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question about variable initialization

  • #1
  • First Post: Feb 1, 2011 11:10pm Feb 1, 2011 11:10pm
greetings everyone. i have a small question:

what happens to the initialized variables inside function and main function, when the EA is running?

for example:

void start()
{

bool NewDay=false;

... if timecurrent==23:59
NewDay=True

NewDay = checkforTrade() //if an order is executed, "false" assigned to NewDay

...

return;
}


is flag set to false at every tick when the EA is running? or just once when the EA starts for the first time.

==================

what i am trying to do is trade one order per day. so i need a variable to flag a new day and then set to false throughout the day.

please, let me know if there is another trick to have only one trade per day.

thanks
  • #2
  • Feb 2, 2011 12:09am Feb 2, 2011 12:09am
By declaring a variable as static in the same section of code as the externals, it will retain the same value every time the EA is invoked by a new tick until it is assigned a new value. It is only initialized once at EA loading.

A local variable in the start() function is initialized for every tick.

The following code should do what you want. barStart and todayStart need to be declared as static datetime variables.


Inserted Code
   if (barStart < Time[0]) // start of new bar
   {
      barStart = Time[0];
      
      if (todayStart < StrToTime(TimeToStr(TimeCurrent(), TIME_DATE)))  // start of new day
      {
         todayStart = StrToTime(TimeToStr(TimeCurrent(), TIME_DATE));
         // other logic 
      } 

   }
  • #3
  • Feb 2, 2011 6:12am Feb 2, 2011 6:12am
Quoting rocket4x
what i am trying to do is trade one order per day. so i need a variable to flag a new day and then set to false throughout the day.

please, let me know if there is another trick to have only one trade per day.

thanks

hey rocket...... additionally be sure to consider any unplanned events.....

if you count the orders placed today and use the count as a condition, or flag as you say, that might avoid any variable re-initalization problems.........

rough example below.....h



Inserted Code
 
int Count()
   {
   int total;
 
   for(int i = OrdersTotal()-1; i >=0; i--)
   {
 
   OrderSelect(i, SELECT_BY_POS,MODE_TRADES);
 
   if(TimeDay(OrderOpenTime()) != Day()) continue;
 
   total++;
to trade and code, keep both simple... no call to impress....h
  • #4
  • Feb 2, 2011 6:14am Feb 2, 2011 6:14am
Quoting CodeMeister
By declaring a variable as static in the same section of code as the externals, it will retain the same value every time the EA is invoked by a new tick until it is assigned a new value. It is only initialized once at EA loading.

A local variable in the start() function is initialized for every tick.

The following code should do what you want. barStart and todayStart need to be declared as static datetime variables.


CodeMeister

This is a little misleading. I am not posting this directed to you personaly but to all, as I have seen this same misuse of the static tag meny times.


by declaring a veriable as global scope (in the same section of code as the externals) your variables are not re-initialized on each tick, they are only initialized at start up, they automaticly keep their last assigned value until changed. the static tag is not needed in that area of the code and has no effect on global scope variables. (to make this even more confusing. MT, depending on the programs exit code, doesnot always re-initialize these globals at startup. Like when you open the dialog box of your indicator, ea, or script that program is stoped and restarted but the globals are not re-initialized.)

If on the other hand you decleare a variable as local, within any function procedure, then you can use the static tag there to force the veriable to retain its last given value on each call of the function. It is only initialize once on the first call to the function and will not get re-initialized (on each tick). In which case if you have a variable declared as ' static bool VariableName; ' that variable will keep its value, last assigned, on each call of the function.

The only difference between useing globally decleared variables, instead of static locally dedcleared variables (within your function) is that a locally decleared variable can not be seen or changed outside of its function and globals can be seen and changed any were, through out the code. so if you have no need to change the value of this variable outside the function it is best to decleare it as a static local scope variable inside the function itself.



Inserted Code
 
void start()
{
 
[color=red]static[/color] bool NewDay=false;
 
... if timecurrent==23:59
NewDay=True
 
...
 
return;
}




And for those that I haven't totally comfused, theres another type of declaration not mentioned in MT documents and thats the modually decleared variables that are decleared within the global area of code modules (such as libaraies). These are seen though out your code modual but not out side of it. This means if you create a libaray and you what a variable to be seen by all the function within the libaray it can be decleared in the global area of the libaray this will make it accessable to every function in the libaray but not outside of it.

If we have a trade management libaray and one function in the libaray calculates the StopLoss and assigns it to a modual scope variable its value can be seen by all the other trade function and will not have to be recalculed inside of each function. The value however can not be seen outside the libaray itself.

Keit
Trader Keit ... Methods Of A Dirt Road Mad Man....
  • #5
  • Feb 2, 2011 1:10pm Feb 2, 2011 1:10pm
great. thanks.


Quoting CodeMeister
By declaring a variable as static in the same section of code as the externals, it will retain the same value every time the EA is invoked by a new tick until it is assigned a new value. It is only initialized once at EA loading.

A local variable in the start() function is initialized for every tick.

The following code should do what you want. barStart and todayStart need to be declared as static datetime variables.


[code]...
  • #6
  • Feb 2, 2011 1:14pm Feb 2, 2011 1:14pm
thanks for clarification.


Quoting CockeyedCowboy
CodeMeister

This is a little misleading. I am not posting this directed to you personaly but to all, as I have seen this same misuse of the static tag meny times.


by declaring a veriable as global scope (in the same section of code as the externals) your variables are not re-initialized on each tick, they are only initialized at start up, they automaticly keep their last assigned value until changed. the static tag is not needed in that area of the code and has no effect on global scope variables. (to make this even more confusing. MT,...
  • #7
  • Last Post: Feb 2, 2011 9:38pm Feb 2, 2011 9:38pm
Quoting hayseed
hey rocket...... additionally be sure to consider any unplanned events.....

if you count the orders placed today and use the count as a condition, or flag as you say, that might avoid any variable re-initalization problems.........

rough example below.....h



Inserted Code
 
int Count()
   {
   int total;
 
   for(int i = OrdersTotal()-1; i >=0; i--)
   {
 
   OrderSelect(i, SELECT_BY_POS,MODE_TRADES);
 
   if(TimeDay(OrderOpenTime()) != Day()) continue;
 
   total++;
thanks. more safety.
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