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DLL implementation problem

  • #1
  • First Post: Mar 9, 2011 7:00am Mar 9, 2011 7:00am
Hi,

I have a problem, if you could help me. The problem is that I’m trying to implement my DLL function in MQL script, but it doesn’t work. The example is very simple.

VS2010 C++ code
Inserted Code
[color=#0000ff]#include[/color][font=Courier New][size=2][color=#a31515][font=Courier New][size=2][color=#a31515][font=Courier New][size=2][color=#a31515]"stdafx.h"[/color][/size][/font]
[/color][/size][/font][/color][/size][/font][font=Courier New][size=2][color=#0000ff][font=Courier New][size=2][color=#0000ff][font=Courier New][size=2][color=#0000ff]__declspec[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Courier New][size=2][font=Courier New][size=2]([/size][/font][/size][/font][font=Courier New][size=2][color=#0000ff][font=Courier New][size=2][color=#0000ff][font=Courier New][size=2][color=#0000ff]dllexport[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Courier New][size=2][font=Courier New][size=2]) [/size][/font][/size][/font][font=Courier New][size=2][color=#0000ff][font=Courier New][size=2][color=#0000ff][font=Courier New][size=2][color=#0000ff]double[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Courier New][size=2][color=#0000ff][font=Courier New][size=2][color=#0000ff][font=Courier New][size=2][color=#0000ff]__stdcall[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Courier New][size=2][font=Courier New][size=2] BoxVolume([/size][/font][/size][/font][font=Courier New][size=2][color=#0000ff][font=Courier New][size=2][color=#0000ff][font=Courier New][size=2][color=#0000ff]double[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Courier New][size=2][font=Courier New][size=2] L, [/size][/font][/size][/font][font=Courier New][size=2][color=#0000ff][font=Courier New][size=2][color=#0000ff][font=Courier New][size=2][color=#0000ff]double[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Courier New][size=2][font=Courier New][size=2] H, [/size][/font][/size][/font][font=Courier New][size=2][color=#0000ff][font=Courier New][size=2][color=#0000ff][font=Courier New][size=2][color=#0000ff]double[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Courier New][size=2][font=Courier New][size=2] W)[/size][/font]
[size=2][font=Courier New]{[/font][/size]
[/size][/font][font=Courier New][size=2][color=#0000ff][font=Courier New][size=2][color=#0000ff][font=Courier New][size=2][color=#0000ff]return[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Courier New][size=2][font=Courier New][size=2] ( L * H * W );[/size][/font]
[size=2][font=Courier New]}[/font][/size]
[/size][/font]

MQL code

Inserted Code
#import "user32.dll"
   int    MessageBoxA(int hWnd, string lpText, string lpCaption, int uType);
#import "TestDLL.dll"
 double BoxVolume(double L, double H, double W);
#import
int start()
  {
  int uType,hWnd;
   MessageBoxA(hWnd, "Click OK to begin", "Click OK to begin", uType);
   Alert("Test Begin");
   Alert("Test Result: ", BoxVolume(1,2,3));
   Alert("Test End");
   return(0);
  }
The problem is that the script always stops working at the moment, when I’m calling the dll function.

Please, tell me where I’m wrong .

Thank you in advance.
  • #2
  • Mar 9, 2011 8:57am Mar 9, 2011 8:57am
I don't know if this will solve your problem, but watch your type casting:
Send doubles to a routine expecting doubles (1.0, 2.0, 3.0).
  • #3
  • Mar 9, 2011 12:16pm Mar 9, 2011 12:16pm
We have a sample DLL VS project available that adds two numbers. very simple. maybe you can compare the two and see where it's not working. hope it helps.

http://helpdesk.commercialnetworkser...loaditemid=111
BarrySDCA Commercial Network Services
  • #4
  • Mar 9, 2011 2:30pm Mar 9, 2011 2:30pm
Quoting Kenz987
I don't know if this will solve your problem, but watch your type casting:
Send doubles to a routine expecting doubles (1.0, 2.0, 3.0).
This has no impact, the import is defined with three doubles and so it will always pass three doubles to the dll, no matter where they come from. The typecast is happening on the mql4 side already, the call will always be made exactly as specified in the #import declaration.
  • #5
  • Last Post: Mar 9, 2011 2:40pm Mar 9, 2011 2:40pm
Quoting fan-tom
always stops working at the moment, when I’m calling the dll function.
"stops woking" is quite vague. What is the error code?

Most probably there is a name mangling problem. Some compilers append funny things to the exported function names to encode additional information about how to call the function.

You can either try to import the function by the name that it actually got (there are tools to find out the names of the exports) or you can explicitly instruct your compiler to use exactly the names that you give (some compilers will for example accept a .def file where you can specify such things. The user manual of your compiler will tell you the details and also there must be at least a few dozen threads in various metatrader forums about the name mangling "problem").
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