GCC macro expansion arguments inside string

Question

I have a situation like this

#define PRE 0xF1

#define SR0 0B0000
#define SR1 0B0001
#define SR2 0B0010
#define SR3 0B0011

#define VIOTA(A0)  asm(".byte PRE, A0")

int main()
{
  VIOTA(SR1);
  return 0;
}

I have a top-level macro that expands out however the expansion contains more macros. These aren't being expanded and causing some problems.

The behaviour that I desire is that the end expansion is

asm(".byte 0xF1, 0B0000")

Here the inner macros have been expanded. I'm really not sure what I'm doing wrong at all. Any advice?

Answer 1

#define S(x) #x
#define SX(x) S(x)

#define VIOTA(A0) asm(".byte " SX(PRE) ", " SX(A0))

See details here: C Preprocessor, Stringify the result of a macro

Answer 2

Use the stringizing operator # to convert tokens into strings. However, since the stringizing operator can only be applied to macro parameters, you need to add some extra layers of macros:

#define PRE 0xF1

#define SR0 0B0000
#define SR1 0B0001
#define SR2 0B0010
#define SR3 0B0011

#define VIOTA(A0) VIOTA_HELPER1(PRE, A0)
#define VIOTA_HELPER1(PRE, A0) VIOTA_HELPER2(PRE, A0)
#define VIOTA_HELPER2(PRE, A0) asm(".byte" #PRE ", " #A0)

int main(void)
{
  VIOTA(SR1);
  return 0;
}

After preprocessing, this expands to this:

int main(void)
{
  asm(".byte " "0xF1" ", " "0B0001");
  return 0;
}

String constants get concatenated at compile time, so this is equivalent to asm(".byte 0xF1, 0B0001");.