C++ .release()

In C++, the .release() function is a member of the smart pointer class std::unique_ptr. It releases ownership of the managed object and returns a raw pointer to that object. After calling .release(), the unique_ptr becomes empty and holds nullptr.

Syntax

If ptr is a std::unique_ptr, then:

ptr.release();

Parameters:

The function takes no parameters.

Return value:

Returns the raw pointer to the object managed by the unique_ptr before the call.

Example

This example demonstrates how to use .release():

#include <iostream>
#include <memory>

int main() {
  // Create a unique_ptr managing a new int
  std::unique_ptr<int> auto_pointer(new int);

  // Assign value 10 to the managed object
  *auto_pointer = 10;

  // Release ownership and get the raw pointer
  int* manual_pointer = auto_pointer.release();

  // Output the value pointed to by manual_pointer
  std::cout << "manual_pointer now points to " << *manual_pointer << "\n";

  // Manually delete the raw pointer to avoid memory leak
  delete manual_pointer;

  return 0;
}

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The output of this code is:

manual_pointer now points to 10

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This code creates a unique_ptr managing an integer with value 10. Calling .release() transfers ownership to manual_pointer, and the raw pointer must be manually deleted to prevent a memory leak.

Codebyte Example

In this codebyte example, std::unique_ptr is used to manage a FILE*. When there is a need to pass the file pointer to a legacy C-style API that expects a raw FILE*, .release() is used to transfer ownership safely:

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