[Bug stdio/22672] New: Problems with sscanf parsing certain hex-floats

["BM-2cUWXLL9JqDWpsk8EivFHCgbsbXFtsxQrk at bitmessage dot ch" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=22672

            Bug ID: 22672
           Summary: Problems with sscanf parsing certain hex-floats
           Product: glibc
           Version: 2.26
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: stdio
          Assignee: unassigned at sourceware dot org
          Reporter: BM-2cUWXLL9JqDWpsk8EivFHCgbsbXFtsxQrk at bitmessage dot ch
  Target Milestone: ---

Created attachment 10712
  --> https://sourceware.org/bugzilla/attachment.cgi?id=10712&action=edit
example code, visualizing the behavior from above

Assume `d` as a normal double variable.
Executing
`sscanf ( "0x", "%lf", &d )`
returns `0` and `d` isn't modified, 'cause the string can't be parsed.
I think that 0x indicates in correspondence with `%lf`, that there seem to be a
maybe slightly incomplete hex-float.

But wouldn't it be a better behavior if this statement is correctly parsed into
the double `d` with the value `0`, 'cause ignoring the `x` and correctly
parsing `0` as well as assuming that `0x` originally means `0x0` is a much more
thought-out behavior than just saying "sry, but this can't be parsed, so it's
better doing nothing"?
Even though `sscanf ( "0x", "%i", &i )` returns successfully `1` and the
integer value `i` is going to have the value `0`. Furthermore e.g. BSD'
versions of GCC on MacOS correctly parses the 0x-lf case...

I'm using a x86_64-pc-linux-gnu 4.14.9-Linux to compile the code using
GCC-7.2.1 without any significant options (no compiler warnings present).
Thanks!

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