Declaring Pascal-style strings in C

Question

In C, is there a good way to define length first, Pascal-style strings as constants, so they can be placed in ROM? (I\'m working with a small embedded system with a non-GCC

Answer 1

Here's my answer, complete with an append operation that uses alloca() for automatic storage.

#include 
#include 
#include 

struct pstr {
  unsigned length;
  char *cstr;
};

#define PSTR(x) ((struct pstr){sizeof x - 1, x})

struct pstr pstr_append (struct pstr out,
             const struct pstr a,
             const struct pstr b)
{
  memcpy(out.cstr, a.cstr, a.length); 
  memcpy(out.cstr + a.length, b.cstr, b.length + 1); 
  out.length = a.length + b.length;
  return out;
}

#define PSTR_APPEND(a,b) \
  pstr_append((struct pstr){0, alloca(a.length + b.length + 1)}, a, b)

int main()
{
  struct pstr a = PSTR("Hello, Pascal!");
  struct pstr b = PSTR("I didn't C you there.");

  struct pstr result = PSTR_APPEND(PSTR_APPEND(a, PSTR(" ")), b);

  printf("\"%s\" is %d chars long.\n", result.cstr, result.length);
  return 0;
} 

You could accomplish the same thing using c strings and strlen. Because both alloca and strlen prefer short strings I think that would make more sense.