function replace_x_y(textfilename:string;row,col,length:integer;replacestring:string);
var i:integer;
f,f1:textfile;
newline,stringline:string;
begin
assignfile (f,testfilename);
assignfile (f1,"temp");
while .not. eof(f)
begin
readln(f,stringline);
if i = row
newline := format('%s%s%s',[copy (stringline,1,col+1),replacestring,copy(stringline,col+length+1,strlength(stringline)-col-length)]);
stringline := newline;
endi
writeln(f1,stringline);
end;
{change f1 to f}
end;