Re: [fpc-pascal] read lines at end of file
On 04/11/2011 12:32 PM, John Lee wrote: Need to read the last 4 lines (txt) of a very large log file 100M bytes, 100k lines or more lots of times - of course I can read through the file in the normal way but this is rather slow. Is there a way to 'read lines from the end'? I note that unix tail or its port to windows does this very fast so guess there must be a fast way to do it in pascal too? TIA for any ideas John ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal Hmm, could first have the reader enumerate the number of lines in the file, then read through the files using the "total number of lines - 4" variable and then start displaying the lines after that variable has been reached. If necessary, I would be happy to see what I can come up with here and then post it to the mailing list. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: Re[2]: [fpc-pascal] read lines at end of file
So the idea is to open file eg as file of array [1:65536] of char or something similar, seek & read to end of file, then go through the last array converting to strings by finding crlfs correct? Is this the simplest way? If not any outline code? John On , José Mejuto wrote: Hello FPC-Pascal, Monday, April 11, 2011, 7:55:01 PM, you wrote: >> The idea is easy, instead reading forward, you read backwards in >> blocks of, say, 64 Kb and count lines back. If not enougth lines you >> insert another 64 Kb before and so on. Average line is usually less >> than 100 bytes, so each 64 Kb are usually more than 600 lines. Read of >> 64 Kb usually takes the same time as read any lower amount when the >> block is 4096 bytes aligned. MG> You can not really read backwards. You can use MG> something like TFileStream.Seek(-4096,soEnd). I think that the "read backwards in blocks" already stated that fact, but nice annotation. -- Best regards, José ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] generic, specialize keywords in mode delphi in FPC trunk
2011/4/12 Paul Ishenin :
> 12.04.2011 4:22, cobines wrote:
>>
>> Hello.
>>
>> Following program:
>>
>> program a;
>> {$mode delphi}
>> type
>> generic TGen = class end;
>> TSpc = specialize TGen;
>> begin
>> end.
>>
>> compiles with FPC 2.4.2, but not with 2.5.1 rev. 17306:
>>
>> a.pas(4,11) Fatal: Syntax error, "=" expected but "identifier TGEN" found
>> a.pas(5,21) Error: Identifier not found "specialize"
>> a.pas(5,21) Error: Error in type definition
>> a.pas(5,21) Fatal: Syntax error, ";" expected but "identifier TGEN" found
>>
>> "generic" and "specialize" are not allowed in delphi mode in 2.5.1 but
>> they are required in 2.4.2.
>>
>> Is this a conscious change? There is no mention of this on Wiki User
>> Changes 2.4.4 or User Changes Trunk pages.
>
> In mode delphi FPC understands delphi generic syntax. I did not write a line
> to the
>
> User Changes Trunk because this work is not finished. But looking at my free
> time I don't think it will be finished by me, so I will add a note there
> today.
OK.
Thanks.
--
cobines
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[fpc-pascal] Re: generic, specialize keywords in mode delphi in FPC trunk
Since FPC in Delphi mode supports Delphi style generics syntax, FPC's own generics syntax was removed from this mode. You can still use it from ObjFPC mode. -- View this message in context: http://free-pascal-general.1045716.n5.nabble.com/generic-specialize-keywords-in-mode-delphi-in-FPC-trunk-tp4296801p4296946.html Sent from the Free Pascal - General mailing list archive at Nabble.com. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] generic, specialize keywords in mode delphi in FPC trunk
12.04.2011 4:22, cobines wrote:
Hello.
Following program:
program a;
{$mode delphi}
type
generic TGen = class end;
TSpc = specialize TGen;
begin
end.
compiles with FPC 2.4.2, but not with 2.5.1 rev. 17306:
a.pas(4,11) Fatal: Syntax error, "=" expected but "identifier TGEN" found
a.pas(5,21) Error: Identifier not found "specialize"
a.pas(5,21) Error: Error in type definition
a.pas(5,21) Fatal: Syntax error, ";" expected but "identifier TGEN" found
"generic" and "specialize" are not allowed in delphi mode in 2.5.1 but
they are required in 2.4.2.
Is this a conscious change? There is no mention of this on Wiki User
Changes 2.4.4 or User Changes Trunk pages.
In mode delphi FPC understands delphi generic syntax. I did not write a
line to the
User Changes Trunk because this work is not finished. But looking at my free
time I don't think it will be finished by me, so I will add a note there today.
Best regards,
Paul Ishenin
___
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[fpc-pascal] generic, specialize keywords in mode delphi in FPC trunk
Hello.
Following program:
program a;
{$mode delphi}
type
generic TGen = class end;
TSpc = specialize TGen;
begin
end.
compiles with FPC 2.4.2, but not with 2.5.1 rev. 17306:
a.pas(4,11) Fatal: Syntax error, "=" expected but "identifier TGEN" found
a.pas(5,21) Error: Identifier not found "specialize"
a.pas(5,21) Error: Error in type definition
a.pas(5,21) Fatal: Syntax error, ";" expected but "identifier TGEN" found
"generic" and "specialize" are not allowed in delphi mode in 2.5.1 but
they are required in 2.4.2.
Is this a conscious change? There is no mention of this on Wiki User
Changes 2.4.4 or User Changes Trunk pages.
--
cobines
___
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Re[2]: [fpc-pascal] read lines at end of file
Hello FPC-Pascal, Monday, April 11, 2011, 7:55:01 PM, you wrote: >> The idea is easy, instead reading forward, you read backwards in >> blocks of, say, 64 Kb and count lines back. If not enougth lines you >> insert another 64 Kb before and so on. Average line is usually less >> than 100 bytes, so each 64 Kb are usually more than 600 lines. Read of >> 64 Kb usually takes the same time as read any lower amount when the >> block is 4096 bytes aligned. MG> You can not really read backwards. You can use MG> something like TFileStream.Seek(-4096,soEnd). I think that the "read backwards in blocks" already stated that fact, but nice annotation. -- Best regards, José ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] read lines at end of file
On Mon, 11 Apr 2011 19:45:10 +0200 José Mejuto wrote: > Hello FPC-Pascal, > > Monday, April 11, 2011, 6:32:20 PM, you wrote: > > JL> Need to read the last 4 lines (txt) of a very large log file 100M bytes, > JL> 100k lines or more lots of times - of course I can read through the file > in > JL> the normal way but this is rather slow. Is there a way to 'read lines from > JL> the end'? I note that unix tail or its port to windows does this very fast > JL> so guess there must be a fast way to do it in pascal too? > > The idea is easy, instead reading forward, you read backwards in > blocks of, say, 64 Kb and count lines back. If not enougth lines you > insert another 64 Kb before and so on. Average line is usually less > than 100 bytes, so each 64 Kb are usually more than 600 lines. Read of > 64 Kb usually takes the same time as read any lower amount when the > block is 4096 bytes aligned. You can not really read backwards. You can use something like TFileStream.Seek(-4096,soEnd). Mattias ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] read lines at end of file
Hello FPC-Pascal, Monday, April 11, 2011, 6:32:20 PM, you wrote: JL> Need to read the last 4 lines (txt) of a very large log file 100M bytes, JL> 100k lines or more lots of times - of course I can read through the file in JL> the normal way but this is rather slow. Is there a way to 'read lines from JL> the end'? I note that unix tail or its port to windows does this very fast JL> so guess there must be a fast way to do it in pascal too? The idea is easy, instead reading forward, you read backwards in blocks of, say, 64 Kb and count lines back. If not enougth lines you insert another 64 Kb before and so on. Average line is usually less than 100 bytes, so each 64 Kb are usually more than 600 lines. Read of 64 Kb usually takes the same time as read any lower amount when the block is 4096 bytes aligned. -- Best regards, José ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
[fpc-pascal] read lines at end of file
Need to read the last 4 lines (txt) of a very large log file 100M bytes, 100k lines or more lots of times - of course I can read through the file in the normal way but this is rather slow. Is there a way to 'read lines from the end'? I note that unix tail or its port to windows does this very fast so guess there must be a fast way to do it in pascal too? TIA for any ideas John ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
