What do the asterisks in this C language macro do?

#define asreal(x) (*((float *) &x))

I know about pointers in C, but it seems like the asterisks in this macro are being used for arithmetic? I am not sure exactly what is happening here.

Is the &x bitwise result being cast to a float pointer? Then why is there an additional asterisk outside of that expression?

CodePudding user response：

&x - take address of x

(float*) &x - cast it to float*

*((float *) &x) dereference casted result (result type is float)

(*((float *) &x)) - wrap it in paranthesis so it doesn't interfere with outside code

So basically, the code takes bytes in x and reinterprets them as float. Note that this macro would only be useful if

• x is a float already or
• if it contains binary data equal to a valid float.

It cannot be used to convert int value to float (unless you try to use the bit representation of that int, not the value) It will also break if called like asreal(x y) or in quite a lot of other possiblities. I'm also not sure if it's defined behaviour in C, but if you are trying to "understand the machine", you are probably ready for certain UBs.