CSV - comma separated files

disclaimer

the source code of this page may not appear correctly in certain browsers
due to special characters. Have a look at the source of this HTML page
with notepad instead

Comma separated files are useful to store data tables with integer & float
in readable textfiles. It is line oriented and one one data set is a line.
A table such as :

item1	1	001232	1.2345
item2	2	234561	2.453
item3	3	123456	3.1245

is stored as :

item1,1,001232,1.2345
item2,2,234561,2.453
item3,3,123456,3.1245

processing

reading and writing them is simple :

writing to a CSV

Write a line with the usual formatting.

 assignfile(f,'xxxxx.csv');
 rewrite(f);
 for j:=0 to lines-1 do begin
   writeln(f,.....);
 closefile(f);

Reading a CSV

It sounds simple : read a line, and take it appart.
For small files, a TMemo may do :

 MyMemo.lines.loadfromfile('xxxxx.csv');

 access the lines :
 
 mystring:=MyMemo.lines[i];

For big files (>32k on Win95/98, a few MBytes for NT) TMemo is
useless. WinNT takes several minutes to load a 200MB file, and takes
another 200MB (glad to have them) during that process.

 assignfile(f,'xxxxx.csv');
 reset(f);
 while (not eof(f)) do begin 
  readln(f,mystring);
  // process the lines

 closefile(f);

is much faster. A stream or blockread approach may be faster still.

The following 3 functions may help taking the string appart :

function nextcomma(s:string;i:integer):integer;
var j:integer;
begin
 j:=i+1;
 while (j',') do inc(j);
 if (j<=length(s))and(s[j]=',') then result:=j
 else result:=-1;
end;

function GetFirstV(s:string;var i:integer;):string; // first value in a line
begin
 i:=nextcomma(s,1);
 if (i<>-1) then result:=copy(s,1,i-1)
 else result:='';
end;

function GetNextV(s:string;var i:integer;):string; // next value in a line
var j:integer;
begin
 j:=i;
 i:=nextcomma(s,j);
 if (i<>-1) then result:=copy(s,j+1,i-j-1)
 else result:=copy(s,j+1,length(s)-j);
end;

use them as :

 firstvalue:=GetFirstV(mystring,i);
 if (firstvalue<>'') then begin
  nextvalue:=GetNextV(mystring,i);
  while (nextvalue<>'') do begin    // a for loop may do
   nextvalue:=GetNextV(mystring,i);
   ..

  end;
 end;

Feedback is welcome

sponsored links

Delphi
home

last updated: 29.dec.99

Copyright (99,2000) Ing.Büro R.Tschaggelar