The guarantees the standard gives you go like this:
1 == sizeof(char) <= sizeof(short) <= sizeof (int) <= sizeof(long) <= sizeof(long long)
So it's perfectly valid for sizeof (int) and sizeof (long) to be equal, and many platforms choose to go with this approach. You will find some platforms where int is 32 bits, long is 64 bits, and long long is 128 bits, but it seems very common for sizeof (long) to be 4.
(Note that long long is recognized in C from C99 onwards, but was normally implemented as an extension in C++ prior to C++11.)
