On Linux sscanf, vsscanf, fscanf and sscanf_s hand their conversions to
glibc. Since glibc 2.38, code built as GNU C++ calls the C23 entry
points (__isoc23_vsscanf, __isoc23_vfscanf, __isoc23_sscanf), whose %i
reads a 0b/0B binary prefix. On main,
sscanf("0b101 x", "%i%n%7s", &value, &end, rest) stores value 5 and
end 5 and leaves "x" for the %s; " -0B11" gives -3. TechnicalDebt
records this.
FreeBSD's %i knows only the 0 and 0x prefixes. FreeBSD 11.4
lib/libc/stdio/vfscanf.c, parseint, lines 345-353 and 371-380:
case '0':
if (base == 0) {
base = 8;
flags |= PFXOK;
}
...
/* letters ok iff hex */
case 'A': case 'B': case 'C':
case 'D': case 'E': case 'F':
case 'a': case 'b': case 'c':
case 'd': case 'e': case 'f':
/* no need to fix base here */
if (base <= 10)
break; /* not legal here */
so "0b101" stores 0, consumes the "0" and leaves "b101", as C17 does
and as the strtol family here already does.
With glibc the scanf family now calls __isoc99_vsscanf and
__isoc99_vfscanf, the entry points GNU C++ used before glibc 2.38
(exported since 2.7), which read %i without the binary prefix. Other
hosts keep std::vsscanf and std::vfscanf. The TechnicalDebt entry is
removed.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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