主题：exdata和exdataset

里面部分内容没能理解确认，求教

 input:account(888888,1,999999,1);

runmode:0;

begintime:=currenttime>=091500 and currenttime<=145500;
endtime:=currenttime>=145930;

buycond:=begintime;
sellcond:=begintime;

myaccount:=''+account;        //“+account前的双引号及加号有什么特别意义？
mycash:=taccount2(19,myaccount);
myholding:=extgbdata(myaccount+'_'+formulaname+'_'+datatype+'_'+stklabel+'_holding');     // 这句括号里的加号是字符？还是整个都是字符串？

slippage:=2*mindiff;

if myholding=0 then begin
if buycond then begin
buyprice:=close+slippage;
lots:=intpart(mycash/(buyprice*multiplier*taccount(41)));

if lots>=1 then begin
tbuy(1,lots,lmt,buyprice,0,myaccount,0);
extgbdataset(myaccount+'_'+formulaname+'_'+datatype+'_'+stklabel+'_holding',lots);
end
end
end

if myholding=0 then begin
if sellcond then begin
sellprice:=close-slippage;
lots:=intpart(mycash/(sellprice*multiplier*taccount(42)));

if lots>=1 then begin
tbuyshort(1,lots,lmt,sellprice,0,myaccount,0);
extgbdataset(myaccount+'_'+formulaname+'_'+datatype+'_'+stklabel+'_holding',-lots);
end
end
end

if myholding>0 then begin
if endtime then begin
tsell(1,myholding,lmt,close-slippage,myaccount,0);
extgbdataset(myaccount+'_'+formulaname+'_'+datatype+'_'+stklabel+'_holding',0);
end
end

if myholding<0 then begin
if endtime then begin
tsellshort(1,myholding,lmt,close+slippage,myaccount,0);
extgbdataset(myaccount+'_'+formulaname+'_'+datatype+'_'+stklabel+'_holding',0);
end
end