document setlocale(LC_ALL, null) to retrieve current setting

[remicollet]

Document how it works (since always)

ping @nielsdos as related to php/php-src#19070

[nielsdos]

Is this actually non-interactive?

[remicollet]

Don't know (1st time I see this attribute)
This is a copy-paste of the other example ;)

[nielsdos]

It is for enabling running the example code on the docs website. But okay, if the other does not have it, it likely has a reason.

[nielsdos]

Unfortunately, it seems more complicated than that.

A locale of "0" maps to NULL in the C code:
https://github.com/php/php-src/blob/c4183fba003a8601fcdf4d9530fa2f38e3e0c100/ext/standard/string.c#L4850-L4852

This means that setlocale(..., "0") in PHP does setlocale(..., NULL) in C.
NULL actually means returning the current locale without changing it. So the docs description was correct.

Passing NULL in PHP transforms it to the string "" in the C code, i.e. setlocale(..., NULL) in PHP does setlocale(..., "") in C, which means setting the locale to the user-preferred locale.

The difference between C/PHP should be cleared up in this page.

[remicollet]

Sorry, I merged the fix before seing your last comment.

This means that setlocale(..., "0") in PHP does setlocale(..., NULL) in C.

Yes, I noticed this part of the code, But this doesn't work

$ sapi/cli/php -r 'var_dump(setlocale(LC_ALL, null));'
string(11) "fr_FR.UTF-8"

$ sapi/cli/php -r 'var_dump(setlocale(LC_ALL, "0"));'
string(166) "LC_CTYPE=C.UTF-8;LC_NUMERIC=C;LC_TIME=C;LC_COLLATE=C;LC_MONETARY=C;LC_MESSAGES=C;LC_PAPER=C;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=C;LC_IDENTIFICATION=C"

Only null (or empty string) return the current setting

[remicollet]

glibc documentation seems terribly confusing

If locale is NULL, the current locale is only queried, not modified.

If locale is an empty string, "", each part of the locale that should be modified is set according to the environment variables.

And the example in https://sourceware.org/glibc/manual/latest/html_node/Setting-the-Locale.html

  /* Get the name of the current locale.  */
  old_locale = setlocale (LC_ALL, NULL);

Edit: understood

In C: null return the current setting from a previous call, empty string set and return setting (from env)

$ sapi/cli/php -r 'var_dump(setlocale(LC_ALL, "0"),setlocale(LC_ALL, null),setlocale(LC_ALL, "0"),setlocale(LC_ALL, "de_DE"),setlocale(LC_ALL, "0"));'
string(166) "LC_CTYPE=C.UTF-8;LC_NUMERIC=C;LC_TIME=C;LC_COLLATE=C;LC_MONETARY=C;LC_MESSAGES=C;LC_PAPER=C;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=C;LC_IDENTIFICATION=C"   <=  PHP default value
string(11) "fr_FR.UTF-8"    <= set from env
string(11) "fr_FR.UTF-8"
string(5) "de_DE"    <= set from arg
string(5) "de_DE"

[remicollet]

The difference between C/PHP should be cleared up in this page.

See PR #4770