you can convert a short to an int without casting and it will roundtrip without loss of data; similarly you can roundtrip any data pointer through a void pointer without loss of data. It doesn't mean that an int has the same representation of a short or a void* has (necessarily) the same representation as any other pointer.
In C++ any pointer is also implicitly convertible to a void *, it is the reverse implicit conversion that is prohibited as it is not safe in the general case.
For consistency C++ should also prohibit implicit narrowing conversions (e.g. int to short ); I guess this was thought to break too much existing code and it is generally safer than a pointer conversion (although potentially lossy the behavior is fully defined). Many compilers will warn about it, and narrowing conversions are now prohibited in braced initialization.
Comments
you can convert a short to an int without casting and it will roundtrip without loss of data; similarly you can roundtrip any data pointer through a void pointer without loss of data. It doesn't mean that an int has the same representation of a short or a void* has (necessarily) the same representation as any other pointer.
In C++ any pointer is also implicitly convertible to a void *, it is the reverse implicit conversion that is prohibited as it is not safe in the general case.
For consistency C++ should also prohibit implicit narrowing conversions (e.g. int to short ); I guess this was thought to break too much existing code and it is generally safer than a pointer conversion (although potentially lossy the behavior is fully defined). Many compilers will warn about it, and narrowing conversions are now prohibited in braced initialization.
Re implicit narrowing conversions, I think most compilers have warnings for this by now both in C and C++, at least in the higher warning levels.