DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org C5D8D3851C22
MIME-Version: 1.0
Date: Sun, 18 Apr 2021 21:09:15 -0700
Message-ID: <CAAHpriMYTdJo5qFkN1y97wZVdx-ZkuggNrxHijiZdROwY_OEFg@mail.gmail.com>
Subject: sscanf doesn't handle hexadecimal floating-point input
To: cygwin@cygwin.com
From: Keith Thompson via Cygwin <cygwin@cygwin.com>
Reply-To: Keith Thompson <Keith.S.Thompson@gmail.com>
Cc: Keith Thompson <Keith.S.Thompson@gmail.com>
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Sender: "Cygwin" <cygwin-bounces@cygwin.com>

The *scanf() functions don't handle hexadecimal floating-point input
(for example "0x1p+0" representing 1.0).

A test program:

#include <stdio.h>
int main(void) {
    int ok = 1;
    float x = -1.0;
    int result = sscanf("0x1p+0", "%f", &x);
    const float expected_x = 1.0;
    const int expected_result = 1;
    printf("sscanf returned %d", result);
    if (result != expected_result) {
        ok = 0;
        printf(" (expected %d)", expected_result);
    }
    printf(", x = %g", x);
    if (x != expected_x) {
        ok = 0;
        printf(" (expected %g)", expected_x);
    }
    puts(ok ? ", PASSED" : ", FAILED");
}

On Cygwin, the output (compiled with gcc or clang) is:

sscanf returned 1, x = 0 (expected 1), FAILED

On Ubuntu, the output is:

sscanf returned 1, x = 1, PASSED

Looking through the newlib sources (git://sourceware.org/git/newlib-cygwin.git),
this might be related to the _WANT_IO_C99_FORMATS macro, but I haven't
looked into
the details.

The test case passes on Cygwin when compiled with i686-w64-mingw32-gcc
or x86_64-w64-mingw32-gcc.
--
Problem reports:      https://cygwin.com/problems.html
FAQ:                  https://cygwin.com/faq/
Documentation:        https://cygwin.com/docs.html
Unsubscribe info:     https://cygwin.com/ml/#unsubscribe-simple