Thread: problem appending

Yes, if you want to combine such attributes (e.g., ios::in | ios::out), but you cannot combine those two.

Originally Posted by Furious5k

But he said:

Yes, I said that - but I also said "Do not combine app with trunc" as you are at the same time saying "truncate the file" and "append to the file" - which makes absolutely no sense - and what you actually get from it is completely undefined.

What I wanted to tell is that IF you have valid combinations that you want to pass in, you need to combine them using the bitwise or operator.

Did you actually test if accfile is valid before writing to it? Such as

Code:

if (!accFile) {
    cout << "Could not open the file... " << endl;
    return;
}

It may well be that the iostream implementation actually detects the bad combination and the opening of the file fails, perhaps?

I am also a bit suspicious about this one:

Code:

       for (int i = 0; i < (BOOK_MAX+1); i++)

Why is there a +1 there?

--
Mats

--
Mats

Originally Posted by Furious5k

I tried to seperate them, like so, but it still didn't work (same segmentation fault).

The segmentation fault might have some other cause. For example, how many elements does Loans have?

Note that separating them the way you did just makes the first opening of the file have no net effect. You basically opened, did nothing, then closed.

Originally Posted by laserlight

Note that separating them the way you did just makes the first opening of the file have no net effect. You basically opened, did nothing, then closed.

Well, in the sequence as described here, it truncates the file, so it does indeed have an effect - it removes the conent in the file. Why you would THEN append to the file, I don't really understand, as there is no content to append onto - so the second file opening is absolutely meaningless waste of time [as long as the close is removed]. When the file is truncated, it has a zero length, the write (put) pointer is at the beginning of the file, and the file is opened for write - so what does the open with ios::app actually do at this point?

--
Mats

matsp - due to my lack of experience. I think it should be -1. An array[5] would be 0 to 4, yes?

Also, sorry for misreading.

laserlight - I was under the impression that opening the file with ios::trunc would erase its contents. How do I do this properly?


On another note, would this sort a "string myaray[NUMBER]" alphabetically?

Code:

#include <algorithm>
sort(myarray, myarray+NUMBER)

Originally Posted by Furious5k

laserlight - I was under the impression that opening the file with ios::trunc would erase its contents. How do I do this properly?

What are you trying to do?

Originally Posted by Furious5k

matsp - due to my lack of experience. I think it should be -1. An array[5] would be 0 to 4, yes?

That is probably causing your segmentation fault then - and it probably should be

Code:

for (int i = 0; i < BOOK_MAX; i++)

No +1 or -1.

Also, sorry for misreading.

laserlight - I was under the impression that opening the file with ios::trunc would erase its contents. How do I do this properly?

It does - but you do not then need to use ios::app on the file to add to it - since it is already empty.


On another note, would this sort a "string myaray[NUMBER]" alphabetically?

Code:

#include <algorithm>
sort(myarray, myarray+NUMBER)

[/QUOTE]

I suppose so.

--
Mats

Originally Posted by Furious5k

Does renaming a temporary file make it permanent?

No - all files are always permanent. Renaming a file changes it's name from one name to another. When I said temporary file, I meant something like "tmp.dat", and then rename it to "books.dat" or whatever the "real" name of the file is.

--
Mats

Originally Posted by Furious5k

It's working now. But when I cat the contents of the file I get the content I want plus a great many ";". I know which part of the code it is.

How would I tell the code to check for null value (never done it)?

Code:

if (Loans[i].Book = NULL)

That's how I understand it.

That is incorrect, it is checking

Code:

if ((Loans[i].Book = NULL) != 0)

, and since NULL == 0, it will never be true.

--
Mats