FreeRTOS, C++ and xTaskCreate() function

Kernel
1

anonymous wrote on Sunday, November 03, 2013:

Hi!

I try to create a C++ application (and C++ tasks) based on FreeRTOS but I can not call the xTaskCreate() function from my C++ code.

Default FreeRTOS main() function:

/* default FreeRTOS main() */

int main( void )
{
    prvSetupHardware();
    /* Exported C++ function */
    runTask();
    ...
}

Below the header and source files based on the following both examples:

http://sourceforge.net/p/freertos/discussion/382005/thread/5d5201c0
http://interactive.freertos.org/entries/223648-using-freertos-with-c

I think I have included all relevant C-header files in my C++ header:

#ifdef __cplusplus
extern "C" {
#endif
#include <FreeRTOS.h>
#include <task.h>
#ifdef __cplusplus    
}
#endif

… and my C/C++ wrapper functions:

#ifdef __cplusplus
extern "C" {
#endif
void tskWrp(void* p);
void runTask();
#ifdef __cplusplus
}
#endif

C++ source file: prl_task.cc

/* C++ source file: prl_task.cc /*   

/*-----------------------------*/
/* 2 simple tasks */

void vTask1( void ) {
    doSomething();
}

void vTask2( void ) {
    doSomething();
}

/*------------------------------*/
/* base class CTask */

CTask::CTask(char const* name,
	unsigned portBASE_TYPE priority,
	unsigned portSHORT stackDepth=1000) {
    
    /* Code works up to here! */    
    //vTask1();
    xTaskCreate(&tskWrp, (signed char*)name, 1000, this, 1, NULL);
}

void CTask::Task() {

 vTask1();
}
/*-------------------------------*/
/* derived class CTask1 */

CTask1::CTask1(char const* name,
            unsigned portBASE_TYPE priority,
	unsigned portSHORT stackDepth=1000) : CTask(name, priority,stackDepth) {
}

void CTask1::Task() {

 vTask2();
}

/*--------------------------------*/ 
/* interface functions C C++ */

void runTask(){

    CTask1 task("tsk",1,1000);
}

/*--------------------------------*/
/* wrapper function */

void tskWrp(void* p) {

(static_cast<CTask*>(p))->Task();
}

I can compile the code without errors but the xTaskCreate() function will be “ignored” and the program is not running on my MPU. If I call directly another functions e.g. vTask1() instead of xTaskCreate() the program works fine on the MPU.

By the way my IDE throws a warning “Function ‘xTaskGenericCreate’ could not be resolved”. I’m not sure whether the IDE warning or any other reason is the cause of my problem.

Maybe someone can help me?

Florian

2

richard_damon wrote on Sunday, November 03, 2013:

First, you shouldn’t need the #ifdef __cplusplus lines to add the extern “C” stuff, as that should be in the headers already.

The other thing to note it that the FreeRTOS files MUST be compelled a C files, not C++ files, or they won’t work right, The extern “C” stuff in the headers sets up the linkage properly for the cross language link. That might explain the could not be resolved problem.

3

anonymous wrote on Sunday, November 03, 2013:

If I will create a C-compiled freeRTOS.o object file and a C++ compiled application.o object file, is it possible to link both together by using g++?

The following link recommends to use g++ for the linking process in case ob mixing C and C++:

http://www.parashift.com/c++-faq/overview-mixing-langs.html

4

richard_damon wrote on Sunday, November 03, 2013:

Yes, you should be able to link files compiled as C and files compiled as C++, that is the main purpose of the extern “C” syntax. As the link suggests, main should be C++, the libraries used should be C++, so the linker should generally be the C++ linker. The C compiler needs to be ABI complient with the C++ compiler.