Dear Sir, I wanted to use thread safe functions in free rtos.But I am not able to use reentrant version of strtok i.e strtokr in my application program.I am using heap4.c.Please help in sorting out this problem for usage of strtok_r in my application

You don’t say which compiler you are using, and give no clue as to what “unable to use” means, but in any case, strtok_r will be provided by your library, not by FreeRTOS.