topic Re: library error with C++ application in MQX Software Solutions

library error with C++ application

OldNick — Thu, 28 Jul 2011 15:58:50 GMT

Sorry if I have already posted this, but I am gettting hopelessly confused...just trying to add a simple C++ file to one of the standard MQX-towerK40 examples (hello.ewp)

IAR ewarm 6.2, project settings exactly as supplied, with one change - compiler c or c++ "Auto" (based on extension)

C++ version is EEC++

#include <iostream>
#include <mqx.h>
#include <bsp.h>

void printstring(void)
{
cout<<"hello"<<endl;
}

The simple act of adding this file to the build (even if you never call printstring() !) causes the linker to warn about there being no heap.

If I add the operator overloads to the cpp file in the same way that the PEG++ librar build uses (which DOES work with MQX), the project compiles and links with 0 errors 0 warnings.

But the debugger never gets to main.

Does anybody know what is going on?

PS> There are a bunch of similar questions in th ancient history on this forum, but I haven't seen that anybody had it answered yet. It would be nice if there was a FAQ on how to make C++ apps work with MQX, or at least make it clear that it can't be done.

Re: library error with C++ application

KJFPE — Fri, 29 Jul 2011 15:57:07 GMT

If you plase the following in your klinker file

define block HEAP with size = 0x2000, alignment = 8{ };

place in RAM_region {block HEAP};

it will work

Re: library error with C++ application

OldNick — Mon, 01 Aug 2011 18:17:19 GMT

KJFPE wrote:
Hi

If you plase the following in your klinker file

define block HEAP with size = 0x2000, alignment = 8{ };
place in RAM_region {block HEAP};

it will work

it might work, but is it safe?

MQX does all its own memory management (I think).

Let's say we need to kill the C++thead due to an RTOS error. What happens to cout if it is on the heap? There is no explicit malloc. for cout...can cout be deleted? Looks like a recipe for a memory leak?

My belief is that a C++ thread should be able to be written that runs in MQX without having an externally defined heap. I know that this can be done because PEG+ is integrated with MQX and runs (we already discussed this). But PEG+ might not use stdio libraries so might avoid this issue by "accident"?

Since MQX insists on taking over the whole processor, startup code, IO pins, timers, device drivers etc. it would be kind of good to know the limitations of a mixed language environment.

In the more general case, I am simply looking for a way to configure either complier or linker or both which permits C++ application code to run on top of MQX as if MQX were a C++ RTL, but safely.

the fallback position is to abandon C++ altogether and try to write object oriented "C". ( (void *) pthis->do_stuff(void * paramset )

It works, but is it a good idea?