file open modes

[Sherak]

Hi

Does anyone know the the correct file open mode to replace a line in a stream. ios::????

ie I have a file like so:

one
two
three
four

and I want to replace one with a diferent string ?..

regards,

 

[2ffat]

I'm assumming that you want to open the file for both input and output. Therefore, you need to use fstream instead of ofstream or ifstream. I assume you've already guessed that since now you want to use ios manipulators. If you use

ios::out

without another manipulator, the file will open for truncation. (The same as

ios::trunc

.) Have you tried just

ios::in|ios::out

?

You could do try

ios::in|ios::app

or

ios::in|ios::out|ios::ate

. I haven't tried just the

ios::ate

by itself but it might work, too.

The ios::app opens an output file for appending only. Ios::ate opens a file (input or output) for appending. Both seek to the end of the file so you will have to position to the beginning of the file to do any kind of search.

One thing to note: if you don't declare standard namespace, you may have to use

std::ios::in|std::ios::out[\code], etc.

Bruce Eckel is working on a revision to his book [i]Thinking in C++[/i]. You can download a rought draft at [URL unfurl="true"]http://64.78.49.204/[/URL] . It talks about IOStreams in it.

James P. Cottingham
[COLOR=blue]
When a man sits with a pretty girl for an hour, it seems like a minute. But let him sit on a hot stove for a minute and it's longer than any hour. That's relativity.
[/color][tab][tab]Albert Einstein explaining his Theory of Relativity to a group of journalists.

 

[Sherak]

Thanks for the reply,

Yes I've tried all those handles, they all seem to either add to the end, insert or delete the contents of the file. Thanks for the link on the book though, also I'll try the namespace way.

Thanks again.

 

[Totte]

If i'm not mistaking your problem is that you has a file with strings in and want to replace any given string with another one.......
If that is the case you must know that the strings are "packed" like this: "one\rtwo\rtree\rfour\r" or whatever character in between. This means that it's not just indexing and writing a new string with a DIFFERENT length, if the lengths are equal it's ok (i.e "one\r" -> "One\r" is OK, "one\r"->"Twelve\r" is trouble).
This means that in case SOME or all of the strings can differ i length You need to read, change and save in another file, and when all is done, delete the original file and rename the new to the same name.

Totte