fstream::open problem

[Belebele]

The code below does not cause an assertion failure.

fstream f;
f.open("myfile" );
assert( f.is_open() );



However, the one below does fail the assert:

fstream f;
f.open("myfile" , ios::in | ios::out | ios::app);
assert( f.is_open() );


Any idea why?


Thanks:
Belebele

[Victor Bazarov]

Re: fstream::open problem

Belebele wrote:

The code below does not cause an assertion failure.
>
fstream f;
f.open("myfile" );
assert( f.is_open() );
>
>
>
However, the one below does fail the assert:
>
fstream f;
f.open("myfile" , ios::in | ios::out | ios::app);
assert( f.is_open() );
>
>
Any idea why?

'ios::app' cannot be combined with 'ios::in' (27.8.1.3/2).

V
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[Belebele]

Re: fstream::open problem


Victor Bazarov wrote:

'ios::app' cannot be combined with 'ios::in' (27.8.1.3/2).

Does that mean that I cannot read from the file if I want to append?
Will I retain the capability to read from the file if I remove ios::in?

Also, what does the numbers mean at the end of your line mean? Some
link into a document somewhere? (I have looked in many places ...)

Thanks:

AQ

[Victor Bazarov]

Re: fstream::open problem

Belebele wrote:

Victor Bazarov wrote:

>'ios::app' cannot be combined with 'ios::in' (27.8.1.3/2).

>
Does that mean that I cannot read from the file if I want to append?

No, you just can't rely on the appending capabilities of the streams
if you want to be reading from the same file.

Will I retain the capability to read from the file if I remove
ios::in?

No. I suggest you just use 'in' and 'out', and perform positioning
of the stream yourself.

Also, what does the numbers mean at the end of your line mean? Some
link into a document somewhere? (I have looked in many places ...)

They are the chapter[.section[.subsection]]/paragraph of the Standard.
If you want to get a copy, see the FAQ where to get it.

V
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