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digitalmars.D.learn - new class howto?

reply newbie <newbie nospam.com> writes:
hi,

why is it that one can not create a class with the following:

module A
extern (Windows):
uint  P_Start(char * pParam);
void  P_Stop();

module A
import A;

class XXX {
public:
  this() {}
  uint start(char *yy) {
    return  P_Start(yy);
  }
  void start(char *yy) {
    P_Stop();
  }
}


module C

 XXX tester = new XXX();


it will always generate an error during compilation:

      non-constant expression

when i try to do that in a function, then i will get an exception.
Jul 31 2007
next sibling parent newbie <newbie nospam.com> writes:
sorry, it should be


module A
extern (Windows):
uint  P_Start(char * pParam);
void  P_Stop();

module B
import A;

class XXX {
public:
  this() {}
  uint start(char *yy) {
    return  P_Start(yy);
  }
  void start(char *yy) {
    P_Stop();
  }
}


module C
import B;

XXX tester = new XXX();
Jul 31 2007
prev sibling next sibling parent reply Frits van Bommel <fvbommel REMwOVExCAPSs.nl> writes:
newbie wrote:

 module C
 
  XXX tester = new XXX();
 
 
 it will always generate an error during compilation:
 
       non-constant expression
 
 when i try to do that in a function, then i will get an exception.


You can only use constant expressions as initializers for global 
variables, so dynamic memory allocation is disallowed. To do what you 
want, use:
---
module C;

XXX tester;

static this() {
     tester = new XXX();
}
---
Jul 31 2007
next sibling parent newbie <newbie nospam.com> writes:
Frits van Bommel Wrote:


 newbie wrote:

 module C
 
  XXX tester = new XXX();
 
 
 it will always generate an error during compilation:
 
       non-constant expression
 
 when i try to do that in a function, then i will get an exception.


 
 You can only use constant expressions as initializers for global 
 variables, so dynamic memory allocation is disallowed. To do what you 
 want, use:
 ---
 module C;
 
 XXX tester;
 
 static this() {
      tester = new XXX();
 }
 ---


thank you for the reply.

it will compile, but it will fail with an exception.
that will also happen if i declare the variable in a function and than try to
do my new.

void testers() {
	  XXX tester = new XXX(); <---- exception
	  tester.Stop(); 
}

could it be, that the extern(Windows) is a problem?
Jul 31 2007
prev sibling parent reply newbie <newbie nospam.com> writes:
Frits van Bommel Wrote:


 newbie wrote:

 module C
 
  XXX tester = new XXX();
 
 
 it will always generate an error during compilation:
 
       non-constant expression
 
 when i try to do that in a function, then i will get an exception.


 
 You can only use constant expressions as initializers for global 
 variables, so dynamic memory allocation is disallowed. To do what you 
 want, use:
 ---
 module C;
 
 XXX tester;
 
 static this() {
      tester = new XXX();
 }
 ---


it is seeminglx not possible to call d functions or initialize d classes from a
function that is decorated with
extern(Windows)

extern (Windows) int WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
LPSTR lpCmdLine, int nCmdShow) {
	testery();
    DialogBox(hInstance, MAKEINTRESOURCE(IDD_DIALOG_MAIN), null, &Dialog_Main);
    return 0;
}


void testery() {
	  XXX testerx = new XXX;
	  testerx.Stop();
}


how does one call a D function or do a XXX testerx = new XXX; in such a
function?
Jul 31 2007
parent reply Daniel Keep <daniel.keep.lists gmail.com> writes:
newbie wrote:

 Frits van Bommel Wrote:
 

 newbie wrote:

 module C

  XXX tester = new XXX();


 it will always generate an error during compilation:

       non-constant expression

 when i try to do that in a function, then i will get an exception.


 You can only use constant expressions as initializers for global 
 variables, so dynamic memory allocation is disallowed. To do what you 
 want, use:
 ---
 module C;

 XXX tester;

 static this() {
      tester = new XXX();
 }
 ---


 it is seeminglx not possible to call d functions or initialize d classes from
a function that is decorated with
 extern(Windows)
 
 extern (Windows) int WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
LPSTR lpCmdLine, int nCmdShow) {
 	testery();
     DialogBox(hInstance, MAKEINTRESOURCE(IDD_DIALOG_MAIN), null, &Dialog_Main);
     return 0;
 }
 
 
 void testery() {
 	  XXX testerx = new XXX;
 	  testerx.Stop();
 }
 
 
 how does one call a D function or do a XXX testerx = new XXX; in such a
function?
 
 


Wait; you're calling this from WinMain?

The code you just supplied will not work because you haven't initialised
the garbage collector, nor run module ctors, nor run unittests.  See
http://digitalmars.com/d/windows.html for an example of what your
WinMain should look like.

	-- Daniel
Jul 31 2007
parent newbee <nospam nospam.com> writes:
Daniel Keep Wrote:


 
 
 newbie wrote:

 Frits van Bommel Wrote:
 

 newbie wrote:

 module C

  XXX tester = new XXX();


 it will always generate an error during compilation:

       non-constant expression

 when i try to do that in a function, then i will get an exception.


 You can only use constant expressions as initializers for global 
 variables, so dynamic memory allocation is disallowed. To do what you 
 want, use:
 ---
 module C;

 XXX tester;

 static this() {
      tester = new XXX();
 }
 ---


 it is seeminglx not possible to call d functions or initialize d classes from
a function that is decorated with
 extern(Windows)
 
 extern (Windows) int WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
LPSTR lpCmdLine, int nCmdShow) {
 	testery();
     DialogBox(hInstance, MAKEINTRESOURCE(IDD_DIALOG_MAIN), null, &Dialog_Main);
     return 0;
 }
 
 
 void testery() {
 	  XXX testerx = new XXX;
 	  testerx.Stop();
 }
 
 
 how does one call a D function or do a XXX testerx = new XXX; in such a
function?
 
 


 
 Wait; you're calling this from WinMain?
 
 The code you just supplied will not work because you haven't initialised
 the garbage collector, nor run module ctors, nor run unittests.  See
 http://digitalmars.com/d/windows.html for an example of what your
 WinMain should look like.
 
 	-- Daniel


that was the wright thing to do - thank you all so much.
Jul 31 2007
prev sibling parent "Stewart Gordon" <smjg_1998 yahoo.com> writes:
"newbie" <newbie nospam.com> wrote in message 
news:f8n64d$1bev$1 digitalmars.com...

 hi,

 why is it that one can not create a class with the following:

 module A
 extern (Windows):


You're missing the semicolon after the module name.

<snip>

 it will always generate an error during compilation:

      non-constant expression


On what compiler version are you getting that?  Please post compiler 
messages in full.

Stewart.
Aug 22 2007