who have other opinion?

[okwh]

In DLL,

MT4_EXPFUNC char*__stdcall GetState(int& st,char* which,int& prd)

in such function, MT dead if let st= 123;

MT4_EXPFUNC char*__stdcall GetState(int* st,char* which,int* prd)

in such function, MT no dead.

Both do not change parameters st, which, prd.

only can return soththing with return(.....);

only use array to return multi variables.

This is conclusion !!!

who have other opinion?

[JC]

DxdCn wrote >>

[...] only use array to return multi variables.

This is conclusion !!!

who have other opinion?

AFAIK you're correct that MT4 crashes/doesn't work if you try passing it a non-array variable by reference, and then set the value of that variable in a DLL using a pointer. You have to use arrays instead.

For example, with the following DLL...

extern "C" int WINAPI TestDll(int * p)

{

*p *= 2;

return *p;

}

... the following MQL script causes a fatal crash (in build 220):

#import "TestDll.dll"

int TestDll(int & Param);

#import

int start()

{

int TestVar = 2;

int Result = TestDll(TestVar);

MessageBox("Result: " + Result + "\r\nValue of TestVar: " + TestVar);

}

However, the same DLL works fine if you declare the MQL stuff as follows, turning TestVar into a 1-item array rather than a plain integer:

#import "TestDll.dll"

int TestDll(int & Param[]); // The parameter is now an array - see below

#import

int start()

{

int TestVar[1] = {2}; // Declare TestVar as an array with 1 slot, and put the value 2 into it

int Result = TestDll(TestVar);

MessageBox("Result: " + Result + "\r\nValue of TestVar: " + TestVar[0]);

}