Problem With Public Variable

Question

4.00/5 (1 vote)

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Hi,
I have one dll that used by one platform(Metatrader) and another exe file.
I define one Public variable(PP) in header code and set value in
MT4_EXPFUNC double __stdcall Reza(double ppp) function.

When try call this dll from my exe it returns only Zero(0) value but if call from other platform(Metatrader) returns correct value.

C++

#define WIN32_LEAN_AND_MEAN  // Exclude rarely-used stuff from Windows headers
#include <windows.h>
#include <stdlib.h>
#include <stdio.h>

double price();
double pp;

#define MT4_EXPFUNC __declspec(dllexport)

BOOL WINAPI DllEntryPoint(HINSTANCE hDll,DWORD dwReason, LPVOID Reserved)
{
	switch(dwReason)
	{
	case DLL_PROCESS_ATTACH:
		break;
	case DLL_PROCESS_DETACH:
		break;
	}
	return TRUE;
}
  




MT4_EXPFUNC double __stdcall Reza(double ppp)
  {
   pp=ppp;
  
   return (pp);
  }


double price(){
double dd;
dd=pp;
return dd;
}

How I must define public variable to return correct value?
Regards,

Posted 9-Oct-12 5:59am

Rezame

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Comments

[no name] 9-Oct-12 12:02pm

Probably has nothing to do with your declaration. Are the calling conventions the same when calling your function from the other applications?

Rezame 9-Oct-12 12:04pm

Yes, same.
Try call that double type too.

pasztorpisti 9-Oct-12 13:19pm

What do you see in the debugger? Try to put some printffing (or outputdebugstring, or logging or whatever) as well into your code.

Rezame 9-Oct-12 14:20pm

I used MessageBox:
function: MT4_EXPFUNC double __stdcall Reza(double ppp) shows correct value
function: double price() shows incorrect, zero(0) value

pasztorpisti 9-Oct-12 14:54pm

Use a debugger instead.

nv3 9-Oct-12 17:00pm

If Reza() returns the correct value that proves that your global pp is being set correctly.

If price() is not returning the same value you might be calling a totally different function, not the one in your dll. You did not export price the you did export Reza. A debugger run will show you immediately what's going on.

Vardhraz 12-Oct-12 2:04am

within that Reza() only you can able to return the variable pp..if you want to use double price() you have to call that price() fucntion within that Reza()fucntion...

2 solutions

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chaau · Answer 1 · 2012-10-09T11:19:00

Solution 1

I think you should use the same calling convention for your price() function, i.e. declare it like:

C++

MT4_EXPFUNC double __stdcall price()

Posted 9-Oct-12 11:19am

chaau

Comments

Rezame 9-Oct-12 17:21pm

I tried same calling methods too.
When call both functions from same platform(Metatrader) works correct, but call each function from different platform returns incorrect.

chaau 9-Oct-12 17:44pm

Where do you initialise your global variable pp? What exact line of code you use?

Mohibur Rashid 9-Oct-12 20:12pm

he is doing at initialization in reza function.

chaau 9-Oct-12 20:37pm

Yes, but is he calling reza() function before price() within the same process? He might expect that calling the function within the exe will bring the value to "other platform(Metatrader)" (whatever it means)

eugene.shikhov · Answer 2 · 2012-10-09T21:58:00

Solution 2

Doing so, you have got two different instances of pp. One of them is in DLL and another in EXE. You should use dllexport for DLL header and dllimport for EXE header. Something like this:

C++

...
#ifdef M_DLL
__declspec(dllexport) double pp;
#else
__declspec(dllimport) double pp;
#endif
...

http://msdn.microsoft.com/en-us/library/9h658af8.aspx[^]

Posted 9-Oct-12 21:58pm

eugene.shikhov

Updated 9-Oct-12 22:18pm

v2

Comments

Rezame 10-Oct-12 13:15pm

When add above lines get this errors:

Creating library C:\Users\Reza\Desktop\Test_Projects\C#\Reza2\Debug\Reza2.lib and object C:\Users\Reza\Desktop\Test_Projects\C#\Reza2\Debug\Reza2.exp
1>dllmain.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) double pp" (__imp_?pp@@3NA)
1>C:\Users\Reza\Desktop\Test_Projects\C#\Reza2\Debug\Reza2.dll : fatal error LNK1120: 1 unresolved externals

eugene.shikhov 11-Oct-12 7:40am

Try _DLL instead of M_DLL.