error-new-delete-type-mismatch.md

title	description	ms.date	f1_keywords	helpviewer_keywords
Error: new-delete-type-mismatch	Source examples and live debug screenshots for new delete type mismatch errors.	03/02/2021	new-delete-type-mismatch	new-delete-type-mismatch error AddressSanitizer error new-delete-type-mismatch

Error: new-delete-type-mismatch

Address Sanitizer Error: Deallocation size different from allocation size

In this example, only ~Base, and not ~Derived, is called. The compiler generates a call to ~Base() because the Base destructor isn't virtual. When we call delete b, the object's destructor is bound to the default definition. The code deletes an empty base class (or 1 byte on Windows). A missing virtual keyword on the destructor declaration is a common C++ error when using inheritance.

Example - virtual destructor

// example1.cpp
// new-delete-type-mismatch error
#include <memory>
#include <vector>

struct T {
    T() : v(100) {}
    std::vector<int> v;
};

struct Base {};

struct Derived : public Base {
    T t;
};

int main() {
    Base *b = new Derived;

    delete b;  // Boom! 

    std::unique_ptr<Base> b1 = std::make_unique<Derived>();

    return 0;
}

Polymorphic base classes should declare virtual destructors. If a class has any virtual functions, it should have a virtual destructor.

To fix the example, add:

struct Base {
  virtual ~Base() = default;
}

To build and test this example, run these commands in a Visual Studio 2019 version 16.9 or later developer command prompt:

cl example1.cpp /fsanitize=address /Zi
devenv /debugexe example1.exe

Resulting error

:::image type="content" source="media/new-delete-type-mismatch-example-1.png" alt-text="Screenshot of debugger displaying new-delete-type-mismatch error in example 1.":::

See also

AddressSanitizer overview
AddressSanitizer known issues
AddressSanitizer build and language reference
AddressSanitizer runtime reference
AddressSanitizer shadow bytes
AddressSanitizer cloud or distributed testing
AddressSanitizer debugger integration
AddressSanitizer error examples