessdate=2016-08-29|date=2014-10-09}} 5. ^{{cite web |url=http://www.ddj.com/dept/cpp/184401839 |publisher=Dr. Dobb's |title=Collecting Shared Objects |date=2004-07-01 |accessdate=2006-09-27}}
External links
Using auto_ptr effectively
Avoiding Memory Leaks with auto_ptr
Article "[https://web.archive.org/web/20080306193914/http://gethelp.devx.com/techtips/cpp_pro/10min/10min1199.asp Using the auto_ptr Class Template to Facilitate Dynamic Memory Management]" by Danny Kalev
Article "Container of auto_ptr" by Zeeshan Amjad
Article "Update on auto_ptr" by Scott Meyers
[https://gcc.gnu.org/onlinedocs/libstdc++/libstdc++-html-USERS-4.0/classstd_1_1auto__ptr.html auto_ptr Class Template Reference from GNU libstdc++]
auto_ptr reference from Rogue Wave
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