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Passing structs 2 ways
On the heap, on the stack

Jan.28

We look at the code of PassingStructs-heap.java, including:

• enum CatColor
• our unit tests (using just assert, not JUnit)
• boilerplate constructor, toString
• Cat.equals
• use of float literals (suffix f)

Then, draw the memory diagram of how things look at the time we call scratch().

Finally, compare Java version with a corresponding C version: passingStructs-heap.c.

Note how the helper function can't change local vars: in particular, one of the local vars was the pointer-to-heap, and that pointer is not changed — it still points to the same place it did before. However, the contents sitting over at the pointed-to location might change, and that can be seen/used by the calling function.

Jan.30

We review/finish the above points, reminding ourselves of the memory diagram.

Unlike Java, we can also create structs directly on the stack; they are also passed by copying bits (just like all parameters we've seen, including object-references in Java and C).

pass-structs-by-value.c: Review the code, and draw its different-looking memory diagram.

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