LeafLabs Garden » Topic: passing a class method pointer as a function pointer

LeafLabs Garden » Topic: passing a class method pointer as a function pointer http://forums.leaflabs.com/topic.php?id=11679 A place to share, learn, and grow... en-US Fri, 22 Jan 2016 00:14:04 +0000 http://bbpress.org/?v=1.0.2 <![CDATA[Search]]> q http://forums.leaflabs.com/search.php bubulindo on "passing a class method pointer as a function pointer" http://forums.leaflabs.com/topic.php?id=11679#post-26047 Thu, 16 May 2013 06:56:46 +0000 bubulindo 26047@http://forums.leaflabs.com/ Yes, that seems to be the solution. I'll leave the revolution counting bit out of the library for now. I should have a working version in two weeks (after my vacation). :) mlundinse on "passing a class method pointer as a function pointer" http://forums.leaflabs.com/topic.php?id=11679#post-26046 Thu, 16 May 2013 05:53:59 +0000 mlundinse 26046@http://forums.leaflabs.com/ Use a global that is set somewhere, you can even let the timer handler switch the current Encoder to the next object of an array of objects: gCurrentEncoder * Encoder; And then let your interrupthandler be: void my_timer_handler() { gCurrentEncoder->timer_interrupt_handler(); /* Determine whitch Encoder object to call next ?? */ } bubulindo on "passing a class method pointer as a function pointer" http://forums.leaflabs.com/topic.php?id=11679#post-26045 Thu, 16 May 2013 05:24:13 +0000 bubulindo 26045@http://forums.leaflabs.com/ Ok... Thanks for the help. Guess the revolution counter will have to be done somewhere else then. :( mlundinse on "passing a class method pointer as a function pointer" http://forums.leaflabs.com/topic.php?id=11679#post-26044 Thu, 16 May 2013 05:10:51 +0000 mlundinse 26044@http://forums.leaflabs.com/ if the C function can call to a memeber, the that call is even less possible from inside the timer interrupt handler. There is no current Encoder object "this" in the interrupt handler context, so your approach doesnt work. Your mtehod must be called like anEncoderObject.timer_interrupt_handler() and there is no way to pass the encoder object instance to the timer interrupt handler. If you have several encoder objects, how should the handler know which to select ? If you only got one then use a C adapter class. The error message simply says that your class method is not possible to use as a C void func void. bubulindo on "passing a class method pointer as a function pointer" http://forums.leaflabs.com/topic.php?id=11679#post-26043 Thu, 16 May 2013 03:33:15 +0000 bubulindo 26043@http://forums.leaflabs.com/ @mlundinse Not sure that is possible. The C function can't call a method that hasn't been instantiated... Since this is a general library, that may be a problem as I can't instantiate all timers as encoders. I think the solution might be a two level approach where the C++ code is just a wrapper of the C functions. :\ I really hate doing it like this as it defeats the purpose. :( Edit: Thinking a bit more about it and a two level approach isn't efficient as I would increment/decrement one variable in a C file, but I can use 4 (on a Maple) timers as encoders. That would mess the whole thing up, or creating one of each for the possibility of the timers being used as an encoder is not great either. :\ Crap. :( bubulindo on "passing a class method pointer as a function pointer" http://forums.leaflabs.com/topic.php?id=11679#post-26042 Thu, 16 May 2013 03:26:28 +0000 bubulindo 26042@http://forums.leaflabs.com/ Hello again, my timer interrupt is this: void Encoder::timer_interrupt_handler(){ if (this->Direction() == POSITIVE) _revolutions++; if (this->Direction() == NEGATIVE) _revolutions--; } And I try to attach it to the timer as this: timer_attach_interrupt(_TIMER, TIMER_UPDATE_INTERRUPT, timer_interrupt_handler); I get this error: Also note that because of preprocessing, line numbers won't match up exactly. We're working on a fix. /Users/bubulindo/Documents/MapleIDE/libraries/Encoder/encoder.cpp: In constructor 'Encoder::Encoder(timer_dev*, unsigned char, unsigned int, unsigned int)': /Users/bubulindo/Documents/MapleIDE/libraries/Encoder/encoder.cpp:104: error: argument of type 'void (Encoder::)()' does not match 'void (*)()' Casting gives me a similar error, if I try this: timer_attach_interrupt(_TIMER, TIMER_UPDATE_INTERRUPT, (voidFuncPtr)timer_interrupt_handler); I get this error: Also note that because of preprocessing, line numbers won't match up exactly. We're working on a fix. /Users/bubulindo/Documents/MapleIDE/libraries/Encoder/encoder.cpp: In constructor 'Encoder::Encoder(timer_dev*, unsigned char, unsigned int, unsigned int)': /Users/bubulindo/Documents/MapleIDE/libraries/Encoder/encoder.cpp:104: error: invalid use of member (did you forget the '&' ? Any thoughts? mlundinse on "passing a class method pointer as a function pointer" http://forums.leaflabs.com/topic.php?id=11679#post-26029 Wed, 15 May 2013 13:28:41 +0000 mlundinse 26029@http://forums.leaflabs.com/ The timer_attach_interupt expects a 'normal C' function pointer to a void function of a void argument. Now a C++ class methods is a diferent creature, that sometimes can be called directly and sometimes looked up in Vtables from the class or parent classes. Your best bet is to write a small void function of void, C function, and pass this to the timer_attach_interrupt and then call your Encoder class method from inside this function. gbulmer on "passing a class method pointer as a function pointer" http://forums.leaflabs.com/topic.php?id=11679#post-26028 Wed, 15 May 2013 11:34:14 +0000 gbulmer 26028@http://forums.leaflabs.com/ bubulindo - Please post the text of the error messages and code for the things you have tried. (Preferably for the minimal case.) bubulindo on "passing a class method pointer as a function pointer" http://forums.leaflabs.com/topic.php?id=11679#post-26026 Wed, 15 May 2013 10:03:44 +0000 bubulindo 26026@http://forums.leaflabs.com/ Hello, I'm developing a class to use a timer as an encoder and am struggling with the timer interrupt. Basically I want the timer interrupt to increment/decrement a variable that will be the number of turns on the encoder. So inside the Encoder class I created a private method to do that (since the number of turns variable is private to the class), but when trying to pass a pointer of that method to the timer_attach_interrupt() it gives me an error that I can't seem to cast away (is this a pun?). Any ideas on how to solve this?