[Bug 215844] New: scanf manpage incorrectly says that ll (ell-ell) is equivalent to L

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=215844

            Bug ID: 215844
           Summary: scanf manpage incorrectly says that ll (ell-ell) is
                    equivalent to L
           Product: Documentation
           Version: unspecified
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P1
         Component: man-pages
          Assignee: documentation_man-pages@kernel-bugs.osdl.org
          Reporter: rootkea@gmail.com
        Regression: No

Hello!

manpage of scanf says that "Specifying two l characters is equivalent to L".
But that's not true.

Please check the following code snippet:
#include <stdio.h>

int main(void)
{
        long double ld;
        long long n;

        scanf("%Lf", &ld);
        scanf("%llf", &ld);

        scanf("%Ln", &n);
        scanf("%lln", &n);

        return 0;
}

gcc throws these warnings correctly:
warning: use of ‘ll’ length modifier with ‘f’ type character has either no
effect or undefined behavior [-Wformat=]
    9 |         scanf("%llf", &ld);
      |                   ^
warning: use of ‘L’ length modifier with ‘n’ type character has either no
effect or undefined behavior [-Wformat=]
   11 |         scanf("%Ln", &n);
      |                  ^

I think, we need to add separate entry for `ll` (ell-ell) like printf(3).

Also, another related issue is that scanf(3) doesn't mention that conversion
specifiers like `%Ld`, `%Li` etc. are GNU nonstandard extensions unlike
printf(3) which clearly mentions the nonportable part.

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