casaroli opened a new pull request, #20544:
URL: https://github.com/apache/nuttx/pull/20544
## Summary
C99 specifies `%lc` for a wide character (`wint_t`) and `%ls` for a wide
string (`wchar_t *`), written as their multibyte sequences. `printf()` ignored
the `l` and handled them as `%c` and `%s`: `%lc` wrote only the low byte of the
character, and `%ls` read the wide string as bytes and stopped at the first
zero byte, which for ASCII text is after the first character.
For example, bash's `help` builds each line of its command list as a wide
string and prints it with `%ls`, so the list came out as lines of spaces.
With `CONFIG_LIBC_LOCALE`, this PR converts them with `wcrtomb()`. For `%ls`
the precision limits the number of bytes, and a character that does not fit is
not written in part. A character that cannot be converted makes `printf()` fail
with `EILSEQ`, as C99 specifies.
## Impact
Only with `CONFIG_LIBC_LOCALE` (existing option, default n). `printf()` is
in almost every image, so the conversion is built only with the locale support.
Without it, `%lc` and `%ls` behave as before.
## Testing
`qemu-armv8a:knsh`, QEMU 11, a test program:
```c
printf("[%ls]\n", L"abc");
printf("[%5ls][%-5ls]\n", L"ab", L"ab");
printf("[%.2ls]\n", L"abcd");
printf("[%lc][%lc]\n", (wint_t)L'x', (wint_t)0xe9);
n = snprintf(b, sizeof(b), "%ls", L"été");
printf("[%.1ls]\n", L"é");
```
Before (and without `CONFIG_LIBC_LOCALE`):
```
[a]
[ a][a ]
[a]
[x][?]
snprintf returned 1: [?]
[?] (a 2-byte character does not fit in 1 byte)
```
After, with `CONFIG_LIBC_LOCALE`:
```
[abc]
[ ab][ab ]
[ab]
[x][é]
snprintf returned 5: [été]
[] (a 2-byte character does not fit in 1 byte)
```
Builds with `-Wno-cpp -Werror`: `lm3s6965-ek:qemu-flat` and `mps2-an500:nsh`
as they are; `qemu-armv8a:nsh`, `qemu-armv8a:knsh`, `mps2-an500:nsh`,
`raspberrypi-pico:nsh`, `rv-virt:nsh` and `qemu-armv8a:nsh` with
`CONFIG_LIBC_NUMBERED_ARGS`, all with `CONFIG_LIBC_LOCALE`.
`tools/checkpatch.sh` reports only the "Bad alignment" errors that
`lib_libvsprintf.c` already has on master (its `case` labels are level with the
braces).
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