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Re: [Libvir] [PATCH] Enhance virBuffer code



Jim Meyering wrote:
"Richard W.M. Jones" <rjones redhat com> wrote:
Jim Meyering wrote:
What do you think of using this?

  isascii (*p) && isalnum (*p)
I'm not sure I'm qualified to say what this does on EBCDIC, but quite
likely lots of other code breaks there too anyway.  This is nicely
self-documenting anyway.

As Daniel suggested, isalnum is locale-sensitive.
If there's a locale with an alphabetic byte that is outside
the logical a-zA-Z range, yet still within 0..127, then the above
expression will give a false-positive for that byte.

I've been inclined to stop worrying about EBCDIC for years, but a quick
search on the web finds that people are still stuck using it, and do
report bugs in ASCII-assuming code.

This is why autoconf goes to the trouble of doing this:
  tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
not this:
  tr a-z A-Z
to convert to upper case.

Another factor to consider here is that it doesn't matter if this function over-escapes, but it does matter if the function under-escapes. That is to say, it could escape every character as a %xx hex code, which would be ugly and slightly inefficient but not wrong.

Rich.

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