passing variable to plugin

On 12/10/2013 at 01:04, xxxxxxxx wrote:

User Information:
Cinema 4D Version:   r14 
Platform:      
Language(s) :     C++  ;

---------
Hi, 
I have been searching and trying for a while, now, but I can't get it to work to pass a variable from main (PluginStart) to my plugin, where I would like to read the value of that variable.

can someone explain how things like this work?

cheers,
Ello

On 12/10/2013 at 03:09, xxxxxxxx wrote:

Hi, you could go with a global variable for PODs (int, float, char, ...) and use it wherever you want in your entire plugin.

Int my_global_variable = 0; // allowed
  
String my_global_string; // (* ) not allowed because internal pointer table to the constructor is not build yet
String* my_global_string = nullptr; // correct!  
Bool PluginStart()
{
    my_global_string = NewObj(String);
    if (!my_global_string)
        return false;
  
    // your code
  
    return true;
}
  
void PluginEnd()
{
    DeleteMem(my_global_string);
}

(* ) If you want to use a c4d class you can use a global pointer like String* and allocate it in PluginStart and Free it in PluginEnd.

Or you store some values in the global data container.

Cheers, Seb

On 12/10/2013 at 04:58, xxxxxxxx wrote:

i guess i dont't understand. in my main.cpp i have declared a boolean:
Bool test = false;

now i want to check this boolean inside another file (myPlugin.cpp)
BaseObject *myPlugin::GetVirtualObjects(BaseObject *op, HierarchyHelp *hh)
{
if (test) //do something
...
}

of course test is undeclared here. so my question is how can i grab the variable test inside GetVirtualObjects

On 12/10/2013 at 07:48, xxxxxxxx wrote:

You can use the extern keyword. See How do I share a variable between source files in C?

Best,
-Niklas

On 12/10/2013 at 08:56, xxxxxxxx wrote:

thank you. i tried this but still i must do something wrong.

in the main.cpp i have #include "myPlugin.h"

and in myPlugin.h i have

#ifndef _myPlugin_H_
#define _myPlugin_H_

extern int myTest;

enum
{
 ...

when i try to compile i get the following error:

1>  Main.cpp
1>  myPlugin.cpp
1>     Creating library C:\Program Files\MAXON\CINEMA 4D R14\plugins\myPlugin\obj\myPlugin\x64_Debug\myPlugin.cdl64.lib and object C:\Program Files\MAXON\CINEMA 4D R14\plugins\myPlugin\obj\myPlugin\x64_Debug\myPlugin.cdl64.exp
1>Main.obj : error LNK2001: unresolved external symbol "int myTest" ([email protected]@3HA)
1>myPlugin.obj : error LNK2001: unresolved external symbol "int myTest" ([email protected]@3HA)
1>C:\Program Files\MAXON\CINEMA 4D R14\plugins\myPlugin\myPlugin.cdl64 : fatal error LNK1120: 1 unresolved externals

i found this thread http://stackoverflow.com/questions/7004031/c-unresolved-externals but i dont understand what i need to do now...

On 12/10/2013 at 09:08, xxxxxxxx wrote:

Howdy,

Well, in everything I've read about c++ programming, there seems to be a consensus that global variables are frowned upon.

What I'd suggest is to create a static variable in your main.cpp file, and create accessor functions like this:

#include "MyPlugin.h"
  
static bool test;
  
bool PluginStart(void)
{
     SetTest(false);
     // rest of startup functions....
}
  
void SetTest(bool t)
{
     test = t;
}
  
bool GetTest(void)
{
     return test;
}

Then in your main header file (MyPlugin.h or whatever your plugin is named) you prototype the accessor functions:

void SetTest(bool t);
bool GetTest(void);

Then you simply include the main header file in each .cpp file where you need access to the "test" variable:

#include "MyPlugin.h"
//......
  
if(GetTest())
{
     // do something
}

Adios,
Cactus Dan

On 12/10/2013 at 09:29, xxxxxxxx wrote:

thank you very much for the input.. 
still get the following error message:

1>  myPlugin.cpp
1>myPlugin.obj : error LNK2001: unresolved external symbol "int __cdecl getTest(void)" ([email protected]@YAHXZ)
1>C:\Program Files\MAXON\CINEMA 4D R14\plugins\myPlugin\myPlugin.cdl64 : fatal error LNK1120: 1 unresolved externals

the thread i mentioned earlier said it is some problem with the linker. and since all those tests result in the same error i guess it must be some general setting i am missing??

EDIT: my fault. i mixed a uppercase letter now working. many thanks !

On 12/10/2013 at 09:36, xxxxxxxx wrote:

Howdy,

Did you forget to include the header?

Adios,
Cactus Dan

On 12/10/2013 at 09:37, xxxxxxxx wrote:

..no, it was a typo... now working

On 12/10/2013 at 09:45, xxxxxxxx wrote:

Howdy,

Ah! Glad it's working for you.

Adios,
Cactus Dan

On 12/10/2013 at 09:46, xxxxxxxx wrote:

i am happy, too, since this helped me solve the thing with my demo version of the plugin, too

On 14/10/2013 at 12:06, xxxxxxxx wrote:

It's quite easy as Niklas suggested.

In your main.cpp:

  
bool your_global_variable = false;  
  
PluginStart()  
{  
  your_global_variable = true;  
}  

In any other file (e.g. myPlugin.h) :

  
extern bool your_global_variable;  
  
int any_function(int a, int b) //or anywhere else in this file  
{  
  //do something with your_global_variable  
  return your_global_variable ? (a + b) : (a - b);  
}  

You don't need to include any file anywhere. You just need the declarations to make the scope see it.

Originally posted by xxxxxxxx

thank you. i tried this but still i must do something wrong.

in the main.cpp i have #include "myPlugin.h"

and in myPlugin.h i have

#ifndef _myPlugin_H_
#define _myPlugin_H_

extern int myTest;

enum
{
 ...

when i try to compile i get the following error:
[quote]
1>  Main.cpp
1>  myPlugin.cpp
1>     Creating library C:\Program Files\MAXON\CINEMA 4D R14\plugins\myPlugin\obj\myPlugin\x64_Debug\myPlugin.cdl64.lib and object C:\Program Files\MAXON\CINEMA 4D R14\plugins\myPlugin\obj\myPlugin\x64_Debug\myPlugin.cdl64.exp
1>Main.obj : error LNK2001: unresolved external symbol "int myTest" ([email protected]@3HA)
1>myPlugin.obj : error LNK2001: unresolved external symbol "int myTest" ([email protected]@3HA)
1>C:\Program Files\MAXON\CINEMA 4D R14\plugins\myPlugin\myPlugin.cdl64 : fatal error LNK1120: 1 unresolved externals

i found this thread http://stackoverflow.com/questions/7004031/c-unresolved-externals but i dont understand what i need to do now...
[/QUOTE]