file opening errors

[Alan]

How can I get detailed information on WHY an error occurs upon
attempt to open? I know how to use the member function ".good()" but
cannot find how to get information on why it failed to open.

[Ney André de Mello Zunino]

Re: file opening errors

Alan wrote:
[color=blue]
> How can I get detailed information on WHY an error occurs upon
> attempt to open? I know how to use the member function ".good()" but
> cannot find how to get information on why it failed to open.[/color]

AFAICT, the standard language will only allow you to test whether the
stream is ready/good to be used or not. "Detailed information", such as
whether the file operation failed because of lack of permission, etc.
would have to be obtained from the OS, with OS-specific calls. Then
again, I could be missing something.

Regards,

--
Ney André de Mello Zunino

[Alan]

Re: file opening errors

Here is more about what is happending. The following code produces an
error on a file "test1.txt" , the second time through the "for" loop.
The errors printed out are:

File failure
Reached end of file

Any ideas? Thanks, Alan

Code:

opts.filter = "test*.txt" ;
FindFile find(opts);
find.search();
nfiles = (int) find.filelist.s ize();

for (int i = 0; i < nfiles; i++)
{
string fullname = FindFile::combi nePath(find.fil elist[i].path,
find.filelist[i].fileinfo.cFile Name);
infile.open(ful lname.c_str());

if (infile.good()& &outfile.good() )
while (getline(infile ,in_string,'\n' ))
{
. . .
}
else
{
if (!infile.good() ) cout << "*** Unable to read input
file ***\n";
else cout << "*** Unable to read output file ***\n";
if (infile.bad()) cout << "Reading error\n";
if (infile.fail()) cout << "File failure\n";
if (infile.eof()) cout << "Reached end of file\n";
}
infile.close();
}

[Panjandrum]

Re: file opening errors

Alan wrote:[color=blue]
> How can I get detailed information on WHY an error occurs upon
> attempt to open? I know how to use the member function ".good()" but
> cannot find how to get information on why it failed to open.[/color]

If you used fopen ...

perror ();
strerror (errno);

[Larry I Smith]

Re: file opening errors

Alan wrote:[color=blue]
> Here is more about what is happending. The following code produces an
> error on a file "test1.txt" , the second time through the "for" loop.
> The errors printed out are:
>
> File failure
> Reached end of file
>
> Any ideas? Thanks, Alan
>
> Code:
>
> opts.filter = "test*.txt" ;
> FindFile find(opts);
> find.search();
> nfiles = (int) find.filelist.s ize();
>
> for (int i = 0; i < nfiles; i++)
> {
> string fullname = FindFile::combi nePath(find.fil elist[i].path,
> find.filelist[i].fileinfo.cFile Name);
> infile.open(ful lname.c_str());
>
> if (infile.good()& &outfile.good() )
> while (getline(infile ,in_string,'\n' ))
> {
> . . .
> }
> else
> {
> if (!infile.good() ) cout << "*** Unable to read input
> file ***\n";
> else cout << "*** Unable to read output file ***\n";
> if (infile.bad()) cout << "Reading error\n";
> if (infile.fail()) cout << "File failure\n";
> if (infile.eof()) cout << "Reached end of file\n";
> }
> infile.close();[/color]


infile.clear(); // clear EOF & error flags
[color=blue]
> }
>[/color]

[Alan]

Re: file opening errors

Larry: Thanks. This did it. Alan
[color=blue]
> infile.clear(); // clear EOF & error flags
>[/color]

[Jack Klein]

Re: file opening errors

On 19 Jun 2005 14:13:56 -0700, "Panjandrum " <pan6c7yc0j@spa mbob.com>
wrote in comp.lang.c++:
[color=blue]
> Alan wrote:[color=green]
> > How can I get detailed information on WHY an error occurs upon
> > attempt to open? I know how to use the member function ".good()" but
> > cannot find how to get information on why it failed to open.[/color]
>
> If you used fopen ...
>
> perror ();
> strerror (errno);[/color]

Neither the C nor C++ standards require that the standard library
function fopen() set errno on a failure. Your implementation might do
so, but that is a non-standard extension and code using it will not be
portable.

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.l earn.c-c++

http://www.contrib.andrew.cmu.edu/~ajo/docs/FAQ-acllc.html

[Panjandrum]

Re: file opening errors

Jack Klein wrote:[color=blue]
> "Panjandrum " wrote in comp.lang.c++:[color=green]
> > If you used fopen ...
> >
> > perror ();
> > strerror (errno);[/color]
>
> Neither the C nor C++ standards require that the standard library
> function fopen() set errno on a failure. Your implementation might do
> so, but that is a non-standard extension and code using it will not be
> portable.[/color]

You portably get the last system error message. Nothing more, nothing
less.