ReadLine and Random Access

RE: ReadLine and Random Access

Danny
Since you are reading a line of text, you can keep track of how many characters you read. This will give you the position that you need. I haven't tried this myself, but it's worth a shot

Tu-Thac


----- Danny Smith wrote: ----

Hi

I need to read a file and be able to

1. Find the current position in the strea
2. Have access to a handy ReadLine() method

Obviously the FileStream class supports random access, so you have a Seek(
method and a Position property to find the current stream position, and th
StreamReader class has a ReadLine() method. I thought using these togethe
would give me what I needed

StreamReader sr = new StreamReader( File.OpenRead( filename ) )
string line = sr.ReadLine()
long position = sr.BaseStream.P osition

However, this does not work as the StreamReader has buffering which mean
the moment a Read call is made, much more than the single line is read fro
the BaseStream. Consequently the Position property does not return th
position *immediately* after the end of the line, which is what I need

This is possible in Java with the RandomAccessFil e class, which support
methods for reading lines and seeking / obtaining the position. Is ther
are way to do this in C#

One option would be to write my own ReadLine method which would allow me t
keep track of the stream position, but I'd like to know if there is a way t
avoid this

Can anyone help

Danny Smit

Re: ReadLine and Random Access

Hi Danny,

I've created a class that parses a file of records that may handle your
need. It maintains a file position, gives you random access to the records,
and maintains a record count. Can you tell me more about what you're doing
with the file? Are you breaking each line into fields? Can I get a sample of
your file?

Scott
scott_ctr_@_mod o_mail.com_ remove all the underscores to email me.
[color=blue]
> I need to read a file and be able to:
>
> 1. Find the current position in the stream
> 2. Have access to a handy ReadLine() method.[/color]

Re: ReadLine and Random Access

The only problem with that is that you don't know how many new-line
characters there are. Either one or two, depending on the file format, but
ReadLine() just returns the line and not these characters.

Danny

"Tu-Thach" <anonymous@disc ussions.microso ft.com> wrote in message
news:06F05ED4-6F48-421C-B145-9D8831A3B645@mi crosoft.com...[color=blue]
> Danny,
> Since you are reading a line of text, you can keep track of how many[/color]
characters you read. This will give you the position that you need. I
haven't tried this myself, but it's worth a shot.[color=blue]
>
> Tu-Thach
> www.ongtech.com
>
> ----- Danny Smith wrote: -----
>
> Hi,
>
> I need to read a file and be able to:
>
> 1. Find the current position in the stream
> 2. Have access to a handy ReadLine() method.
>
> Obviously the FileStream class supports random access, so you have a[/color]
Seek()[color=blue]
> method and a Position property to find the current stream position,[/color]
and the[color=blue]
> StreamReader class has a ReadLine() method. I thought using these[/color]
together[color=blue]
> would give me what I needed:
>
> StreamReader sr = new StreamReader( File.OpenRead( filename ) );
> string line = sr.ReadLine();
> long position = sr.BaseStream.P osition;
>
> However, this does not work as the StreamReader has buffering which[/color]
means[color=blue]
> the moment a Read call is made, much more than the single line is[/color]
read from[color=blue]
> the BaseStream. Consequently the Position property does not return[/color]
the[color=blue]
> position *immediately* after the end of the line, which is what I[/color]
need.[color=blue]
>
> This is possible in Java with the RandomAccessFil e class, which[/color]
supports[color=blue]
> methods for reading lines and seeking / obtaining the position. Is[/color]
there[color=blue]
> are way to do this in C#?
>
> One option would be to write my own ReadLine method which would allow[/color]
me to[color=blue]
> keep track of the stream position, but I'd like to know if there is a[/color]
way to[color=blue]
> avoid this.
>
> Can anyone help?
>
> Danny Smith
>
>
>[/color]

Re: ReadLine and Random Access

Scott,

The file is a pdf file. Some of the file needs to be read as bytes as it is
not text, yet certain parts are more conveniently read as lines of text. I
would like to be able to:

1. Jump to a known position in the stream, position X
2. Read a line of text
3. Read some bytes.
4. Jump a few bytes back in the stream, position X + y.

The only unknown in this is the number new-line characters the line of text
has, but this means that I cannot work out the value of y.

Possibly I could read the line as bytes, then I would know exactly how many
bytes it was. I just wondered if there was a slightly easier way, as after
reading a line in Java you could query the stream for the exact position, so
I thought there may be something I'm unaware of in C#.

This would also be handy if you were reading in lines of text from a large
file (with an unknown number of lines) and you wanted to display a progress
bar showing how much of the file had been read. If you could get the
current position in the stream you could then calculate the percentage read
using the stream length. How would you do this?

Thanks,

Danny


"Scott" <me@me.com> wrote in message
news:%23bakYy89 DHA.2168@TK2MSF TNGP12.phx.gbl. ..[color=blue]
> Hi Danny,
>
> I've created a class that parses a file of records that may handle your
> need. It maintains a file position, gives you random access to the[/color]
records,[color=blue]
> and maintains a record count. Can you tell me more about what you're doing
> with the file? Are you breaking each line into fields? Can I get a sample[/color]
of[color=blue]
> your file?
>
> Scott
> scott_ctr_@_mod o_mail.com_ remove all the underscores to email me.
>[color=green]
> > I need to read a file and be able to:
> >
> > 1. Find the current position in the stream
> > 2. Have access to a handy ReadLine() method.[/color]
>
>[/color]

Re: ReadLine and Random Access

You can get the length of the string you just read. Seek to that location, read 1 or 2 characters to determine whether it is \n or \r\n. Then, add the appropriate count to your length

Tu-Thac


----- Danny Smith wrote: ----

The only problem with that is that you don't know how many new-lin
characters there are. Either one or two, depending on the file format, bu
ReadLine() just returns the line and not these characters

Dann

"Tu-Thach" <anonymous@disc ussions.microso ft.com> wrote in messag
news:06F05ED4-6F48-421C-B145-9D8831A3B645@mi crosoft.com..[color=blue]
> Danny
> Since you are reading a line of text, you can keep track of how man[/color]
characters you read. This will give you the position that you need.
haven't tried this myself, but it's worth a shot[color=blue][color=green]
>> Tu-Thac[/color]
> www.ongtech.co[color=green]
>> ----- Danny Smith wrote: ----
>> Hi
>> I need to read a file and be able to
>> 1. Find the current position in the strea[/color]
> 2. Have access to a handy ReadLine() method[color=green]
>> Obviously the FileStream class supports random access, so you have[/color][/color]
Seek([color=blue]
> method and a Position property to find the current stream position[/color]
and th[color=blue]
> StreamReader class has a ReadLine() method. I thought using thes[/color]
togethe[color=blue]
> would give me what I needed[color=green]
>> StreamReader sr = new StreamReader( File.OpenRead( filename ) )[/color]
> string line = sr.ReadLine()
> long position = sr.BaseStream.P osition[color=green]
>> However, this does not work as the StreamReader has buffering whic[/color][/color]
mean[color=blue]
> the moment a Read call is made, much more than the single line i[/color]
read fro[color=blue]
> the BaseStream. Consequently the Position property does not retur[/color]
th[color=blue]
> position *immediately* after the end of the line, which is what[/color]
need[color=blue][color=green]
>> This is possible in Java with the RandomAccessFil e class, whic[/color][/color]
support[color=blue]
> methods for reading lines and seeking / obtaining the position. I[/color]
ther[color=blue]
> are way to do this in C#[color=green]
>> One option would be to write my own ReadLine method which would allo[/color][/color]
me t[color=blue]
> keep track of the stream position, but I'd like to know if there is[/color]
way t[color=blue]
> avoid this[color=green]
>> Can anyone help
>> Danny Smit[color=darkred]
>>>[/color][/color][/color]

Re: ReadLine and Random Access

Unfortunately, my parser isn't up to this task either. Since you're mixing
binary and text, I think your best bet would be to derive your own class
from FileStream that adds a ReadLine method. You can look at the
implementation of StreamReader
(http://www.123aspx.com/rotor/rotorsrc.aspx?rot=42055) to help with
implementing the ReadLine method. This should be a fairly simple job.

Scott
[color=blue]
> The file is a pdf file. Some of the file needs to be read as bytes as it[/color]
is[color=blue]
> not text, yet certain parts are more conveniently read as lines of text.[/color]
I[color=blue]
> would like to be able to:
>
> 1. Jump to a known position in the stream, position X
> 2. Read a line of text
> 3. Read some bytes.
> 4. Jump a few bytes back in the stream, position X + y.
>
> The only unknown in this is the number new-line characters the line of[/color]
text[color=blue]
> has, but this means that I cannot work out the value of y.
>
> Possibly I could read the line as bytes, then I would know exactly how[/color]
many[color=blue]
> bytes it was. I just wondered if there was a slightly easier way, as[/color]
after[color=blue]
> reading a line in Java you could query the stream for the exact position,[/color]
so[color=blue]
> I thought there may be something I'm unaware of in C#.
>
> This would also be handy if you were reading in lines of text from a large
> file (with an unknown number of lines) and you wanted to display a[/color]
progress[color=blue]
> bar showing how much of the file had been read. If you could get the
> current position in the stream you could then calculate the percentage[/color]
read[color=blue]
> using the stream length. How would you do this?[/color]

Re: ReadLine and Random Access

Unfortunately, my parser isn't up to this task either. Since you're mixing
binary and text, I think your best bet would be to derive your own class
from FileStream that adds a ReadLine method. You can look at the
implementation of StreamReader
(http://www.123aspx.com/rotor/rotorsrc.aspx?rot=42055) to help with
implementing the ReadLine method. This should be a fairly simple job.

Scott
[color=blue]
> The file is a pdf file. Some of the file needs to be read as bytes as it[/color]
is[color=blue]
> not text, yet certain parts are more conveniently read as lines of text.[/color]
I[color=blue]
> would like to be able to:
>
> 1. Jump to a known position in the stream, position X
> 2. Read a line of text
> 3. Read some bytes.
> 4. Jump a few bytes back in the stream, position X + y.
>
> The only unknown in this is the number new-line characters the line of[/color]
text[color=blue]
> has, but this means that I cannot work out the value of y.
>
> Possibly I could read the line as bytes, then I would know exactly how[/color]
many[color=blue]
> bytes it was. I just wondered if there was a slightly easier way, as[/color]
after[color=blue]
> reading a line in Java you could query the stream for the exact position,[/color]
so[color=blue]
> I thought there may be something I'm unaware of in C#.
>
> This would also be handy if you were reading in lines of text from a large
> file (with an unknown number of lines) and you wanted to display a[/color]
progress[color=blue]
> bar showing how much of the file had been read. If you could get the
> current position in the stream you could then calculate the percentage[/color]
read[color=blue]
> using the stream length. How would you do this?[/color]

Re: ReadLine and Random Access

Scott,

That's exactly what I will do then! Thanks very much for that link - I
would not have known where to find that code!

Danny


"Scott" <me@me.com> wrote in message
news:uAweIG$9DH A.548@TK2MSFTNG P11.phx.gbl...[color=blue]
> Unfortunately, my parser isn't up to this task either. Since you're mixing
> binary and text, I think your best bet would be to derive your own class
> from FileStream that adds a ReadLine method. You can look at the
> implementation of StreamReader
> (http://www.123aspx.com/rotor/rotorsrc.aspx?rot=42055) to help with
> implementing the ReadLine method. This should be a fairly simple job.
>
> Scott
>[color=green]
> > The file is a pdf file. Some of the file needs to be read as bytes as[/color][/color]
it[color=blue]
> is[color=green]
> > not text, yet certain parts are more conveniently read as lines of text.[/color]
> I[color=green]
> > would like to be able to:
> >
> > 1. Jump to a known position in the stream, position X
> > 2. Read a line of text
> > 3. Read some bytes.
> > 4. Jump a few bytes back in the stream, position X + y.
> >
> > The only unknown in this is the number new-line characters the line of[/color]
> text[color=green]
> > has, but this means that I cannot work out the value of y.
> >
> > Possibly I could read the line as bytes, then I would know exactly how[/color]
> many[color=green]
> > bytes it was. I just wondered if there was a slightly easier way, as[/color]
> after[color=green]
> > reading a line in Java you could query the stream for the exact[/color][/color]
position,[color=blue]
> so[color=green]
> > I thought there may be something I'm unaware of in C#.
> >
> > This would also be handy if you were reading in lines of text from a[/color][/color]
large[color=blue][color=green]
> > file (with an unknown number of lines) and you wanted to display a[/color]
> progress[color=green]
> > bar showing how much of the file had been read. If you could get the
> > current position in the stream you could then calculate the percentage[/color]
> read[color=green]
> > using the stream length. How would you do this?[/color]
>
>[/color]