Why auto_ptr is deprecated in C++?

Why auto_ptr is deprecated in C++

TLDR; the auto_ptr smart pointer keyword has been deprecated in C++ 11 and removed in C++ 17.

Deprecation and Removal

• std::auto_ptr was deprecated in C++ 11.
• It was completely removed in C++ 17.

Why Was auto_ptr Deprecated?

• It had unsafe copy semantics.
• Copying an auto_ptr transferred ownership and left the source as nullptr.
• This behavior led to bugs, especially when used in STL containers or standard algorithms.

std::auto_ptr<int> p1(new int(42));
std::auto_ptr<int> p2 = p1; // Ownership transferred
std::cout << *p2 << std::endl; // OK
std::cout << *p1 << std::endl; // Undefined behavior (p1 is nullptr)

What to Use Instead

• std::unique_ptr — for exclusive ownership
• std::shared_ptr — for shared ownership

#include <memory>
#include <iostream>

int main() {
    std::unique_ptr<int> p1(new int(42));
    std::unique_ptr<int> p2 = std::move(p1); // Transfer ownership
    std::cout << *p2 << std::endl;
}

Comparison Table

Conclusion

Use std::unique_ptr or std::shared_ptr for modern C++ memory management. Avoid auto_ptr entirely in new codebases.

C/C++ Programming

• Understanding std::transform_reduce in Modern C++
• Implement a Lock Acquire and Release in C++
• Detecting Compile-time vs Runtime in C++: if consteval vs std::is_constant_evaluated()
• C++ Forward References: The Key to Perfect Forwarding
• Understanding dynamic_cast in C++: Safe Downcasting Explained
• C vs C++: Understanding the restrict Keyword and its Role in Optimization
• C++ Lvalue, Rvalue and Rvalue References
• C++ assert vs static_assert
• Why auto_ptr is Deprecated in C++?
• C++ What is the consteval? How is it different to const and constexpr?
• Tutorial on C++ std::move (Transfer Ownership)
• const vs constexpr in C++
• Tutorial on C++ Ranges
• Tutorial on C++ Smart Pointers
• Tutorial on C++ Future, Async and Promise
• The Memory Manager in C/C++: Heap vs Stack
• The String Memory Comparision Function memcmp() in C/C++
• Modern C++ Language Features
• Comparisions of push_back() and emplace_back() in C++ std::vector
• C++ Coding Reference: is_sorted_until() and is_sorted()
• C++ Coding Reference: iota() Setting Incrementing Values to Arrays or Vectors
• C++ Coding Reference: next_permutation() and prev_permutation()
• C++ Coding Reference: count() and count_if()
• C++ Code Reference: std::accumulate() and Examples
• C++ Coding Reference: sort() and stable_sort()
• The Next Permutation Algorithm in C++ std::next_permutation()

–EOF (The Ultimate Computing & Technology Blog) —