musl - printf doesn't respect locale

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Message-ID: <CAPy=dbJVxof7_HRqw_cSFdz1AfJkCvYPnQ4iRk+OysbRu7huDw@mail.gmail.com>
Date: Mon, 9 Sep 2019 17:31:01 +0100
From: Daniel Schoepe <daniel@...oepe.org>
To: musl@...ts.openwall.com
Subject: printf doesn't respect locale

Hi,

I think I found a discrepancy between musl's behavior and the POSIX standard:

According to the POSIX standard, the decimal separator used when using
printf to print floating point numbers should come from the locale
(https://pubs.opengroup.org/onlinepubs/9699919799/functions/fprintf.html):

"The radix character is defined in the current locale (category
LC_NUMERIC). In the POSIX locale, or in a locale where the radix
character is not defined, the radix character shall default to a
<period> ( '.' )."

However, it seems that in musl, a period is always used for printing
floating point numbers. For example, the following program prints
"12.0" instead of "12,0" (which is printed when using GNU libc):

#include <stdio.h>
#include <locale.h>

int main(int argc, char **argv) {
    setlocale(LC_ALL, "DE_de");
    printf("%f\n", 12.0f);
}

This was tested using the latest git checkout of musl
(a882841baf42e6a8b74cc33a239b84a9a79493db), compiled on Ubuntu 18.04
using the musl-gcc script. It looks like the usage of "." as a
separator is hardcoded in `fmt_fp`, for instance here:
https://git.musl-libc.org/cgit/musl/tree/src/stdio/vfprintf.c#n392

Best regards,
Daniel

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