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The GNU C Library

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12.12.11 Example of Parsing a Template String

Here is an example of decoding argument types for a format string. We assume this is part of an interpreter which contains arguments of type NUMBER, CHAR, STRING and STRUCTURE (and perhaps others which are not valid here).

 
/* Test whether the nargs specified objects
   in the vector args are valid
   for the format string format:
   if so, return 1.
   If not, return 0 after printing an error message.  */

int
validate_args (char *format, int nargs, OBJECT *args)
{
  int *argtypes;
  int nwanted;

  /* Get the information about the arguments.
     Each conversion specification must be at least two characters
     long, so there cannot be more specifications than half the
     length of the string.  */

  argtypes = (int *) alloca (strlen (format) / 2 * sizeof (int));
  nwanted = parse_printf_format (string, nelts, argtypes);

  /* Check the number of arguments.  */
  if (nwanted > nargs)
    {
      error ("too few arguments (at least %d required)", nwanted);
      return 0;
    }

  /* Check the C type wanted for each argument
     and see if the object given is suitable.  */
  for (i = 0; i < nwanted; i++)
    {
      int wanted;

      if (argtypes[i] & PA_FLAG_PTR)
        wanted = STRUCTURE;
      else
        switch (argtypes[i] & ~PA_FLAG_MASK)
          {
          case PA_INT:
          case PA_FLOAT:
          case PA_DOUBLE:
            wanted = NUMBER;
            break;
          case PA_CHAR:
            wanted = CHAR;
            break;
          case PA_STRING:
            wanted = STRING;
            break;
          case PA_POINTER:
            wanted = STRUCTURE;
            break;
          }
      if (TYPE (args[i]) != wanted)
        {
          error ("type mismatch for arg number %d", i);
          return 0;
        }
    }
  return 1;
}


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