commit 10de4a47ef3f481592e3c62eb07bcda23e9fde4d
Author: Arjun Shankar <arjun@redhat.com>
Date:   Mon Jul 29 14:30:59 2024 +0200

    manual/stdio: Clarify putc and putwc
    
    The manual entry for `putc' described what "most systems" do instead of
    describing the glibc implementation and its guarantees.  This commit
    fixes that by warning that putc may be implemented as a macro that
    double-evaluates `stream', and removing the performance claim.
    
    Even though the current `putc' implementation does not double-evaluate
    `stream', offering this obscure guarantee as an extension to what
    POSIX allows does not seem very useful.
    
    The entry for `putwc' is also edited to bring it in line with `putc'.
    Reviewed-by: Florian Weimer <fweimer@redhat.com>

diff --git a/manual/stdio.texi b/manual/stdio.texi
index fd7ed0cedc7c1a59..0c9a7ce4a9df4c05 100644
--- a/manual/stdio.texi
+++ b/manual/stdio.texi
@@ -903,21 +903,21 @@ This function is a GNU extension.
 @deftypefun int putc (int @var{c}, FILE *@var{stream})
 @standards{ISO, stdio.h}
 @safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{} @aculock{}}}
-This is just like @code{fputc}, except that most systems implement it as
+This is just like @code{fputc}, except that it may be implemented as
 a macro, making it faster.  One consequence is that it may evaluate the
 @var{stream} argument more than once, which is an exception to the
-general rule for macros.  @code{putc} is usually the best function to
-use for writing a single character.
+general rule for macros.  Therefore, @var{stream} should never be an
+expression with side-effects.
 @end deftypefun
 
 @deftypefun wint_t putwc (wchar_t @var{wc}, FILE *@var{stream})
 @standards{ISO, wchar.h}
 @safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{}}@acunsafe{@acucorrupt{} @aculock{}}}
-This is just like @code{fputwc}, except that it can be implement as
+This is just like @code{fputwc}, except that it may be implemented as
 a macro, making it faster.  One consequence is that it may evaluate the
 @var{stream} argument more than once, which is an exception to the
-general rule for macros.  @code{putwc} is usually the best function to
-use for writing a single wide character.
+general rule for macros.  Therefore, @var{stream} should never be an
+expression with side-effects.
 @end deftypefun
 
 @deftypefun int putc_unlocked (int @var{c}, FILE *@var{stream})