I started to write an EA for the Empty4 platform and got stuck using class members in MQL4.
I come from C# background where that thing is really easy to do. Hope someone will help me doing that in MQL4.
So suppose I have a small class called #PivotPoint that has members called #Index & #PP.
Then I would like to create an array from 6 instances of the #PivotPoint class and in the body of the EA I need to add and update those instances. After that {for testing purposes} I need to create dot objects on a chart from those pivot points.
Here is a sample of my code:
Code: Select all
bool doDots = true;
string obj_name = "dot";
long current_chart_id;
class PivotPoint
{
public:
int Index;
double PP;
// Default constructor
PivotPoint(void){};
// Parametric constructor
PivotPoint(int index, double pp)
{
Index = index;
PP = pp;
};
};
// create chain of 6 pivot points for the fork chain
PivotPoint *fork_chain[6];
// counter for the elements added in *fork_chain
int fork_counter = 0;
void OnStart()
{
int index_ = iBars(_Symbol, _Period);
double high_ = iHigh(_Symbol, _Period, 1);
// increment #fork_counter
fork_counter++;
// add the result to #fork_chain
add_new_pivot(fork_chain, index_, high_, fork_counter);
// create new fork PivotPoint
PivotPoint *new_pp = new PivotPoint(index_, high_);
if(doDots == true)
{
draw_dot(obj_name + IntegerToString(new_pp.Index),
new_pp.Index, new_pp.PP);
}
}
void add_new_pivot(PivotPoint* &arr_pp[], int index_, double high_,
int counter)
{
///<summary>Adds new #PivotPoint instance to a #PivotPoint
/// _ list.</summary>
// find array size
int len = ArraySize(arr_pp);
PivotPoint pp_ = new PivotPoint(index_, high_);
if(counter <= len)
{
//// ------- Compilable in MetaEditor (MQL4, 5.00 build 2375)
//// ------- Error "invalid pointer access" on row 65 in Empty4
//arr_pp[counter - 1] = pp_;
arr_pp[counter - 1].Index = pp_.Index; // row 65
arr_pp[counter - 1].PP = pp_.PP;
}
else
{
ArrayResize(arr_pp, len + 1);
//arr_pp[len] = pp_;
arr_pp[len].Index = pp_.Index;
arr_pp[len].PP = pp_.PP;
EraseOrdered(arr_pp, 0);
}
}
template <typename T> void EraseOrdered(T& A[], int iPos)
{
///<summary>Deletes certain index number from an array.</summary>
int iLast;
for(
iLast = ArraySize(A) - 1;
iPos < iLast;
++iPos
)
{
A[iPos] = A[iPos + 1];
}
ArrayResize(A, iLast);
}
void draw_dot(string objName, int dt_index, double price)
{
///<summary>Draw dot object on the chart.</summary>
ObjectCreate
(
objName + (string)Time[dt_index], // object name
OBJ_TEXT, // object type
0, // window index
Time[dt_index], // time of the first anchor point
price // price of the first anchor point
);
ObjectSetText
(
objName + (string)Time[dt_index],
CharToStr(159),
14, // size of the font
"Wingdings", // name of the font
Red // color of the dot
);
}
Obviously I can't access the members of the PivotPoint class in the array the way I am trying to. Hope you can give me a hand on that.
Technically in the code above I can add new instance of the PivotPoint class and later draw the dot by only using #index_ and #high_. The problem is that later in my code {not included here} I need to update a previous instance of that class in the array so I still need to be able to access the members of that previous instance.
EDIT:
I have missed to include a line in #OnStart about #current_chart_id variable:
Code: Select all
if(doDots == true)
current_chart_id = ChartID()
