File opening modes (r, w, a ...)

[jfong at ms4.hinet.net]

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