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Here, malloc() allocates space for a gadget and the cast immediately converts the returned pointer to a gadget *. This lets the compiler detect the invalid assignment, because it attempts to convert a gadget * into a widget *.
Compliant Solution
Repeating the same type in the sizeof expression and the pointer cast is easy to do, but still invites errors. Packaging the repetition in a macro, such as:
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Here, the entire allocation expression (to the right of the assignment operator) allocates storage for a widget and returns a widget *. If p were not a {{widget *, the compiler would complain about the assignment.
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When allocating an array with N elements of type T, the appropriate type in the cast expression is still T *, but the argument to malloc() should be of the form N * sizeof(T). Again, packaging this form as a macro, such as:
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