OpenEuphoria

1. Cannot use 'call_back' for a procedure

• Posted by ArthurCrump Aug 27, 2010
• 1319 views

I want to use call_back(routine_id("procedure_name")) but Euphoria refuses to use call_back on a procedure and insists on a function or type.

An error handler can be specified for the FreeImage library.
The error handler should be specified with a VOID result.
In Euphoria that is a procedure, not a function.
The error handler is registered to FreeImage using FreeImage_SetOutputMessage
requiring the machine address of the error handler.
Unfortunately, call_back only seems to work with functions and types.
When the error handler is specified as a procedure Euphoria reports an error.
On the other hand, if the error handler is specified as a function, the program disappears on returning from the error handler.
At present a win32lib abortErr(...) is used and shows the appropriate error message from FreeImage.
How can I get it to register a procedure as the error handler?

Arthur

3. Re: Cannot use 'call_back' for a procedure

• Posted by ArthurCrump Aug 27, 2010
• 1254 views

Thank you; I will try that tomorrow.

5. Re: Cannot use 'call_back' for a procedure

• Posted by jimcbrown (admin) Aug 28, 2010
• 1285 views

I've updated a new dll based on your response below, and it is available at http://malcom.unkmar.com/lostsouls/testfi.dll

Here is the source:

int(*void_call_back_1_func)(int x, const char * y); 
int(*void_call_back_2_func)(int x, const char * y); 
int(*void_call_back_3_func)(int x, const char * y); 
int(*void_call_back_4_func)(int x, const char * y); 
int(*void_call_back_5_func)(int x, const char * y); 
 
void set_call_back_1(int(*f)(int x, const char * y)) 
{ 
	void_call_back_1_func = f; 
} 
 
void void_call_back_1(int x, const char * y) 
{ 
	void_call_back_1_func(x, y); 
} 
 
void set_call_back_2(int(*f)(int x, const char * y)) 
{ 
	void_call_back_2_func = f; 
} 
 
void void_call_back_2(int x, const char * y) 
{ 
	void_call_back_2_func(x, y); 
} 
 
void set_call_back_3(int(*f)(int x, const char * y)) 
{ 
	void_call_back_3_func = f; 
} 
 
void void_call_back_3(int x, const char * y) 
{ 
	void_call_back_3_func(x, y); 
} 
 
void set_call_back_4(int(*f)(int x, const char * y)) 
{ 
	void_call_back_4_func = f; 
} 
 
void void_call_back_4(int x, const char * y) 
{ 
	void_call_back_4_func(x, y); 
} 
 
void set_call_back_5(int(*f)(int x, const char * y)) 
{ 
	void_call_back_5_func = f; 
} 
 
void void_call_back_5(int x, const char * y) 
{ 
	void_call_back_5_func(x, y); 
} 

And here is some example code:

include std/dll.e 
 
atom testfi = open_dll("testfi.dll") 
atom callbackptr = define_c_var(testfi, "void_call_back_1") 
atom set_callback = define_c_proc(testfi, "set_call_back_1", C_POINTER) 
 
c_proc(set_callback, {call_back(routine_id("FreeImageErrorHandler"))}) 
 
c_proc(xfiSetOutputMessage,{callbackptr}) 

This was tricky to figure out because the first parameter of FreeImageErrorHandler is an enum, which does not have a defined bit size. (On most C compilers, it's usually the same size as an int, but this is not guaranteed.)

c_proc(xfiSetOutputMessage,{call_back(routine_id("FreeImageErrorHandler"))}) 
 

Other than the trickiness with enum bitsizes, there is nothing unusual or tricky about FreeImage's SetOutputMessage function or the FreeImage_OutputMessageFunction.

I wonder if you are using 3.11 and have DEP enabled. That would cause the sort of crash you are seeing, and it would occur on any time of call_back, not just void function call_backs.

7. Re: Cannot use 'call_back' for a procedure

• Posted by ArthurCrump Aug 29, 2010
• 1142 views

I tried testfi.dll and realised, after a time, that I needed

	c_proc(xfiSetOutputMessage,{peek4u(callbackptr)})  
 

That got it into the error handler and I could show the error message, but the program still disappears when it returns to FreeImage.
I will concentrate on the rest of the routine and its documentation for now and leave the error handler until later.

Thank you for you interest in this; you have been most helpful.

Arthur