Why Can\'t We Implicitly Convert a Pointer-to-Pointer to a Base Class in C ?

Implicit Conversion of Pointer-to-Pointer Between Derived and Base Classes

In C , the following code raises an error:

<code class="cpp">Child **cc = &c;
Base **bb = cc;</code>

The error message indicates that there is no implicit conversion from Child** to Base**. However, it is allowed to assign a child pointer to a base pointer:

<code class="cpp">Child *c = new Child();
Base *b = c;</code>

To understand why this difference exists, consider what would happen if the implicit conversion were allowed. One could then do the following:

<code class="cpp">*bb = new Base;</code>

This would result in c pointing to an instance of Base, which would violate the concept of derived and base classes. Therefore, C prohibits this implicit conversion.

To allow the assignment between Child** and Base**, one can use C-style casts or reinterpret_cast, but they sacrifice type safety. There is no way to achieve this conversion with an implicit cast or static_cast.

The above is the detailed content of Why Can\'t We Implicitly Convert a Pointer-to-Pointer to a Base Class in C ?. For more information, please follow other related articles on the PHP Chinese website!