Reading a file in FreePascal

Question

I have a text file with the specified structure, namely (for each line): char, space, char, space, double value, end line. For instance,

qw 1.23 er 4.56 ty 7.89 

What is the correct way to “extract” these values ​​in Free Pascal?

Answer 1

FreePascal has an SScanF function in SysUtils (you can know if from other languages ​​..)

I modified the RRUZ example to show how to use it.

 uses SysUtils; type TData=object Val1 , Val2 : String; Val3 : Double; end; procedure ProcessFile(aFileName:String); var F : Text; LData : TData; Line : String; begin DecimalSeparator:='.'; AssignFile(F,aFileName); Reset(F); while not eof(F) do begin ReadLn(F,Line); SScanf(Line,'%s %s %f',[@LData.Val1,@LData.Val2,@LData.Val3]); //do something with the data WriteLn(LData.Val1); WriteLn(LData.Val2); WriteLn(LData.Val3); end; end; begin ProcessFile('C:\Bar\Foo\Data.txt'); Writeln('Press Enter to exit'); Readln; end. 

Answer 2

You can use the TStringList class to load a file and DelimitedText to split the values ​​into another TStringList, and then save the values ​​in a record.

Check out this sample.

 {$mode objfpc}{$H+} uses Classes, SysUtils; {$R *.res} type TData=record Val1: Char; Val2: Char; Val3: Double; end; procedure ProcessFile; var LFile : TStringList; Line : TStringList; i : Integer; LData : TData; LFormat: TFormatSettings; begin //set the propert format for the foat values LFormat:=DefaultFormatSettings; LFormat.DecimalSeparator:='.'; LFile:=TStringList.Create; Line :=TStringList.Create; try //load the file LFile.LoadFromFile('C:\Bar\Foo\Data.txt'); Line.Delimiter:=' '; for i:=0 to LFile.Count-1 do begin //read the line and split the result Line.DelimitedText:=LFile[i]; //some basic check if Line.Count <> 3 then raise Exception.Create('Wrong data length'); //you can add additional check here LData.Val1:=Line[0][3]; LData.Val2:=Line[1][4]; LData.Val3:=StrToFloat(Line[2],LFormat); //do something with the data WriteLn(LData.Val1); WriteLn(LData.Val2); WriteLn(LData.Val3); end; finally Line.Free; LFile.Free; end; end; begin try ProcessFile; except on E:Exception do Writeln(E.Classname, ':', E.Message); end; Writeln('Press Enter to exit'); Readln; end. 

Answer 3

Let's say that we are interested in reading the file provided by the command line argument after the switch containing the replacement weights for the characters.

 program WeightFileRead; uses SysUtils, StrUtils; var MyFile : TextFile; FirstChar, SecondChar, DummyChar : Char; Weight : Double; begin if GetCmdLineArg ('editweights', StdSwitchChars) = '' then begin WriteLn ('Syntax: WeightFileRead -editweights filename'); exit end; AssignFile (MyFile, GetCmdLineArg ('editweights', StdSwitchChars)); Reset (MyFile); try while not EOF (MyFile) do begin ReadLn (MyFile, FirstChar, DummyChar, SecondChar, Weight); WriteLn ('A: ', FirstChar, '; B: ', SecondChar, '; W: ', Weight:0:1); end finally CloseFile (MyFile) end end. 

In a more general setting, when the first two entries may be longer lines, we can use ExtractWord , which finds the n th word separated by spaces in the line (or ExtractSubstr , which processes several spaces together as entering an empty word), and convert the third to number.

 program WeightFileRead2; uses SysUtils, StrUtils; var MyFile : TextFile; FileLine : String; begin if GetCmdLineArg ('editweights', StdSwitchChars) = '' then begin WriteLn ('Syntax: WeightFileRead -editweights filename'); exit end; AssignFile (MyFile, GetCmdLineArg ('editweights', StdSwitchChars)); Reset (MyFile); try while not EOF (MyFile) do begin ReadLn (MyFile, FileLine); WriteLn ('A: ', ExtractWord (1, FileLine, [' ']), '; B: ', ExtractWord (2, FileLine, [' ']), '; W: ', StrToFloat (ExtractWord (3, FileLine, [' '])):0:1); end finally CloseFile (MyFile) end end. 

Note. I use [' '] and not StdWordDelims since I don't want to. or to be a word separator.