Help with dll building

[cucho]

Hi,
i'm building a dll (with MFC) wich i need to call it from another language.
I declare it in this way
long __declspec(dllexport) __stdcall cfinterfase(CString h);

in the body of the function i need to concatenate 2 string 1 is the argument.

so i do this

long __declspec(dllexport) __stdcall cfinterfase(CString h)
{
CString d = "";
d = "hello " + h;
return 1;
}

i don't know why when it reach the concatenation it crashes and when i put to debug its points to the function memcpy()

Anybody knows why??

thanks.

 

[cucho]

I'm forget to mention that i'm using Visual C++ 6.0 without any sp or update.

 

[williamu]

memcpy is use for the = operator in the CString class and it's telling you that there is nothing to copy. I.E. CString h is null.

William
Software Engineer
ICQ No. 56047340

 

[williamu]

That sould read memcpy is used for ...

Also you won't see the result of the concatenation when the function completes since you are adding h to d, d will go out of scope when the function terminates.

Writing DLLs for VB can be a bit tricky due to the way data is passed.

HTH


William
Software Engineer
ICQ No. 56047340

 

[cucho]

f i do this i get
long __declspec(dllexport) __stdcall cfinterfase(CString h)
{
CString d = "HELLO: ";
AfxMessageBox(d);
AfxMessageBox(h);
return 10;
}

Its display 2 message box 1 with HELLO and the other with the value of h

but if i change the last afxmessagebox with
AfxMessageBox(d + h)
I get 2 messagebox with the word HELLO but the value of h i empty insteadof the HELLO + h

 

[williamu]

As I have already said the implication is that h is not getting passed to the function. At the top of the function enter the line
ASSERT(h != NULL) ;

in debug mode if h is null then the will give an assertion error, and point you in the direction of dodgy VB code.

You might also want to trace in to the DLL and put a watch in h to see what value if any is there.

You might also consider changing the declaration of the parameter to a const char*. Because at present it is in fact expecting a CString object that VB (AFAIK) does not have.

The same applies to d change it to a char* as well.

char d[12] = "Hello " ; //Make the buffer the size you need.
strcat(d, h) ;
AfxMessageBox(d) ;


William
Software Engineer
ICQ No. 56047340

 

[williamu]

As I have already said the implication is that h is not getting passed to the function. At the top of the function enter the line
ASSERT(h != NULL) ;

in debug mode if h is null then the will give an assertion error, and point you in the direction of dodgy VB code.

You might also want to trace in to the DLL and put a watch in h to see what value if any is there.

You might also consider changing the declaration of the parameter to a const char*. Because at present it is in fact expecting a CString object that VB (AFAIK) does not have.

The same applies to d change it to a char* as well.

const char* h = {"You to"} ; // Really from VB APP.
char d[12] = "Hello " ; //Make the buffer the size you need.
strcat(d, h) ;
AfxMessageBox(d) ;

HTH

William
Software Engineer
ICQ No. 56047340

 

[williamu]

As I have already said the implication is that h is not getting passed to the function. At the top of the function enter the line
ASSERT(h != NULL) ;

in debug mode if h is null then the will give an assertion error, and point you in the direction of dodgy VB code.

You might also want to trace in to the DLL and put a watch in h to see what value if any is there.

You might also consider changing the declaration of the parameter to a const char*. Because at present it is in fact expecting a CString object that VB (AFAIK) does not have.

The same applies to d change it to a char* as well.

const char* h = {"There!"} ; // Really from VB APP.
char d[16] = "Hello " ; //Make the buffer the size you need.
strcat(d, h) ;
AfxMessageBox(d) ;

HTH

William
Software Engineer
ICQ No. 56047340