errno man page query

errno man page query

[Jon Grant]

Hello

Quoting from this page:

http://man7.org/linux/man-pages/man3/errno.3.html

"a function that succeeds is allowed to change errno."

^ This sounds clear, e.g. open() can change errno to 0, when it returns 
a valid fd handle.


"Valid error numbers are all nonzero; errno is never set to zero by any 
system
        call or library function."

^ This seems to be counter what the earlier line said. Therefore, open() 
wouldn't be allowed to change errno to 0.

Have I missed something?

Best regards, Jon
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Re: errno man page query

[Michael Kerrisk (man-pages)]

Hi Jon,

On Sun, Apr 22, 2012 at 11:17 PM, Jon Grant <jg-hus3n9K41k0@public.gmane.org> wrote:
> Hello
>
> Quoting from this page:
>
> http://man7.org/linux/man-pages/man3/errno.3.html
>
> "a function that succeeds is allowed to change errno."
>
> ^ This sounds clear, e.g. open() can change errno to 0, when it returns a
> valid fd handle.
>
>
> "Valid error numbers are all nonzero; errno is never set to zero by any
> system
>       call or library function."
>
> ^ This seems to be counter what the earlier line said. Therefore, open()
> wouldn't be allowed to change errno to 0.
>
> Have I missed something?

I don't really see the problem. The first part says functions may
change errno. The second part adds a qualification; they'll never
change it to zero.

Cheers,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface"; http://man7.org/tlpi/
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