Discussion of article "Getting Rid of Self-Made DLLs"

[MetaQuotes]

New article Getting Rid of Self-Made DLLs is published:

If MQL5 language functional is not enough for fulfilling tasks, an MQL5 programmer has to use additional tools. He\she has to pass to another programming language and create an intermediate DLL. MQL5 has the possibility to present various data types and transfer them to API but, unfortunately, MQL5 cannot solve the issue concerning data extraction from the accepted pointer. In this article we will dot all the "i"s and show simple mechanisms of exchanging and working with complex data types.

Author: Alex Sergeev

[krisn]

Most useful and informative article regarding working with external DLL APIs. Thank you so much.

[lippmaje]

Example 4. Copying the structures by means of MQL5
struct str1
{
  double d; // 8 bytes
  long l;   // 8 bytes
  int i[3]; // 3*4=12 bytes
};
struct str2
{
  uchar c[8+8+12]; // str1 structure size
};
//+------------------------------------------------------------------+
//| Script program start function                                    |
//+------------------------------------------------------------------+
void OnStart()
{
  str1 src; 
  src.d=-1;
  src.l=20;
  //--- filling the structure parameters
  ArrayInitialize(src.i, 0); 
  str2 dst;
  //--- turning the structure into the byte array
  dst=src; 
}

Assigning structs of different types doesn't work anymore (parameter conversion not allowed - variable of the same type expected).

But it would be possible to work with unions:

struct str1
{
  double d; // 8 bytes
  long l;   // 8 bytes
  int i[3]; // 3*4=12 bytes
};
struct str2
{
  uchar c[8+8+12]; // str1 structure size
};
union union1
{
  str1 src;
  str2 dst;
};

//+------------------------------------------------------------------+
//| Script program start function                                    |
//+------------------------------------------------------------------+
void OnStart()
{
  union1 u; 
  u.src.d=-1;
  u.src.l=20;
  //--- filling the structure parameters
  ArrayInitialize(u.src.i, 0); 

  //--- the byte array representing the structure is in dst.c
  ArrayPrint(u.dst.c);