[RFC v1] libio/: Add [v]aprintf()

[Alejandro Colomar <alx@kernel.org>]

Signed-off-by: Alejandro Colomar <alx@kernel.org>
---

Hi Paul, Joseph,

Since nobody replied, I guess people are not strongly opposed to it, but
they probably want to see a patch before spending time with this.

Thus, I've written a patch (or a draft of a patch).

This is the first time I add a function to glibc, and I find it quite
difficult, so I'll need some help.  I've added the most obvious pieces:
the prototypes and the implementation.  However, this doesn't work at
all, so I guess I'm missing stuff.  Would you mind helping me figure out
what I'm missing (or what's wrong)?

I tried building this simple test program, but I get linker errors:

	#include <stdio.h>
	#include <stdlib.h>

	int
	main(void)
	{
		char *p;

		p = aprintf("foo %d", 42);
		if (p == NULL)
			exit(1);
		puts(p);
	}


Have a lovely night!
Alex


 libio/stdio.h    |  8 ++++++++
 libio/vaprintf.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+)
 create mode 100644 libio/vaprintf.c

diff --git a/libio/stdio.h b/libio/stdio.h
index 3bf6a1f6..3db363f1 100644
--- a/libio/stdio.h
+++ b/libio/stdio.h
@@ -410,6 +410,14 @@ extern int __asprintf (char **__restrict __ptr,
 extern int asprintf (char **__restrict __ptr,
 		     const char *__restrict __fmt, ...)
      __THROWNL __attribute__ ((__format__ (__printf__, 2, 3))) __wur;
+
+/* Write formatted output to a string dynamically allocated with `malloc'.  */
+extern char *vaprintf (const char *__restrict __f, __gnuc_va_list __arg)
+     __THROWNL __attribute__ ((__format__ (__printf__, 1, 0)))
+     __attribute_malloc__;
+extern char *aprintf (const char *__restrict __fmt, ...)
+     __THROWNL __attribute__ ((__format__ (__printf__, 1, 2)))
+     __attribute_malloc__;
 #endif
 
 #ifdef __USE_XOPEN2K8
diff --git a/libio/vaprintf.c b/libio/vaprintf.c
new file mode 100644
index 00000000..0ba147a0
--- /dev/null
+++ b/libio/vaprintf.c
@@ -0,0 +1,53 @@
+/* Copyright (C) 2026 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.
+
+   As a special exception, if you link the code in this file with
+   files compiled with a GNU compiler to produce an executable,
+   that does not cause the resulting executable to be covered by
+   the GNU Lesser General Public License.  This exception does not
+   however invalidate any other reasons why the executable file
+   might be covered by the GNU Lesser General Public License.
+   This exception applies to code released by its copyright holders
+   in files containing the exception.  */
+
+#include "libioP.h"
+#include <stdarg.h>
+#include <stddef.h>
+#include <stdio.h>
+
+char **
+__vaprintf (const char *fmt, va_list args)
+{
+  char *p;
+
+  return (__vasprintf_internal (&p, fmt, args, 0) < 0 ? NULL : p;
+}
+ldbl_weak_alias (__vaprintf, vaprintf)
+
+char **
+__aprintf (const char *fmt, ...)
+{
+  char *p;
+  va_list ap;
+
+  va_start(ap, fmt);
+  p = __vaprintf(fmt, ap);
+  va_end(ap);
+
+  return p;
+}
+ldbl_weak_alias (__aprintf, aprintf)

Range-diff against v0:
-:  -------- > 1:  e5defcbd libio/: Add [v]aprintf()
-- 
2.53.0