Date: Sun, 06 Feb 2005 16:13:33 -0700 (MST) From: "M. Warner Losh" <imp@bsdimp.com> To: julian@lava.net Cc: dmw@unete.cl Subject: Re: [Hackers] Re: any way to reset errno? Message-ID: <20050206.161333.103235960.imp@bsdimp.com> In-Reply-To: <4206971F.1020005@lava.net> References: <20050206132124.GA746@daemon.unete.cl> <20050206.142319.22504831.imp@bsdimp.com> <4206971F.1020005@lava.net>
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In message: <4206971F.1020005@lava.net>
Julian Cowley <julian@lava.net> writes:
: M. Warner Losh wrote:
: > In message: <20050206132124.GA746@daemon.unete.cl>
: > Daniel Molina Wegener <dmw@unete.cl> writes:
: > : Any way to reset errno?
: >
: > errno = 0;
: >
: > Routines that return an error status in errno generally don't set it
: > to 0 to mean no error.
:
: Which implies errno should never need to be set to zero since the
: convention is to only look at errno if a system call fails. The only
: time errno needs to be explicitly set (to any value) is when preserving
: the error value between system calls. Such as:
:
: if (write(fd, buf, len) < 0) {
: int saved_errno;
:
: saved_errno = errno;
: close(fd); /* ignore any error */
: errno = saved_errno;
: return -1;
: }
Well, to portably[*] use some of the math(3) routines in libc, you
need to set it to 0 before calling them (strtol, et al come to mind).
Otherwise you are correct. In fact, it is generally incorrect to
write code like:
errno = 0;
close(fd);
if (errno != 0)
because errno isn't necessarily valid even if it has changed in that
case...
Warner
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