Reading a file from a specified range

[mkarja]

Hi,

I'm trying to figure out how to read some range of rows from a
file.
Is it possible to search the file with some criteria and then
when the search string is found read 3 rows before and after
that row from where the search string was found ?
Of course the row where the string was found should also be read.

I have a log file in txt format. I need to read the file if
there's any errors. There's two lines that has error information
if something goes wrong. I need to get the errors and the command
that caused the error which is about three rows above the first
error line. I have to use the error as a search string because
the command changes everytime so I can't use the command as a
search string.

The error lines are as follows:
/*** SYNTAX ERROR ***/
/*** INVALID PARAMETER NAME ***/

I'm using /*** as a search string.
I could use seekg if I just needed to read the file forward from
the point where the search string was found, but I can't figure
how I could do what I'm trying to do here.

I hope you understand what I'm trying to do here. If not, I'll
try to explain more.

----
mkarja

[John Harrison]

"mkarja" <mm**********@h otmail.com> wrote in message
news:75******** *************** ***@posting.goo gle.com...

Hi,

I'm trying to figure out how to read some range of rows from a
file.
Is it possible to search the file with some criteria and then
when the search string is found read 3 rows before and after
that row from where the search string was found ?
Of course the row where the string was found should also be read.

The problem is the reading backwards bit. Instead of trying to do this you
should keep the last three lines read in memory somewhere so that when you
do find the string you are looking for you have all the information you
need.

Something like this

string last_three_line s[3];
string curr_line;
while (getline(file, curr_line))
{
if (current line is error line)
{
...
}
last_three_line s[0] = last_three_line s[1];
last_three_line s[1] = last_three_line s[2];
last_three_line s[2] = curr_line;
}

john

[Chris \( Val \)]

"mkarja" <mm**********@h otmail.com> wrote in message
news:75******** *************** ***@posting.goo gle.com...
| Hi,
|
| I'm trying to figure out how to read some range of rows from a
| file.
| Is it possible to search the file with some criteria and then
| when the search string is found read 3 rows before and after
| that row from where the search string was found ?
| Of course the row where the string was found should also be read.
|
| I have a log file in txt format. I need to read the file if
| there's any errors. There's two lines that has error information
| if something goes wrong. I need to get the errors and the command
| that caused the error which is about three rows above the first
| error line. I have to use the error as a search string because
| the command changes everytime so I can't use the command as a
| search string.
|
| The error lines are as follows:
| /*** SYNTAX ERROR ***/
| /*** INVALID PARAMETER NAME ***/
|
| I'm using /*** as a search string.
| I could use seekg if I just needed to read the file forward from
| the point where the search string was found, but I can't figure
| how I could do what I'm trying to do here.
|
| I hope you understand what I'm trying to do here. If not, I'll
| try to explain more.

You can *seek* backwards, in the same way that
you can seek *forward* to obtain an reasonable
result:

// Approx line size in the file...
std::ifstream:: pos_type OneLine( 100 );

// Seek backwards from the current position
// in the stream...
InFile.seekg( -OneLine, std::ios_base:: cur );

....then:

while( std::getline( InFile, Buffer ) )
// ...

Cheers.
Chris Val

[David Rubin]

"Chris \( Val \)" <ch******@bigpo nd.com.au> wrote in message news:<2t******* ******@uni-berlin.de>...

"mkarja" <mm**********@h otmail.com> wrote in message
news:75******** *************** ***@posting.goo gle.com... | I have a log file in txt format. I need to read the file if
| there's any errors. There's two lines that has error information
| if something goes wrong. I need to get the errors and the command
| that caused the error which is about three rows above the first
| error line. I have to use the error as a search string because
| the command changes everytime so I can't use the command as a
| search string.
[snip] You can *seek* backwards, in the same way that
you can seek *forward* to obtain an reasonable
result:

// Approx line size in the file...
std::ifstream:: pos_type OneLine( 100 );

// Seek backwards from the current position
// in the stream...
InFile.seekg( -OneLine, std::ios_base:: cur );

...then:

while( std::getline( InFile, Buffer ) )
// ...

The typical solution is to read lines into a circular buffer with the
minimum capacity necessary. This seems to be 5 in your case: 2 lines
of interest, plus the 3 previous lines.

/david

[Chris \( Val \)]

"David Rubin" <da********@war pmail.net> wrote in message
news:82******** *************** *@posting.googl e.com...
| "Chris \( Val \)" <ch******@bigpo nd.com.au> wrote in message
news:<2t******* ******@uni-berlin.de>...
| > "mkarja" <mm**********@h otmail.com> wrote in message
| > news:75******** *************** ***@posting.goo gle.com...
|
| > | I have a log file in txt format. I need to read the file if
| > | there's any errors. There's two lines that has error information
| > | if something goes wrong. I need to get the errors and the command
| > | that caused the error which is about three rows above the first
| > | error line. I have to use the error as a search string because
| > | the command changes everytime so I can't use the command as a
| > | search string.
|
| [snip]
| > You can *seek* backwards, in the same way that
| > you can seek *forward* to obtain an reasonable
| > result:
| >
| > // Approx line size in the file...
| > std::ifstream:: pos_type OneLine( 100 );
| >
| > // Seek backwards from the current position
| > // in the stream...
| > InFile.seekg( -OneLine, std::ios_base:: cur );
| >
| > ...then:
| >
| > while( std::getline( InFile, Buffer ) )
| > // ...
|
| The typical solution is to read lines into a circular buffer with the
| minimum capacity necessary. This seems to be 5 in your case: 2 lines
| of interest, plus the 3 previous lines.

Yes, of course :-)

I thought it was pretty clear from the above
that one would therefore write something like:

std::ifstream:: pos_type Previous( OneLine * 3 );
InFile.seekg( -Previous, std::ios_base:: cur );

// Read '5' lines into an buffer, or deal with
// each one individually...

Cheers.
Chris Val

[mkarja]

> Yes, of course :-)

I thought it was pretty clear from the above
that one would therefore write something like:

std::ifstream:: pos_type Previous( OneLine * 3 );
InFile.seekg( -Previous, std::ios_base:: cur );

// Read '5' lines into an buffer, or deal with
// each one individually...

Cheers.
Chris Val

I've tried your examples but I can't get them to work.
VC++ 6 won't compile them.
Here's my original code that gets only the two error lines.

/*** SYNTAX ERROR ***/
/*** INVALID PARAMETER NAME ***/

============ code start =============== ======
ifstream infile("paramet ers.txt");

if (!infile) return (1);

bool done=false;
char str[1000];
std::string commandResponse ;

while (!done && infile.good()){
infile.getline( str,100-1);
if (strstr(str,"/***")){
commandResponse += str;
infile.seekg(1, ios::cur);
infile.getline( str,100-1);
commandResponse += str;
commandResponse += "\n";
}
}

infile.close();

============ code ends =============== ======

Could you be so kind to help me out getting your code
inserted so that it would work.
I've included almost everything I can think of that would
help, but no use.

#include <iostream.h>
#include <fstream.h>
#include <string>
#include <vector>

I've tried including iostream & fstream without the .h too but
it didn't help. The compiler just won't compile. It either says
that there's too few parameters or cannot convert paramater 1
or 2 to something...

I've tried to dabble with this for a while now and I really need
to get it working. It would be nice if I could just fiddle with
this code as long as it takes for me to get it working, but I'm
in a bit of a hurry so I'll take any help I can get.

Thanks.

----
mkarja

[David Rubin]

"Chris \( Val \)" <ch******@bigpo nd.com.au> wrote in message news:<2t******* ******@uni-berlin.de>...

"David Rubin" <da********@war pmail.net> wrote in message
news:82******** *************** *@posting.googl e.com...
| "Chris \( Val \)" <ch******@bigpo nd.com.au> wrote in message
news:<2t******* ******@uni-berlin.de>...
| > "mkarja" <mm**********@h otmail.com> wrote in message
| > news:75******** *************** ***@posting.goo gle.com...

| > | I have a log file in txt format. I need to read the file if
| > | there's any errors. There's two lines that has error information
| > | if something goes wrong. I need to get the errors and the command
| > | that caused the error which is about three rows above the first
| > | error line. I have to use the error as a search string because
| > | the command changes everytime so I can't use the command as a
| > | search string.
[snip] | The typical solution is to read lines into a circular buffer with the
| minimum capacity necessary. This seems to be 5 in your case: 2 lines
| of interest, plus the 3 previous lines.

Yes, of course :-)

I thought it was pretty clear from the above
that one would therefore write something like:

std::ifstream:: pos_type Previous( OneLine * 3 );
InFile.seekg( -Previous, std::ios_base:: cur );
The problem is here [pasted from your previous post]
| > // Approx line size in the file...
| > std::ifstream:: pos_type OneLine( 100 );

This is a rather brittle solution.

/david

[Chris \( Val \)]

"mkarja" <mm**********@h otmail.com> wrote in message
news:75******** *************** ***@posting.goo gle.com...
|> Yes, of course :-)
| >
| > I thought it was pretty clear from the above
| > that one would therefore write something like:
| >
| > std::ifstream:: pos_type Previous( OneLine * 3 );
| > InFile.seekg( -Previous, std::ios_base:: cur );
| >
| > // Read '5' lines into an buffer, or deal with
| > // each one individually...
| >
| > Cheers.
| > Chris Val
|
| I've tried your examples but I can't get them to work.
| VC++ 6 won't compile them.
| Here's my original code that gets only the two error lines.
|
| /*** SYNTAX ERROR ***/
| /*** INVALID PARAMETER NAME ***/

[snip]

I don't have VC++ installed at the moment, but even then,
without the appropriate error messages, we would only be
guessing at the problem.

Please post the exact messages emitted by the compiler.

Fwiw, did you use an appropriate namespace qualification ?

Cheers.
Chris Val

[mkarja]

> [snip]

Ok, try this:

Given the following data file:

XXXXXXXXXXXXXXX XXXXXXXXXXXXXXX XXXX
XXXXXXXXXXXXXXX XXXXXXXXXXXXXXX XXXX
XXXXXXXXXXXXX BEFORE XXXXXXXXXXXXX
XXXXXXXXXXXXXXX XXXXXXXXXXXXXXX XXXX
XXXXXXXXXXX TEST LINE XXXXXXXXXXXX
XXXXXXXXXXXXXXX XXXXXXXXXXXXXXX XXXX
XXXXXXXXXXXXX AFTER XXXXXXXXXXXXXX
XXXXXXXXXXXXXXX XXXXXXXXXXXXXXX XXXX
XXXXXXXXXXXXXXX XXXXXXXXXXXXXXX XXXX
XXXXXXXXXXXXXXX XXXXXXXXXXXXXXX XXXX

# include <iostream>
# include <fstream>
# include <ostream>
# include <string>
# include <cstddef>

int main()
{
std::ifstream InFile( "100000.txt ", std::ios_base:: binary );

std::string Buffer;
std::ifstream:: pos_type OneLine( 36 );

while( std::getline( InFile, Buffer ) )
{
if( Buffer.find( "TEST LINE" ) != std::string::np os )
break;
}

InFile.seekg( -OneLine*3, std::ios_base:: cur );

std::size_t NrLines( 6 );
while( std::getline( InFile, Buffer ) && --NrLines > 0 )
std::cout << Buffer << std::endl;

return 0;
}

-- PRODUCES THE FOLOWING OUTPUT --

XXXXXXXXXXXXX BEFORE XXXXXXXXXXXXX
XXXXXXXXXXXXXXX XXXXXXXXXXXXXXX XXXX
XXXXXXXXXXX TEST LINE XXXXXXXXXXXX
XXXXXXXXXXXXXXX XXXXXXXXXXXXXXX XXXX
XXXXXXXXXXXXX AFTER XXXXXXXXXXXXXX

HTH.
Chris Val

Thanks a million. This works just as I needed.
Three hip, hip, hurraahs to you :)

----
mkarja

[mkarja]

>

Thanks a million. This works just as I needed.
Three hip, hip, hurraahs to you :)

----
mkarja

Or at least I thought it worked as I needed.
I was under the impression that the log file would be pretty
much the same allways. It turned out it isn't. I had looked at
several log files and they all were the same, except the command
and error messages, so I thought they all were basically the
same. The command that produces the error may be, like I said
earlier, three lines above the first error message or it may be
four rows above it. It might even be five or two or whatever
rows above it, I don't know.
So the example given by Chris won't work correctly if the row is
more than three rows above the error message. I've modified it so
that I can get the command even if it's four rows above the error
but this way if the command is perhaps two rows above the error
then there will be some unnecessary rows in the result if I go
up four rows.
Is it possible to do the example that Chris gave so that when
the /*** is found it would search backwards looking for some
character instead of going backwards some defined number of rows.
In this case the character would be < character, because the row
that the command is starts with the < character.

Thanks for your help so far and if you can help me with this I
think I'll be allright for a while, until I run into another
wall and need some help :)

----
mkarja