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46 lines
2.1 KiB
ObjectPascal
46 lines
2.1 KiB
ObjectPascal
program Test;
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{ Show how to seek to an OFFSET (not a line number) in a textfile, }
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{ without using asm. Arne de Bruijn, 1994, PD }
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uses Dos; { For TextRec and FileRec }
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var
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F:text;
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L:longint;
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S:string;
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begin
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assign(F,'TEST.PAS'); { Assign F to itself }
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reset(F); { Open it (as a textfile) }
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ReadLn(F); { Just read some lines }
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ReadLn(F);
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ReadLn(F);
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FileRec((@F)^).Mode:=fmInOut; { Set to binary mode }
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{ (The (@F)^ part is to let TP 'forget' the type of the structure, so }
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{ you can type-caste it to everything (note that with and without (@X)^ }
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{ can give a different value, longint(bytevar) gives the same value as }
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{ bytevar, while longint((@bytevar)^) gives the same as }
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{ longint absolute Bytevar (i.e. all 4 bytes in a longint are readed }
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{ from memory instead of 3 filled with zeros))) }
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FileRec((@F)^).RecSize:=1; { Set record size to 1 (a byte)}
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L:=(FilePos(File((@F)^))-TextRec(F).BufEnd)+TextRec(F).BufPos;
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{... This line didn't work the last time I tried, it chokes on the "File"
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typecasting thing.}
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{ Get the fileposition, subtract the already readed buffer, and add the }
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{ position in that buffer }
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TextRec(F).Mode:=fmInput; { Set back to text mode }
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TextRec(F).BufSize:=SizeOf(TextBuf); { BufSize overwritten by RecSize }
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{ Doesn't work with SetTextBuf! }
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ReadLn(F,S); { Read the next line }
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WriteLn('Next line:',S); { Display it }
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FileRec((@F)^).Mode:=fmInOut; { Set to binary mode }
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FileRec((@F)^).RecSize:=1; { Set record size to 1 (a byte)}
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Seek(File((@F)^),L); { Do the seek }
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{... And again here.}
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TextRec(F).Mode:=fmInput; { Set back to text mode }
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TextRec(F).BufSize:=SizeOf(TextBuf); { Doesn't work with SetTextBuf! }
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TextRec(F).BufPos:=0; TextRec(F).BufEnd:=0; { Reset buffer counters }
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ReadLn(F,S); { Show that it worked, the same }
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WriteLn('That line again:',S); { line readed again! }
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Close(F); { Close it }
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end.
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