c++ - Conversion between numeric types of the same kind

Question

I was reading http://www.cplusplus.com/doc/tutorial/typecasting/. It says that:

• Otherwise, if the conversion is between numeric types of the same kind (integer-to-integer or floating-to-floating), the conversion is valid, but the value is implementation-specific (and may not be portable).

But I really didn't understand what does the above quote mean to say? Will someone please explain it using an simple example? Why conversion between numeric type of same kind results in implementation-specific value? What is the reason?

Answer 1

Let's consider the following example:

    long long int lli = 5000000000;
    long int li;
    int i;
    li = lli;
    i = li;

Can you predict the values of lli, li and i? Or whether li and i have the same value?

Answer is - values depend on the number of bytes allocated for each type! I.e. for some cases int is equal to long int, for others long int is equal to long long int, but in general longer types just CAN be longer. Similar (in sense of memory size) for float, double and long double.