File opening modes (r, w, a ...)
jfong at ms4.hinet.net
jfong at ms4.hinet.net
Thu Feb 22 23:15:49 EST 2018
Lew Pitcher於 2018年2月23日星期五 UTC+8上午9時43分19秒寫道:
> jfong at ms4.hinet.net wrote:
>
> > ast於 2018年2月22日星期四 UTC+8下午8時33分00秒寫道:
> >> Hello
> >>
> >> I share a very valuable table I found on
> >> StackOverflow about file opening modes
> >>
> >> If like me you always forget the details of
> >> file opening mode, the following table provides
> >> a good summary
> >>
> >> | r r+ w w+ a a+
> >> ------------------|--------------------------
> >> read | + + + +
> >> write | + + + + +
> >> write after seek | + + +
> >> create | + + + +
> >> truncate | + +
> >> position at start | + + + +
> >> position at end | + +
> >
> > What the "write after seek" means?
>
> It /should/ mean that programs are permitted to seek to a point in the file,
> and then write from that point on.
>
> A write to a read mode ("r") file isn't permitted at all,
> so neither is "write after seek" to a read mode file.
>
> A write to an append mode ("a" and "a+") file always write to the end of the
> file, effectively negating any seek.
>
> HTH
>
> --
> Lew Pitcher
> "In Skills, We Trust"
> PGP public key available upon request
Thank you for explanation.
Mode 'r+', 'a' and 'a+' all can be seek and write, but only 'r+' was marked in the table. That's why I was confused. This row seems redundant to me:-)
--Jach
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