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Date: Tue, 10 Sep 2019 20:43:12 +0200
From: Szabolcs Nagy <>
To: Daniel Schoepe <>
Subject: Re: printf doesn't respect locale

* Daniel Schoepe <> [2019-09-10 18:10:20 +0100]:
> Basically, someone used printf to produce json output and was unaware
> that the radix used by printf was locale-dependent. When this was run
> on a system with a non-English locale, it no longer produced valid
> JSON as output.

ok, i thought using '.' unconditionally caused some problem.

i've seen plenty issues with locale dependent radix point
when numbers unexpectedly have ',', but the current musl
behaviour exactly prevents those types of bugs and i'd
prefer to keep it that way.

simple scripts parsing some program output will not be tested
across different locales. global state dependence is bad in
general in systems software which often communicates between
machines, not humans, and you cant afford to synchronize that
global state or deal with its combinatorics. in particular
libraries can't use any api with global state dependence if
that state may change asynchronously, thread-local state is
a bit better (and since posix2008 locales can be thread-local),
but it still has issues e.g. dprintf is implemented to be
async-signal-safe, but in a signal handler you can't change
the locale setting to get reliable dprintf behaviour and
it's inefficient/inconvenient to save/restore tls state
around every printf call anyway.

i think libc should mainly aim for reliability of systems
software and not for friendliness of ui applications.

> Best,
> Daniel
> On Tue, Sep 10, 2019 at 5:31 PM Szabolcs Nagy <> wrote:
> >
> > * Daniel Schoepe <> [2019-09-10 17:00:49 +0100]:
> > > I'm also not a fan of this behavior, I actually stumbled across this
> > > when tracking
> > > down a bug the different radix usage caused.
> >
> > i'm interested in how this can cause a bug in correct software.

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