Annex C (informative) Compatibility [diff]

Change: It is now invalid to jump past a declaration with explicit or implicit initializer (except across entire block not entered).

Rationale: Constructors used in initializers may allocate resources which need to be de-allocated upon leaving the block.

Allowing jump past initializers would require complicated runtime determination of allocation.

Furthermore, many operations on such an uninitialized object have undefined behavior.

With this simple compile-time rule, C++ assures that if an initialized variable is in scope, then it has assuredly been initialized.

Effect on original feature: Deletion of semantically well-defined feature.

Difficulty of converting: Semantic transformation.

How widely used: Seldom.

Change: It is now invalid to return (explicitly or implicitly) from a function which is declared to return a value without actually returning a value.

Rationale: The caller and callee may assume fairly elaborate return-value mechanisms for the return of class objects.

If some flow paths execute a return without specifying any value, the implementation must embody many more complications.

Besides, promising to return a value of a given type, and then not returning such a value, has always been recognized to be a questionable practice, tolerated only because very-old C had no distinction between functions with void and int return types.

Effect on original feature: Deletion of semantically well-defined feature.

Difficulty of converting: Semantic transformation.

Add an appropriate return value to the source code, such as zero.

How widely used: Seldom.

For several years, many existing C implementations have produced warnings in this case.