How do C/C++ compilers handle type casting between types with different value ranges?

Question

How do type casting happen without loss of data inside the compiler?

For example:

 int i = 10;
 UINT k = (UINT) k;

 float fl = 10.123;
 UINT  ufl =          


        

Answer 1

"Type" in C and C++ is a property assigned to variables when they're handled in the compiler. The property doesn't exist at runtime anymore, except for virtual functions/RTTI in C++.

The compiler uses the type of variables to determine a lot of things. For instance, in the assignment of a float to an int, it will know that it needs to convert. Both types are probably 32 bits, but with different meanings. It's likely that the CPU has an instruction, but otherwise the compiler would know to call a conversion function. I.e. & __stack[4] = float_to_int_bits(& __stack[0])

The conversion from char* to unsigned char* is even simpeler. That is just a different label. At bit level, p and up are identical. The compiler just needs to remember that *p requires sign-extension while *up does not.