[PATCH 1/2] man/man7/feature_test_macros.7: Add _ISOC23_SOURCE, _ISOC2X_SOURCE

[PATCH 1/2] man/man7/feature_test_macros.7: Add _ISOC23_SOURCE, _ISOC2X_SOURCE

[Mark Harris]

_ISOC2X_SOURCE has been recognized since glibc 2.31 (2020).[1]
_ISOC23_SOURCE has been recognized since glibc 2.40 (2024).[2]

[1] <https://sourceware.org/git/?p=glibc.git;a=commit;h=777d75fbc07b>
[2] <https://sourceware.org/git/?p=glibc.git;a=commit;h=42cc619dfbc4>

Signed-off-by: Mark Harris <mark.hsj@gmail.com>
---
 man/man7/feature_test_macros.7 | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/man/man7/feature_test_macros.7 b/man/man7/feature_test_macros.7
index f0d4a51f2..a0c97f2c5 100644
--- a/man/man7/feature_test_macros.7
+++ b/man/man7/feature_test_macros.7
@@ -358,6 +358,24 @@ .SS Feature test macros understood by glibc
 .I \-std=c11
 produces the same effects as defining this macro.
 .TP
+.BR _ISOC23_SOURCE " (since glibc 2.40)"
+Exposes declarations consistent with the ISO C23 standard.
+.IP
+Since glibc 2.31, an equivalent macro named
+.B _ISOC2X_SOURCE
+was recognized
+(because the C23 standard had not then been finalized).
+Although the use of this macro is obsolete, glibc continues
+to recognize it for backward compatibility.
+.IP
+Defining
+.B _ISOC23_SOURCE
+also enables C11, C99, and C95 features.
+.IP
+Invoking the C compiler with the option
+.I \-std=c23
+produces the same effects as defining this macro.
+.TP
 .B _LARGEFILE64_SOURCE
 Expose definitions for the alternative API specified by the
 LFS (Large File Summit) as a "transitional extension" to the
@@ -692,6 +710,8 @@ .SS Default definitions, implicit definitions, and combining definitions
 .BR _ISOC99_SOURCE ,
 .B _ISOC11_SOURCE
 (since glibc 2.18),
+.B _ISOC23_SOURCE
+(since glibc 2.40),
 .BR _POSIX_SOURCE ,
 .BR _POSIX_C_SOURCE  ,
 .BR _XOPEN_SOURCE ,
@@ -876,6 +896,10 @@ .SS Program source
     printf("_ISOC11_SOURCE defined\[rs]n");
 #endif
 \&
+#ifdef _ISOC23_SOURCE
+    printf("_ISOC23_SOURCE defined\[rs]n");
+#endif
+\&
 #ifdef _XOPEN_SOURCE
     printf("_XOPEN_SOURCE defined: %d\[rs]n", _XOPEN_SOURCE);
 #endif
-- 
2.52.0

[PATCH 2/2] man/man7/feature_test_macros.7: Drop _ISOC9X_SOURCE

[Mark Harris]

_ISOC9X_SOURCE was a temporary macro for use before the final name
of the standard was known.  It became obsolete when _ISOC99_SOURCE
was added in glibc 2.1.3 (1999), and has not been recognized since
_ISOC11_SOURCE was added in glibc 2.16 (2012).[1]

[1] <https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=d78099052b6b>

Signed-off-by: Mark Harris <mark.hsj@gmail.com>
---
 man/man7/feature_test_macros.7 | 11 +----------
 1 file changed, 1 insertion(+), 10 deletions(-)

diff --git a/man/man7/feature_test_macros.7 b/man/man7/feature_test_macros.7
index a0c97f2c5..76d6e44cd 100644
--- a/man/man7/feature_test_macros.7
+++ b/man/man7/feature_test_macros.7
@@ -333,16 +333,7 @@ .SS Feature test macros understood by glibc
 .TP
 .BR _ISOC99_SOURCE " (since glibc 2.1.3)"
 Exposes declarations consistent with the ISO C99 standard.
-.IP
-Earlier glibc 2.1.x versions recognized an equivalent macro named
-.B _ISOC9X_SOURCE
-(because the C99 standard had not then been finalized).
-Although the use of this macro is obsolete, glibc continues
-to recognize it for backward compatibility.
-.IP
-Defining
-.B _ISOC99_SOURCE
-also exposes ISO C (1990) Amendment 1 ("C95") definitions.
+Defining this macro also exposes ISO C (1990) Amendment 1 ("C95") definitions.
 (The primary change in C95 was support for international character sets.)
 .IP
 Invoking the C compiler with the option
-- 
2.52.0

Re: [PATCH 1/2] man/man7/feature_test_macros.7: Add _ISOC23_SOURCE, _ISOC2X_SOURCE

[Mark Harris]

On Tue, Jan 27, 2026 Mark Harris wrote:
>
> _ISOC2X_SOURCE has been recognized since glibc 2.31 (2020).[1]
> _ISOC23_SOURCE has been recognized since glibc 2.40 (2024).[2]
>
> [1] <https://sourceware.org/git/?p=glibc.git;a=commit;h=777d75fbc07b>
> [2] <https://sourceware.org/git/?p=glibc.git;a=commit;h=42cc619dfbc4>
>
> Signed-off-by: Mark Harris <mark.hsj@gmail.com>
> ---
>  man/man7/feature_test_macros.7 | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
>
> diff --git a/man/man7/feature_test_macros.7 b/man/man7/feature_test_macros.7
> index f0d4a51f2..a0c97f2c5 100644
> --- a/man/man7/feature_test_macros.7
> +++ b/man/man7/feature_test_macros.7
> @@ -358,6 +358,24 @@ .SS Feature test macros understood by glibc
>  .I \-std=c11
>  produces the same effects as defining this macro.
>  .TP
> +.BR _ISOC23_SOURCE " (since glibc 2.40)"
> +Exposes declarations consistent with the ISO C23 standard.
> +.IP
> +Since glibc 2.31, an equivalent macro named
> +.B _ISOC2X_SOURCE
> +was recognized
> +(because the C23 standard had not then been finalized).
> +Although the use of this macro is obsolete, glibc continues
> +to recognize it for backward compatibility.
> +.IP
> +Defining
> +.B _ISOC23_SOURCE
> +also enables C11, C99, and C95 features.
> +.IP
> +Invoking the C compiler with the option
> +.I \-std=c23
> +produces the same effects as defining this macro.
> +.TP
>  .B _LARGEFILE64_SOURCE
>  Expose definitions for the alternative API specified by the
>  LFS (Large File Summit) as a "transitional extension" to the
> @@ -692,6 +710,8 @@ .SS Default definitions, implicit definitions, and combining definitions
>  .BR _ISOC99_SOURCE ,
>  .B _ISOC11_SOURCE
>  (since glibc 2.18),
> +.B _ISOC23_SOURCE
> +(since glibc 2.40),
>  .BR _POSIX_SOURCE ,
>  .BR _POSIX_C_SOURCE  ,
>  .BR _XOPEN_SOURCE ,
> @@ -876,6 +896,10 @@ .SS Program source
>      printf("_ISOC11_SOURCE defined\[rs]n");
>  #endif
>  \&
> +#ifdef _ISOC23_SOURCE
> +    printf("_ISOC23_SOURCE defined\[rs]n");
> +#endif
> +\&
>  #ifdef _XOPEN_SOURCE
>      printf("_XOPEN_SOURCE defined: %d\[rs]n", _XOPEN_SOURCE);
>  #endif
> --
> 2.52.0
>

Ping on these 4 patches:

[PATCH 1/2] man/man7/feature_test_macros.7: Add _ISOC23_SOURCE, _ISOC2X_SOURCE
[PATCH 2/2] man/man7/feature_test_macros.7: Drop _ISOC9X_SOURCE
(https://lore.kernel.org/linux-man/c52b599edf72f3e536ff6a5b846232ab15bc83d7.1769581650.git.mark.hsj@gmail.com/T/)

[PATCH v3 1/2] man/man3/timespec_get.3: Refactor to prepare for new time bases
[PATCH v3 2/2] man/man3/timespec_get.3: Add ISO C23 time bases
(https://lore.kernel.org/linux-man/ec8dfdc495cb8d58e945b370658c6945cb424327.1769705123.git.mark.hsj@gmail.com/T/#u)


 - Mark

Re: [PATCH 1/2] man/man7/feature_test_macros.7: Add _ISOC23_SOURCE, _ISOC2X_SOURCE

[Alejandro Colomar]

[-- Attachment #1: Type: text/plain, Size: 967 bytes --]

Hi Mark,

On Thu, Feb 05, 2026 at 09:01:34AM -0800, Mark Harris wrote:
> Ping on these 4 patches:

Yup; sorry.  I'm a bit busy with C Committee meetings and preparing the
next release for this or next week.  I'll be back to reviewing
non-trivial or non-urgent patches next week or so.


Have a lovely day!
Alex

> 
> [PATCH 1/2] man/man7/feature_test_macros.7: Add _ISOC23_SOURCE, _ISOC2X_SOURCE
> [PATCH 2/2] man/man7/feature_test_macros.7: Drop _ISOC9X_SOURCE
> (https://lore.kernel.org/linux-man/c52b599edf72f3e536ff6a5b846232ab15bc83d7.1769581650.git.mark.hsj@gmail.com/T/)
> 
> [PATCH v3 1/2] man/man3/timespec_get.3: Refactor to prepare for new time bases
> [PATCH v3 2/2] man/man3/timespec_get.3: Add ISO C23 time bases
> (https://lore.kernel.org/linux-man/ec8dfdc495cb8d58e945b370658c6945cb424327.1769705123.git.mark.hsj@gmail.com/T/#u)
> 
> 
>  - Mark
> 

-- 
<https://www.alejandro-colomar.es>
Use port 80 (that is, <...:80/>).

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH 1/2] man/man7/feature_test_macros.7: Add _ISOC23_SOURCE, _ISOC2X_SOURCE

[Alejandro Colomar]

[-- Attachment #1: Type: text/plain, Size: 2330 bytes --]

On 2026-01-27T22:46:23-0800, Mark Harris wrote:
> _ISOC2X_SOURCE has been recognized since glibc 2.31 (2020).[1]
> _ISOC23_SOURCE has been recognized since glibc 2.40 (2024).[2]
> 
> [1] <https://sourceware.org/git/?p=glibc.git;a=commit;h=777d75fbc07b>
> [2] <https://sourceware.org/git/?p=glibc.git;a=commit;h=42cc619dfbc4>
> 
> Signed-off-by: Mark Harris <mark.hsj@gmail.com>

Hi Mark,

Thanks!  I've applied the patch.

Have a lovely night!
Alex

> ---
>  man/man7/feature_test_macros.7 | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/man/man7/feature_test_macros.7 b/man/man7/feature_test_macros.7
> index f0d4a51f2..a0c97f2c5 100644
> --- a/man/man7/feature_test_macros.7
> +++ b/man/man7/feature_test_macros.7
> @@ -358,6 +358,24 @@ .SS Feature test macros understood by glibc
>  .I \-std=c11
>  produces the same effects as defining this macro.
>  .TP
> +.BR _ISOC23_SOURCE " (since glibc 2.40)"
> +Exposes declarations consistent with the ISO C23 standard.
> +.IP
> +Since glibc 2.31, an equivalent macro named
> +.B _ISOC2X_SOURCE
> +was recognized
> +(because the C23 standard had not then been finalized).
> +Although the use of this macro is obsolete, glibc continues
> +to recognize it for backward compatibility.
> +.IP
> +Defining
> +.B _ISOC23_SOURCE
> +also enables C11, C99, and C95 features.
> +.IP
> +Invoking the C compiler with the option
> +.I \-std=c23
> +produces the same effects as defining this macro.
> +.TP
>  .B _LARGEFILE64_SOURCE
>  Expose definitions for the alternative API specified by the
>  LFS (Large File Summit) as a "transitional extension" to the
> @@ -692,6 +710,8 @@ .SS Default definitions, implicit definitions, and combining definitions
>  .BR _ISOC99_SOURCE ,
>  .B _ISOC11_SOURCE
>  (since glibc 2.18),
> +.B _ISOC23_SOURCE
> +(since glibc 2.40),
>  .BR _POSIX_SOURCE ,
>  .BR _POSIX_C_SOURCE  ,
>  .BR _XOPEN_SOURCE ,
> @@ -876,6 +896,10 @@ .SS Program source
>      printf("_ISOC11_SOURCE defined\[rs]n");
>  #endif
>  \&
> +#ifdef _ISOC23_SOURCE
> +    printf("_ISOC23_SOURCE defined\[rs]n");
> +#endif
> +\&
>  #ifdef _XOPEN_SOURCE
>      printf("_XOPEN_SOURCE defined: %d\[rs]n", _XOPEN_SOURCE);
>  #endif
> -- 
> 2.52.0
> 

-- 
<https://www.alejandro-colomar.es>

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH 2/2] man/man7/feature_test_macros.7: Drop _ISOC9X_SOURCE

[Alejandro Colomar]

[-- Attachment #1: Type: text/plain, Size: 1646 bytes --]

On 2026-01-27T22:46:24-0800, Mark Harris wrote:
> _ISOC9X_SOURCE was a temporary macro for use before the final name
> of the standard was known.  It became obsolete when _ISOC99_SOURCE
> was added in glibc 2.1.3 (1999), and has not been recognized since
> _ISOC11_SOURCE was added in glibc 2.16 (2012).[1]
> 
> [1] <https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=d78099052b6b>
> 
> Signed-off-by: Mark Harris <mark.hsj@gmail.com>

Patch applied.  Thanks!

Cheers,
Alex

> ---
>  man/man7/feature_test_macros.7 | 11 +----------
>  1 file changed, 1 insertion(+), 10 deletions(-)
> 
> diff --git a/man/man7/feature_test_macros.7 b/man/man7/feature_test_macros.7
> index a0c97f2c5..76d6e44cd 100644
> --- a/man/man7/feature_test_macros.7
> +++ b/man/man7/feature_test_macros.7
> @@ -333,16 +333,7 @@ .SS Feature test macros understood by glibc
>  .TP
>  .BR _ISOC99_SOURCE " (since glibc 2.1.3)"
>  Exposes declarations consistent with the ISO C99 standard.
> -.IP
> -Earlier glibc 2.1.x versions recognized an equivalent macro named
> -.B _ISOC9X_SOURCE
> -(because the C99 standard had not then been finalized).
> -Although the use of this macro is obsolete, glibc continues
> -to recognize it for backward compatibility.
> -.IP
> -Defining
> -.B _ISOC99_SOURCE
> -also exposes ISO C (1990) Amendment 1 ("C95") definitions.
> +Defining this macro also exposes ISO C (1990) Amendment 1 ("C95") definitions.
>  (The primary change in C95 was support for international character sets.)
>  .IP
>  Invoking the C compiler with the option
> -- 
> 2.52.0
> 

-- 
<https://www.alejandro-colomar.es>

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]