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[Bug libc/4342] scanf %lg problem with hex numbers


------- Additional Comments From jakub at redhat dot com  2007-04-23 13:44 -------
That's how *scanf initially worked, till the
1999-08-13  Ulrich Drepper  <drepper@cygnus.com>

        * stdio-common/tstscanf.c: Add test for hexadecimal float parsing
        problem.

        * stdio-common/vfscanf.c: Don't recognize hexadecimal floats without
        exponent.

--- stdio-common/vfscanf.c      21 Jun 1999 13:35:40 -0000      1.67
+++ stdio-common/vfscanf.c      13 Aug 1999 19:41:26 -0000      1.68
@@ -1410,8 +1410,8 @@ __vfscanf (FILE *s, const char *format, 

          /* Have we read any character?  If we try to read a number
             in hexadecimal notation and we have read only the `0x'
-            prefix this is an error.  */
-         if (wpsize == 0 || (is_hexa && wpsize == 2))
+            prefix or no exponent this is an error.  */
+         if (wpsize == 0 || (is_hexa && (wpsize == 2 || ! got_e)))
            conv_error ();

        scan_float:
--- stdio-common/tstscanf.c     6 Jun 1999 09:18:57 -0000       1.12
+++ stdio-common/tstscanf.c     13 Aug 1999 22:39:01 -0000      1.13
@@ -250,5 +250,20 @@ main (int argc, char **argv)
       }
   }
 
+  fputs ("Test 8:\n", stdout);
+  {
+    double d = 123456.789;
+    int res;
+
+    res = sscanf ("0x1234", "%lf", &d);
+    printf ("res = %d, d = %f\n", res, d);
+
+    if (res != 0 || d != 123456.789)
+      {
+       fputs ("test failed!\n", stdout);
+       result = 1;
+      }
+  }
+
   exit (result);
 }  

change.  My reading of both ISO C99 and current POSIX suggests that indeed
the exponent is only optional.  While ISO C99 has a footnote:
"fscanf pushes back at most one input character onto the input stream.
Therefore, some sequences that are acceptable to strtod, strtol, etc., are
unacceptable to fscanf." I don't think this applies here, as the hexadecimal
float exponent part is structured the same as decimal exponent part, just with
a different letter (p vs. e) and as the decimal float has the exponent part
optional, there is no reason why it couldn't be optional even for hexadecimal
floats.


-- 


http://sourceware.org/bugzilla/show_bug.cgi?id=4342

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