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Date: Fri, 07 Feb 2014 18:38:58 -0500
From: "Larry Hall (Cygwin)" <reply-to-list-only-lh@cygwin.com>
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Subject: Re: get rid of getpwent? (Was: cygwin-1.7.28 getpwent header declaration changes ?)
References: <52F339CA.5070305@gmail.com> <20140206090117.GD2821@calimero.vinschen.de> <52F361C5.3000807@gmail.com> <20140206141321.GI2821@calimero.vinschen.de> <52F40208.5030901@etr-usa.com> <20140207094917.GN2821@calimero.vinschen.de> <52F53D7C.5050201@etr-usa.com> <52F553AA.9090500@cygwin.com> <52F561EE.8090806@tiscali.co.uk>
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On 2/7/2014 5:45 PM, David Stacey wrote:
> On 07/02/14 21:44, Larry Hall (Cygwin) wrote:
>> On 2/7/2014 3:09 PM, Warren Young wrote:
>>> This takes 7.1 seconds on my system, with a 12-line /etc/passwd file:
>>>
>>>       #include <pwd.h>
>>>       #include <stdio.h>
>>>       #include <stdlib.h>
>>>
>>>       int main(int argc, const char* argv[])
>>>       {
>>>           int i;
>>>           const char* user = argv[1];
>>>
>>>           if (!user) {
>>>               printf("usage: %s username\n", argv[0]);
>>>               exit(1);
>>>           }
>>>
>>>           for (i = 0; i < 1000000; ++i) {
>>>               struct passwd* pw = getpwnam(user);
>>>               if (!pw) {
>>>                   printf("User %s doesn't exist!\n", user);
>>>                   exit(2);
>>>               }
>>>               else if (i == 0) {
>>>                   printf("User %s is UID %d\n", user, pw->pw_uid);
>>>               }
>>>           }
>>>       }
>>>
>>> So, each getpwnam() call takes 7.1 microseconds on average.
>>
>> I think you forgot to put an "exit(0);" after the last printf(). Without
>> it, you're checking for the same user a million times, which is certainly
>> going to take a little time. ;-)
>>
>
> I thought the point of the programme /was/ to call getpwnam() a million
> times. Time this as accurately as you can. Then, with a quick division, you
> get the time for one call.

Hm, I missed that he summarized with _microseconds_, even though I quoted
that too in my response. :-(

My average was much closer to 2 microseconds per call but that could be
machine differences.

In any case, sorry for the noise.

-- 
Larry

_____________________________________________________________________

A: Yes.
 > Q: Are you sure?
 >> A: Because it reverses the logical flow of conversation.
 >>> Q: Why is top posting annoying in email?

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