For review: newlocale.3

For review: newlocale.3

[Michael Kerrisk (man-pages)]

Hello all,

I've drafted a newlocale(3) man page. Review comments welcome.

Cheers,

Michael

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.TH NEWLOCALE 3 2014-03-12 "Linux" "Linux Programmer's Manual"
.SH NAME
newlocale, freelocale \- create, modify, and free a locale object
.SH SYNOPSIS
.nf
.B #include <locale.h>

.BI "locale_t newlocale(int " category_mask ", const char *" locale ",
.BI "                   locale_t " base );

.BI "void freelocale(locale_t " locobj );
.fi
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR newlocale (),
.BR freelocale ():
.PD 0
.RS 4
.TP
Since glibc 2.10:
_XOPEN_SOURCE\ >=\ 700
.TP
Before glibc 2.10:
_GNU_SOURCE
.RE
.PD
.SH DESCRIPTION
The
.BR newlocale ()
function creates a new locale object, or modifies an existing object,
returning a reference to the new or modified object as the function result.
Whether the call creates a new object or modifies an existing object
is determined by the value of
.IR base :
.IP * 3
If
.I base
is
.IR "(locale_t)\ 0" ,
a new object is created.
.IP *
If
.I base
refers to valid existing locale object
(i.e., an object returned by a previous call to
.BR newlocale ()
or
.BR duplocale (3)),
then that object is modified by the call.
If the call is successful, the contents of
.I base
are unspecified (in particular, the object referred to by
.I base
may be freed, and a new object created).
Therefore, the caller should ensure that it stops using
.I base
before the call to
.BR newlocale (),
and should subsequently refer to the modified object via the
reference returned as the function result.
If the call fails, the contents of
.I base
remain valid and unchanged.
.PP
The
.I category_mask
argument is a bit mask that specifies the locale categories
that are to be set in a newly created locale object
or modified in an existing object.
The mask is constructed by a bitwise OR of the constants
.BR LC_CTYPE_MASK ,
.BR LC_COLLATE_MASK ,
.BR LC_MESSAGES_MASK ,
.BR LC_MONETARY_MASK ,
.BR LC_NUMERIC_MASK ,
and
.BR LC_TIME_MASK .
For each category specified in
.IR category_mask ,
the locale data from
.I locale
will be used in the object returned by
.BR newlocale ().
If a new locale object is being created,
data for all categories not specified in
.IR category_mask
is taken from the default ("POSIX") locale.

The following preset values of
.I locale
are defined for all categories that can be specified in
.IR category_mask :
.TP
"POSIX"
A minimal locale environment for C language programs.
.TP
"C"
Equivalent to "POSIX".
.TP
""
An implementation-defined native environment
corresponding to the values of the
.BR LC_*
and
.B LANG
environment variables (see
.BR locale (7)).
.PP
If
.I base
is the special locale object
.BR LC_GLOBAL_LOCALE
(see
.BR duplocale (3)),
or is not
.IR "(locale_t)\ 0"
and is not a valid locale object handle,
the behavior is undefined.
.SS freelocale()
The
.BR freelocale ()
function deallocates the resources associated with
.IR locobj ,
a locale object previously returned by a call to
.BR newlocale ()
or
.BR duplocale (3).
If
.I locobj
is
.BR LC_GLOBAL_LOCALE
or is not valid locale object handle, the results are undefined.

Once a locale object has been freed,
the program should make no further use of it.
.SH RETURN VALUE
On success,
.BR newlocale ()
returns a handle that can be used in calls to
.BR duplocale (3),
.BR freelocale (),
and other functions that take a
.I locale_t
argument.
On error,
.BR newlocale ()
returns
.IR "(locale_t)\ 0",
and sets
.I errno
to indicate the cause of the error.
.SH ERRORS
.TP
.B EINVAL
One or more bits in
.I category_mask
does not correspond to a valid locale category.
.TP
.B EINVAL
.I locale
is NULL.
.TP
.B ENOENT
.I locale
is not a string pointer referring to a valid locale.
.TP
.B ENOMEM
Insufficient memory to create a locale object.
.SH VERSIONS
The
.BR newlocale ()
and
.BR freelocale ()
functions first appeared in version 2.3 of the GNU C library.
.SH CONFORMING TO
POSIX.1-2008.
.SH NOTES
Each locale object created by
.BR newlocale ()
should be deallocated using
.BR freelocale (3).
.SH EXAMPLE
The program below takes up to two command-line arguments,
which each identify locales.
The first argument is required, and is used to set the
.B LC_NUMERIC
category in a locale object created using
.BR newlocale ().
The second command-line argument is optional;
if it is present, it is used to set the
.B LC_TIME
category of the locale object.

Having created and initialized the locale object,
the program then applies it using
.BR uselocale (),
and then tests the effect of the locale changes by:
.IP 1. 3
Displaying a floating-point number with a fractional part.
This output will be affected by the
.B LC_NUMERIC
setting.
In many European-language locales,
the fractional part of the number is separated from the integer part
using a comma, rather than a period.
.IP 2.
Displaying the date.
The format and language of the output will be affected by the
.B LC_TIME
setting.

.PP
The following shell sessions show some example runs of this program.

Set the
.B LC_NUMERIC
category to
.IR fr_FR
(French):
.in +4n
.nf

$ \fB./a.out fr_FR\fP
123456,789
Fri Mar  7 00:25:08 2014
.fi
.in

Set the
.B LC_NUMERIC
category to
.IR fr_FR
(French),
and the
.B LC_TIME
category to
.IR it_IT
(Italian):
.in +4n
.nf

$ \fB./a.out fr_FR it_IT\fP
123456,789
ven 07 mar 2014 00:26:01 CET
.fi
.in

Specify the
.B LC_TIME
setting as an empty string,
which causes the value to be taken from environment variable settings
(which, here, specify
.IR mi_NZ ,
New Zealand Māori):
.in +4n
.nf

$ LC_ALL=mi_NZ ./a.out fr_FR ""
123456,789
Te Paraire, te 07 o Poutū-te-rangi, 2014 00:38:44 CET
.fi
.in

.in +4n
.nf

.fi
.in
.SS Program source
.nf
#define _XOPEN_SOURCE 700
#include <stdio.h>
#include <stdlib.h>
#include <locale.h>
#include <time.h>

#define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \\
                        } while (0)

int
main(int argc, char *argv[])
{
    const int BUF_SIZE = 100;
    char buf[BUF_SIZE];
    time_t t;
    size_t s;
    struct tm *tm;
    locale_t loc, nloc;

    if (argc < 2) {
        fprintf(stderr, "Usage: %s locale1 [locale2]\\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    /* Create a new locale object, taking the LC_NUMERIC settings
       from the locale specified in argv[1] */

    loc = newlocale(LC_NUMERIC_MASK, argv[1], (locale_t) 0);
    if (loc == (locale_t) 0)
        errExit("newlocale");

    /* If a second command\-line argument was specified, modify the
       locale object to take the LC_TIME settings from the locale
       specified in argv[2] */

    if (argc > 2) {
        nloc = newlocale(LC_TIME_MASK, argv[2], loc);
        if (loc == (locale_t) 0)
            errExit("newlocale");
        loc = nloc;
    }

    /* Apply the newly created locale to this thread */

    uselocale(loc);

    /* Test effect of LC_NUMERIC */

    printf("%8.3f\\n", 123456.789);

    /* Test effect of LC_TIME */

    t = time(NULL);
    tm = localtime(&t);
    if (tm == NULL)
        errExit("time");

    s = strftime(buf, BUF_SIZE, "%c", tm);
    if (s == 0)
        errExit("strftime");

    printf("%s\\n", buf);

    /* Free the locale object */

    freelocale(loc);

    exit(EXIT_SUCCESS);
}
.fi
.SH SEE ALSO
.BR locale (1),
.BR duplocale (3),
.BR setlocale (3),
.BR uselocale (3),
.BR locale (5),
.BR locale (7)



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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Re: For review: newlocale.3

[Mike Frysinger]

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On Wed 12 Mar 2014 16:47:43 Michael Kerrisk wrote:
> .SH DESCRIPTION
> The
> .BR newlocale ()
> function creates a new locale object, or modifies an existing object,
> returning a reference to the new or modified object as the function result.
> Whether the call creates a new object or modifies an existing object
> is determined by the value of
> .IR base :

you discuss the value of |base| first ...

> .PP
> The
> .I category_mask

... then the |category_mask| ...

> The following preset values of
> .I locale

... then the |locale| ...

(side note: shouldn't there be a .PP to start this portion ?)

> .PP
> If
> .I base

... then back to |base| ?  generally i expect the discussion of each argument 
to be together rather than split across paragraphs.  if i were referring to 
this for programming, i probably wouldn't have even made it this far.

> .B EINVAL
> One or more bits in
> .I category_mask
> does not correspond to a valid locale category.

does->do

> Having created and initialized the locale object,
> the program then applies it using
> .BR uselocale (),

shouldn't that be (3) ?

> Te Paraire, te 07 o Poutū-te-rangi, 2014 00:38:44 CET
> .fi
> .in
> 
> .in +4n
> .nf
> 
> .fi
> .in
> .SS Program source

this ends up rendering 3 blank lines before "Program source" when really only 
one is needed

> .nf
> #define _XOPEN_SOURCE 700
> #include <stdio.h>
> #include <stdlib.h>
> #include <locale.h>
> #include <time.h>
> 
> #define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \\
>                         } while (0)

not sure what standard you're aiming for, but if you include err.h, you don't 
need this macro.  you can just call err(1, msg).

>     if (argc > 2) {
>         nloc = newlocale(LC_TIME_MASK, argv[2], loc);
>         if (loc == (locale_t) 0)

shouldn't you be testing nloc ?

if you're just going to exit on error, i wonder why even bother with nloc 
indirection

>     s = strftime(buf, BUF_SIZE, "%c", tm);

why not sizeof(buf) ?  avoids needing BUF_SIZE at all.
-mike

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Re: For review: newlocale.3

[Michael Kerrisk (man-pages)]

Hi Mike,

On Thu, Mar 13, 2014 at 9:13 AM, Mike Frysinger <vapier-aBrp7R+bbdUdnm+yROfE0A@public.gmane.org> wrote:
> On Wed 12 Mar 2014 16:47:43 Michael Kerrisk wrote:
>> .SH DESCRIPTION
>> The
>> .BR newlocale ()
>> function creates a new locale object, or modifies an existing object,
>> returning a reference to the new or modified object as the function result.
>> Whether the call creates a new object or modifies an existing object
>> is determined by the value of
>> .IR base :
>
> you discuss the value of |base| first ...
>
>> .PP
>> The
>> .I category_mask
>
> ... then the |category_mask| ...
>
>> The following preset values of
>> .I locale
>
> ... then the |locale| ...
>
> (side note: shouldn't there be a .PP to start this portion ?)

Yup, better. Added.

>> .PP
>> If
>> .I base
>
> ... then back to |base| ?  generally i expect the discussion of each argument
> to be together rather than split across paragraphs.  if i were referring to
> this for programming, i probably wouldn't have even made it this far.

Okay -- I moved that para to go with the rest of the description of 'base'.

>> .B EINVAL
>> One or more bits in
>> .I category_mask
>> does not correspond to a valid locale category.
>
> does->do

Fixed.

>> Having created and initialized the locale object,
>> the program then applies it using
>> .BR uselocale (),
>
> shouldn't that be (3) ?

Yup.

>> Te Paraire, te 07 o Poutū-te-rangi, 2014 00:38:44 CET
>> .fi
>> .in
>>
>> .in +4n
>> .nf
>>
>> .fi
>> .in
>> .SS Program source
>
> this ends up rendering 3 blank lines before "Program source" when really only
> one is needed

Funny, id didn't render that way for me. However, the above piece is
obviously cruft, and I removed it ;-).

>> .nf
>> #define _XOPEN_SOURCE 700
>> #include <stdio.h>
>> #include <stdlib.h>
>> #include <locale.h>
>> #include <time.h>
>>
>> #define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \\
>>                         } while (0)
>
> not sure what standard you're aiming for, but if you include err.h, you don't
> need this macro.  you can just call err(1, msg).

I tend to avoid those functions because they're nonstandard (some of
the examples in man pages do compile and sun on non-Linux systems).
So, I just roll my own short macros.

>>     if (argc > 2) {
>>         nloc = newlocale(LC_TIME_MASK, argv[2], loc);
>>         if (loc == (locale_t) 0)
>
> shouldn't you be testing nloc ?

Yup!

> if you're just going to exit on error, i wonder why even bother with nloc
> indirection

More to illustrate the point that this is how to do things generally
(i.e., we might be doing something other than exiting on error). I've
added a comment explaining this.

>>     s = strftime(buf, BUF_SIZE, "%c", tm);
>
> why not sizeof(buf) ?  avoids needing BUF_SIZE at all.

Yes, simpler. Done.

Thanks for the comments, Mike.

Cheers,

Michael



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
--
To unsubscribe from this list: send the line "unsubscribe linux-man" in
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Re: For review: newlocale.3

[Michael Kerrisk (man-pages)]

Hi Mike,

On Thu, Mar 13, 2014 at 9:13 AM, Mike Frysinger <vapier-aBrp7R+bbdUdnm+yROfE0A@public.gmane.org> wrote:
> On Wed 12 Mar 2014 16:47:43 Michael Kerrisk wrote:
>> .SH DESCRIPTION
>> The
>> .BR newlocale ()
>> function creates a new locale object, or modifies an existing object,
>> returning a reference to the new or modified object as the function result.
>> Whether the call creates a new object or modifies an existing object
>> is determined by the value of
>> .IR base :
>
> you discuss the value of |base| first ...
>
>> .PP
>> The
>> .I category_mask
>
> ... then the |category_mask| ...
>
>> The following preset values of
>> .I locale
>
> ... then the |locale| ...
>
> (side note: shouldn't there be a .PP to start this portion ?)

Yup, better. Added.

>> .PP
>> If
>> .I base
>
> ... then back to |base| ?  generally i expect the discussion of each argument
> to be together rather than split across paragraphs.  if i were referring to
> this for programming, i probably wouldn't have even made it this far.

Okay -- I moved that para to go with the rest of the description of 'base'.

>> .B EINVAL
>> One or more bits in
>> .I category_mask
>> does not correspond to a valid locale category.
>
> does->do

Fixed.

>> Having created and initialized the locale object,
>> the program then applies it using
>> .BR uselocale (),
>
> shouldn't that be (3) ?

Yup.

>> Te Paraire, te 07 o Poutū-te-rangi, 2014 00:38:44 CET
>> .fi
>> .in
>>
>> .in +4n
>> .nf
>>
>> .fi
>> .in
>> .SS Program source
>
> this ends up rendering 3 blank lines before "Program source" when really only
> one is needed

Funny, id didn't render that way for me. However, the above piece is
obviously cruft, and I removed it ;-).

>> .nf
>> #define _XOPEN_SOURCE 700
>> #include <stdio.h>
>> #include <stdlib.h>
>> #include <locale.h>
>> #include <time.h>
>>
>> #define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \\
>>                         } while (0)
>
> not sure what standard you're aiming for, but if you include err.h, you don't
> need this macro.  you can just call err(1, msg).

I tend to avoid those functions because they're nonstandard (some of
the examples in man pages do compile and sun on non-Linux systems).
So, I just roll my own short macros.

>>     if (argc > 2) {
>>         nloc = newlocale(LC_TIME_MASK, argv[2], loc);
>>         if (loc == (locale_t) 0)
>
> shouldn't you be testing nloc ?

Yup!

> if you're just going to exit on error, i wonder why even bother with nloc
> indirection

More to illustrate the point that this is how to do things generally
(i.e., we might be doing something other than exiting on error). I've
added a comment explaining this.

>>     s = strftime(buf, BUF_SIZE, "%c", tm);
>
> why not sizeof(buf) ?  avoids needing BUF_SIZE at all.

Yes, simpler. Done.

Thanks for the comments, Mike.

Cheers,

Michael



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
--
To unsubscribe from this list: send the line "unsubscribe linux-man" in
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