From:	horst DOT kraemer AT gmx DOT de (Horst Kraemer)
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: File Pointer.
Date:	Sat, 29 Apr 2000 09:25:40 GMT
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On Fri, 28 Apr 2000 08:06:26 GMT, hank_heng <hank_heng AT hotmail DOT com>
wrote:

>   If I have a File Pointer, how do I know I that file pointer is still
> pointing to a stream or it is already close ?

You cannot by just inspecting or acessing the pointer value. In fact
inspecting or acessing the pointer value of a FILE* after closing the
file already may induce undefined behaviour of the program.

Therefore it is mandatory to store this information in a separate
place - or to set the pointer variable to 0 before opening and after
closing a file.

	FILE*fp = 0;
        ...
        fp = fopen(...);
	...
	fclose(fp);
	fp=0;

But there may still be an inconsitency problem with this technique if
several pointer variables point to the same file. Therefore the only
safe technique would be a correct program design where you simply
"know" at any time if a specific file is open by recording this
knowledge in some separate variable which is acessible to the modules
which need this information.

Regards
Horst

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