does the c preprocessor handle floating point math constants

问题

Say that I have

   #define A 23.9318;
   #define B 0.330043;
   #define C 5.220628;

I want to do

const unsigned result =  (unsigned)(0x01000000 * ( A * B / C ));    // unsigned is 32 bit

What I hope for is to have result with fixed decimal representation of the floating point calculations.

I cannot pre combine A,B,C together as their definition is not part of my code and I need it to work if they are changed.

回答1:

No, the standard C preprocessor operations do not perform floating-point arithmetic.

A C implementation is permitted, but not required, by the C standard to perform these operations at compile-time.

回答2:

This is not being offered as another answer, just an illustration that will not fit into the comments...

In a C99 compiler, with the following code, I get the following results (comments):

#include <ansi_c.h>

#define A 23.9318
#define B 0.330043
#define C 5.220628

#define result A*B/C  //1.512945007267325

const unsigned resultB = (unsigned)result*(0x01000000);

int main(void)
{
    resultB; //24394701

    return 0;
}  

So, although not required, some C implementations do include compile-time computations of floating point.

来源：https://stackoverflow.com/questions/21241031/does-the-c-preprocessor-handle-floating-point-math-constants