how to find out if a file exists?

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C++

Is there a portable way of finding out if a file exists?

Posted 2-Nov-11 9:29am

Joseph Marzbani

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Chuck O'Toole · Accepted Answer · 2011-11-02T09:36:00

Solution 2

Good Old fopen() does the trick

C

FILE *fp;
if ((fp = fopen((LPCTSTR)fName, "r")) == NULL)
{
  // file doesn't exist
}
else
{
  fclose(fp);
  // file does exist
}

(Updated)

If you're going to downvote the answer, at least have the courtesy to say why. Does "fopen()" not work? Of course it does, on all platforms, C and C++. The other solution points to a link that outlines several ways but require 3rd party (boost) or use functions that have different names for Windows and Linux (_access(), access()) which isn't "code transparent", meaning that you have to conditionalize the code for platform. If you're going to do that, you might as well use the platform specific calls and give up the idea of platform agnostic calls.

I'm not saying this is the "ideal" or "only" answer, I'm saying it answered the OPs question as posed and is not a "bad answer", maybe it's just one you don't like, but not wrong.

Posted 2-Nov-11 9:36am

Chuck O'Toole

Updated 2-Nov-11 14:43pm

v3

Comments

Albert Holguin 2-Nov-11 22:26pm

Countered downvote... This works, no reason to downvote... 5

Chuck O'Toole 2-Nov-11 22:34pm

Thanks

Sergey Alexandrovich Kryukov 3-Nov-11 0:24am

I up-voted the answer by my 5, what to discuss it.

This solution is reasonable, and your criticism of some other solutions is quite correct. I would say though that the argument "this works, that's why this is good" is generally insufficient (to my taste, bad non-working solution is much better than working bad solution), but you just don't need this argument.

I can easily imagine the motivation of the down-voter, some kind of false purism, like a predicate should not have a side effect. So, formally, you did not answer the question. But who says the question is reasonable? Who said that the solution of the problem "find out if the file exists, non-intrusively" has to be found? Your approach is good just because it suggests using of offensive programming instead of defensive, without any problems.

Domination of defensive programming really contaminates programming. I often saw such an idiotic code: if (!FileExists(fileName)) throw new Exception("File not found"); which is idiotic because a simple attempt to open this file (offensive) will throw quite relevant exception anyway, without any problems.

--SA

Chuck O'Toole 3-Nov-11 0:46am

Thanks SA. There are days when I do wear my "Master Software Engineer" hat (my actual job title) and defend architectural purity, especially when reviewing a new project proposal. However, I have a practical side which shows up when a reasonable answer is needed for an immediate problem. "Good because it works" is not a valid justification but "Rewrite it to be architecturally pure" is not a good response either. Especially when there is so little information about the application or the questioner's skills.

In this instance, the OP only wanted a portable way to check if a file existed. He didn't ask for a way without side effects (like actually opening the file). He didn't specify if he's using iostreams or standard IO or std:: io methods to manipulate the file. So, the simpliest, well known basic C functions that do the job was suggested. Now it's up to them to decide to use it or not or if the answer itself triggers some other idea for them.

Bala Selvanayagam 3-Nov-11 9:02am

Chuck,

I personally prefer your solution, I truely do not know why the OP has accepted my solution and it could be that your solution was not posted (time delay) when the OP looked at / some other valid reason from OP's point of view which we do not know?

my5 for your solution

Chuck O'Toole 3-Nov-11 9:22am

Thanks Bela. I actually liked your link as the dicsussion forum had several posts discussing the pros and cons of the methods outlined there. So, from a learning point of view, it was interesting.

I also want to make it clear that my complaint to the "person who downvoted" was not explicitly aimed at the OP as I have no way of knowing *who* downvoted it. It was more me yelling into the universe at large, hoping that whoever did that would respond.

Thanks to everyone for thier additions to this dicusssion and for their votes.

Bala Selvanayagam 3-Nov-11 9:58am

I understand Chuck,
:)

This has happened to me few times and know the feeling of working hard to give a solution and finally get downvoted and you would not know the reason & person.

some guys accidenlty downvote thinking that they are upvoting specially, if the are new to CP. Lower the downvote points its an accident.

Higher the downvote points, some one has done it purposely but if a genuine guy, should have reason for the downvote.

I do not normally downvote but if it has to then i give my little reason and its not me in this case :)

I strongly feel, if some one else's solution is better than my one then its better - i learn something every day and mine is a very tiny tiny contribution.

Bala Selvanayagam · Accepted Answer · 2011-11-02T09:35:00

Solution 1

http://stackoverflow.com/questions/268023/whats-the-best-way-to-check-if-a-file-exists-in-c-cross-platform[^]

Posted 2-Nov-11 9:35am

Bala Selvanayagam

Comments

Albert Holguin 2-Nov-11 22:29pm

Some of the suggestions listed in the link aren't that great... For example, if you're not using boost, no reason to use it just for this.

Bala Selvanayagam 3-Nov-11 8:59am

Albert,

Your commments makes sense and I personally prefer Chuck's solution, I truely do not know why the OP has accepted my solution and it could be that Chuck's solution was not posted (time delay) when the OP looked at / some other valid reason from OP's point of view which we do not know?

I really do not know & hope this is a constructive discussion.

May be ask the OP ?