seeekg/tellg not working properly?

[Randy Yates]

I'm using mingw/g++ 3.3.3. When I use pos = tellg(), getline(), setg(pos), then
the next getline() does NOT get from the original position. I've tried doing
a clear() before the seekg() to no avail. In essence I've made my own "GetLine"
and "PeekLine" functions for my class but due to this problem its not working
properly

void BOOK::GetLine(s tring &line)
{
char linechar[MAX_LINE_SIZE];

line.erase();
inpFile.getline (linechar, MAX_LINE_SIZE);
line.assign(lin echar);
lineNo++;
};

void BOOK::PeekLine( string &line)
{
char linechar[MAX_LINE_SIZE];
streampos startPos;

startPos = inpFile.tellg() ;
inpFile.getline (linechar, MAX_LINE_SIZE);
line.erase();
line.assign(lin echar);
inpFile.seekg(s tartPos);
};

Am I doing something stupid, or am I justified in getting pissed off? This should
have taken about 30 seconds to code and test instead of 1hour+.
--
% Randy Yates % "Ticket to the moon, flight leaves here today
%% Fuquay-Varina, NC % from Satellite 2"
%%% 919-577-9882 % 'Ticket To The Moon'
%%%% <ya***@ieee.org > % *Time*, Electric Light Orchestra
http://home.earthlink.net/~yatescr

[Unforgiven]

"Randy Yates" <ya***@ieee.org > wrote in message
news:ac******** **@ieee.org...

I'm using mingw/g++ 3.3.3. When I use pos = tellg(), getline(), setg(pos),
then
the next getline() does NOT get from the original position. I've tried
doing
a clear() before the seekg() to no avail. In essence I've made my own
"GetLine"
and "PeekLine" functions for my class but due to this problem its not
working
properly

inpFile.seekg(s tartPos);

How's about using:
inpFile.seekg(s tartPos, ios_base::beg);

--
Unforgiven

[Randy Yates]

"Unforgiven " <ja*******@hotm ail.com> writes:

"Randy Yates" <ya***@ieee.org > wrote in message
news:ac******** **@ieee.org...

I'm using mingw/g++ 3.3.3. When I use pos = tellg(), getline(), setg(pos),
then
the next getline() does NOT get from the original position. I've tried
doing
a clear() before the seekg() to no avail. In essence I've made my own
"GetLine"
and "PeekLine" functions for my class but due to this problem its not
working
properly

inpFile.seekg(s tartPos);
How's about using:
inpFile.seekg(s tartPos, ios_base::beg);

Thanks, but still no joy.
--
Unforgiven

Metallica?
--
% Randy Yates % "With time with what you've learned,
%% Fuquay-Varina, NC % they'll kiss the ground you walk
%%% 919-577-9882 % upon."
%%%% <ya***@ieee.org > % '21st Century Man', *Time*, ELO
http://home.earthlink.net/~yatescr

[Randy Yates]

Randy Yates <ya***@ieee.org > writes:

"Unforgiven " <ja*******@hotm ail.com> writes:

"Randy Yates" <ya***@ieee.org > wrote in message
news:ac******** **@ieee.org...

I'm using mingw/g++ 3.3.3. When I use pos = tellg(), getline(), setg(pos),
then
the next getline() does NOT get from the original position. I've tried
doing
a clear() before the seekg() to no avail. In essence I've made my own
"GetLine"
and "PeekLine" functions for my class but due to this problem its not
working
properly

inpFile.seekg(s tartPos);

How's about using:
inpFile.seekg(s tartPos, ios_base::beg);

Thanks, but still no joy.

I have found since posting that this is apparently a bug in gcc. See gcc bug #13333.
--
% Randy Yates % "Watching all the days go by...
%% Fuquay-Varina, NC % Who are you and who am I?"
%%% 919-577-9882 % 'Mission (A World Record)',
%%%% <ya***@ieee.org > % *A New World Record*, ELO
http://home.earthlink.net/~yatescr

[Malte Starostik]

Randy Yates schrieb:

void BOOK::GetLine(s tring &line)
{
char linechar[MAX_LINE_SIZE];

line.erase();
inpFile.getline (linechar, MAX_LINE_SIZE);
line.assign(lin echar);
lineNo++;
};

FWIW, there's std::getline that takes a std::string as an argument, no
need for hardcoded length limits and a char array:

using namespace std;

void BOOK::GetLine(s tring &line)
{
getline(inpFile , line);
++lineNo;
}

Regards,
Malte

[Randy Yates]

Malte Starostik <ma************ *@t-online.de> writes:

Randy Yates schrieb:

void BOOK::GetLine(s tring &line)
{
char linechar[MAX_LINE_SIZE];
line.erase();
inpFile.getline (linechar, MAX_LINE_SIZE);
line.assign(lin echar);
lineNo++;
};

FWIW, there's std::getline that takes a std::string as an argument, no
need for hardcoded length limits and a char array:

using namespace std;

void BOOK::GetLine(s tring &line)
{
getline(inpFile , line);
++lineNo;
}

Regards,
Malte

Thanks Malte, I'll keep that possibility in mind.
--
% Randy Yates % "And all that I can do
%% Fuquay-Varina, NC % is say I'm sorry,
%%% 919-577-9882 % that's the way it goes..."
%%%% <ya***@ieee.org > % Getting To The Point', *Balance of Power*, ELO
http://home.earthlink.net/~yatescr

[Mike Wahler]

"Randy Yates" <ya***@ieee.org > wrote in message
news:8y******** **@ieee.org...

Malte Starostik <ma************ *@t-online.de> writes:

Randy Yates schrieb:

void BOOK::GetLine(s tring &line)
{
char linechar[MAX_LINE_SIZE];
line.erase();
inpFile.getline (linechar, MAX_LINE_SIZE);
line.assign(lin echar);
lineNo++;
};

FWIW, there's std::getline that takes a std::string as an argument, no
need for hardcoded length limits and a char array:

using namespace std;

void BOOK::GetLine(s tring &line)
{
getline(inpFile , line);
++lineNo;
}

Regards,
Malte

Thanks Malte, I'll keep that possibility in mind.

But note that 'getline()' depends upon newline characters,
which can require translation (via a 'text mode' stream)(*),
and that in 'text mode', 'seek()' and 'tell()' functions
can never be guaranteed to have a byte-level precision.

(*) Some platforms externally represent '\n' with more than
a single character. In the C++ memory model, '\n' is
always a single character. (Ain't I/O fun? :-) )

-Mike

[John Harrison]

"Randy Yates" <ya***@ieee.org > wrote in message
news:ac******** **@ieee.org...

I'm using mingw/g++ 3.3.3. When I use pos = tellg(), getline(), setg(pos),
then
the next getline() does NOT get from the original position. I've tried
doing
a clear() before the seekg() to no avail. In essence I've made my own
"GetLine"
and "PeekLine" functions for my class but due to this problem its not
working
properly

void BOOK::GetLine(s tring &line)
{
char linechar[MAX_LINE_SIZE];

line.erase();
inpFile.getline (linechar, MAX_LINE_SIZE);
line.assign(lin echar);
lineNo++;
};

void BOOK::PeekLine( string &line)
{
char linechar[MAX_LINE_SIZE];
streampos startPos;

startPos = inpFile.tellg() ;
inpFile.getline (linechar, MAX_LINE_SIZE);
line.erase();
line.assign(lin echar);
inpFile.seekg(s tartPos);
};

Am I doing something stupid, or am I justified in getting pissed off? This
should
have taken about 30 seconds to code and test instead of 1hour+.

There's nothing I can see wrong with the code above. At least nothing
relevant to the problem you are describing. The problem is somewhere in the
code you didn't post.

If you can post a complete program that demonstrates this problem then
you'll get whatever it is sorted out very quickly.

Doing a clear() before the seekg() is a good idea however. It will make your
function work when the getline() happens to cause an end of file condition.

john

[Catalin Pitis]

"Mike Wahler" <mk******@mkwah ler.net> wrote in message
news:aN******** *********@newsr ead3.news.pas.e arthlink.net...

"Randy Yates" <ya***@ieee.org > wrote in message
news:8y******** **@ieee.org...

Malte Starostik <ma************ *@t-online.de> writes:

> Randy Yates schrieb:
>> void BOOK::GetLine(s tring &line)
>> {
>> char linechar[MAX_LINE_SIZE];
>> line.erase();
>> inpFile.getline (linechar, MAX_LINE_SIZE);
>> line.assign(lin echar);
>> lineNo++;
>> };
>
> FWIW, there's std::getline that takes a std::string as an argument, no
> need for hardcoded length limits and a char array:
>
> using namespace std;
>
> void BOOK::GetLine(s tring &line)
> {
> getline(inpFile , line);
> ++lineNo;
> }
>
> Regards,
> Malte

Thanks Malte, I'll keep that possibility in mind.

But note that 'getline()' depends upon newline characters,
which can require translation (via a 'text mode' stream)(*),
and that in 'text mode', 'seek()' and 'tell()' functions
can never be guaranteed to have a byte-level precision.

(*) Some platforms externally represent '\n' with more than
a single character. In the C++ memory model, '\n' is
always a single character. (Ain't I/O fun? :-) )

I had that problem once. I solved it by using the "extended" overload of
getline. I opened the input stream as binary stream and I explicitly
specified the eol character ('\x0A'). For what I had to solve, it was ok.

Catalin