[musl] swprintf: minimum width ignored for %lc

[musl] swprintf: minimum width ignored for %lc

[Bruno Haible]

On musl-1.2.3 I see this violation of the POSIX specification of swprintf [1]:

==================================== foo1.c ====================================
#include <stdio.h>
#include <wchar.h>

int main ()
{
  static wint_t L_x = (wchar_t) 'x';
  wchar_t buf[12] =
    { 0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF,
      0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF };
  int ret = swprintf (buf, 12, L"%10lc", L_x);
  printf ("ret = %d, buf[0] = 0x%x, buf[1] = 0x%x, buf[9] = 0x%x, buf[10] = 0x%x, buf[11] = 0x%x\n",
          ret,
          (unsigned int) buf[0], (unsigned int) buf[1],
          (unsigned int) buf[9], (unsigned int) buf[10], (unsigned int) buf[11]);
  return 0;
}
/*
glibc:      ret = 10, buf[0] = 0x20, buf[1] = 0x20, buf[9] = 0x78, buf[10] = 0x0, buf[11] = 0xdeadbeef
musl libc:  ret = 1, buf[0] = 0x78, buf[1] = 0x0, buf[9] = 0xdeadbeef, buf[10] = 0xdeadbeef, buf[11] = 0xdeadbeef
*/
================================================================================

$ gcc -Wall foo1.c
$ ./a.out
ret = 1, buf[0] = 0x78, buf[1] = 0x0, buf[9] = 0xdeadbeef, buf[10] = 0xdeadbeef, buf[11] = 0xdeadbeef

The POSIX specification [1] says:
  "An optional minimum field width. If the converted value has fewer wide
   characters than the field width, it shall be padded with <space> characters
   by default on the left; it shall be padded on the right, if the left-
   adjustment flag ( '-' ), described below, is given to the field width. The
   field width takes the form of an <asterisk> ( '*' ), described below, or a
   decimal integer."

Here, the minimum field width specification of 10 was apparently ignored.

For comparison, in snprintf, this case is handled correctly:

==================================== foo2.c ====================================
#include <stdio.h>
#include <string.h>
#include <wchar.h>

int main ()
{
  static wint_t L_x = (wchar_t) 'x';
  char buf[12] = { 0xDD, 0xDD, 0xDD, 0xDD, 0xDD, 0xDD, 0xDD, 0xDD, 0xDD, 0xDD, 0xDD, 0xDD };
  int ret = snprintf (buf, 12, "%10lc", L_x);
  printf ("ret = %d, buf[0] = 0x%x, buf[1] = 0x%x, buf[9] = 0x%x, buf[10] = 0x%x, buf[11] = 0x%x\n",
          ret,
          (unsigned char) buf[0], (unsigned char) buf[1],
          (unsigned char) buf[9], (unsigned char) buf[10], (unsigned char) buf[11]);
  return 0;
}
/*
glibc:      ret = 10, buf[0] = 0x20, buf[1] = 0x20, buf[9] = 0x78, buf[10] = 0x0, buf[11] = 0xdd
musl libc:  ret = 10, buf[0] = 0x20, buf[1] = 0x20, buf[9] = 0x78, buf[10] = 0x0, buf[11] = 0xdd
*/
================================================================================

$ gcc -Wall foo1.c
$ ./a.out
ret = 10, buf[0] = 0x20, buf[1] = 0x20, buf[9] = 0x78, buf[10] = 0x0, buf[11] = 0xdd

Bruno

[1] https://pubs.opengroup.org/onlinepubs/9699919799/functions/swprintf.html

Re: [musl] swprintf: minimum width ignored for %lc

[Rich Felker]

On Mon, Mar 20, 2023 at 01:29:47AM +0100, Bruno Haible wrote:
> On musl-1.2.3 I see this violation of the POSIX specification of swprintf [1]:
> 
> ==================================== foo1.c ====================================
> #include <stdio.h>
> #include <wchar.h>
> 
> int main ()
> {
>   static wint_t L_x = (wchar_t) 'x';
>   wchar_t buf[12] =
>     { 0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF,
>       0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF, 0xDEADBEEF };
>   int ret = swprintf (buf, 12, L"%10lc", L_x);
>   printf ("ret = %d, buf[0] = 0x%x, buf[1] = 0x%x, buf[9] = 0x%x, buf[10] = 0x%x, buf[11] = 0x%x\n",
>           ret,
>           (unsigned int) buf[0], (unsigned int) buf[1],
>           (unsigned int) buf[9], (unsigned int) buf[10], (unsigned int) buf[11]);
>   return 0;
> }
> /*
> glibc:      ret = 10, buf[0] = 0x20, buf[1] = 0x20, buf[9] = 0x78, buf[10] = 0x0, buf[11] = 0xdeadbeef
> musl libc:  ret = 1, buf[0] = 0x78, buf[1] = 0x0, buf[9] = 0xdeadbeef, buf[10] = 0xdeadbeef, buf[11] = 0xdeadbeef
> */
> ================================================================================
> 
> $ gcc -Wall foo1.c
> $ ./a.out
> ret = 1, buf[0] = 0x78, buf[1] = 0x0, buf[9] = 0xdeadbeef, buf[10] = 0xdeadbeef, buf[11] = 0xdeadbeef
> 
> The POSIX specification [1] says:
>   "An optional minimum field width. If the converted value has fewer wide
>    characters than the field width, it shall be padded with <space> characters
>    by default on the left; it shall be padded on the right, if the left-
>    adjustment flag ( '-' ), described below, is given to the field width. The
>    field width takes the form of an <asterisk> ( '*' ), described below, or a
>    decimal integer."
> 
> Here, the minimum field width specification of 10 was apparently ignored.

Indeed, it's very clear from the code that it was just ignored. This
has a simple direct fix.

Rich