Please, Why Can not return var by parameter from functions in DLL ???

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Can not return var by parameter from functions in DLL ???

there are a function in DLL,

======================

MT4_EXPFUNC char*__stdcall GetState(int& st,char* which,int& prd)
{
//st = 1;
which = "EURUSD";
// prd = 5;

return (which);
}

====================

if I call such function in a script: MT version 224

string which = "000", ss="";

int a=0,b=0;

ss = GetState(a, which,b);

Print (ss," ", which);

get ss "EURUSD", which still is "000" !!!!!!!!!!!!!!!!

--------------------------------------------------

if I change GetState function to

======================

MT4_EXPFUNC char*__stdcall GetState(int& st,char* which,int& prd)
{
st = 1;
which = "EURUSD";
prd = 5;

return (which);
}

====================

MY GOD! MT deaded!!!!!!!!!!! and now, MT do not allow debug DLL when MT runing ! so I can not debug what happon in DLL!! in so simple code!!!!

--------------------------------------------------

Who know why ?

 

Hi

Check your use of pointers. You declare "which" as string and the function requires a pointer to a string. If you get a pointer wrong the compiler can't tell you and the results are usually catastrophic.

 

Thanks,

now I debug this DLL with a console win32 app, char* which is error using, but not induced MTdead.

but why int& st and int& prd made MT dead ?

with console win32 app, can sure that int& st and int& prd can be assign value and return OK inside DLL.

 
DxdCn:

Thanks,

now I debug this DLL with a console win32 app, char* which is error using, but not induced MTdead.

but why int& st and int& prd made MT dead ?

with console win32 app, can sure that int& st and int& prd can be assign value and return OK inside DLL.

Sorry I did not read the whole thing very carefully but in my experience MT4 does not like it when you try to resize its variables in a dll ...

I had similar issues trying to fill out an array, the array had to define and of the right size before my dll could successfully fill it up.


So for a test try setting in MT4 you string which variable to which = "0000000";

Then have it call your dll function and it will most likely work this time ...


Patrick

 

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?

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