string-to-number

[Nick Roberts]

Currently string-to-number gives 0 for a non-number:

(string-to-number "a")^J
0

but 

(string-to-number "0")^J
0

gives the same result.  So what is a simple test for whether a string
represents a number or not?

If there isn't one,  how about:

(string-to-number "a")^J
nil

Of course this means an error is generated if you try to do arithmetic with a
non-number, but I think that this is appropriate and preferable to taking a
value of 0.


Nick


*** data.c      31 Oct 2005 00:56:53 +1300      1.256
--- data.c      17 Nov 2005 16:28:28 +1300      
***************
*** 2466,2472 ****
    register unsigned char *p;
    register int b;
    int sign = 1;
!   Lisp_Object val;
  
    CHECK_STRING (string);
  
--- 2466,2472 ----
    register unsigned char *p;
    register int b;
    int sign = 1;
!   Lisp_Object val = Qnil;
  
    CHECK_STRING (string);
  
***************
*** 2506,2514 ****
          if (digit < 0)
            break;
          v = v * b + digit;
        }
  
!       val = make_fixnum_or_float (sign * v);
      }
  
    return val;
--- 2506,2515 ----
          if (digit < 0)
            break;
          v = v * b + digit;
+         val = Qt;
        }
  
!       if (!NILP (val)) val = make_fixnum_or_float (sign * v);
      }
  
    return val;