IssueTracker

The ISO C 23 standard specifies the return values of the functions mbrtoc32 (§ 7.30.1.5) and mbrtoc16 (§ 7.30.1.3). The return value 0 indicates that a "multibyte character that corresponds to the null wide character" was seen. The return value (size_t)(-2) indicate that no complete multibyte character could be parsed. When the input is empty, that is, the third argument is 0, the correct return value is (size_t)(-2). But in Bionic libc (in Android 11 at least) the return value is 0.

Test case:
========================= foo.c =========================
#include <stdio.h>
#include <uchar.h>
static char32_t wc;
static char16_t c16;
static mbstate_t mbs1;
static mbstate_t mbs2;
int
main (void)
{
  printf ("mbrtoc32 return value = %d\n", (int) mbrtoc32 (&wc, "", 0, &mbs1));
  printf ("mbrtoc16 return value = %d\n", (int) mbrtoc16 (&c16, "", 0, &mbs2));
}
========================================================

Compile and run this program (e.g. under termux).

Expected output (seen e.g. in musl libc, which is generally very standards compliant):
mbrtoc32 return value = -2
mbrtoc16 return value = -2

Actual output (on Android 11):
mbrtoc32 return value = 0
mbrtoc16 return value = 0