"Actually i am making a multi-tasking kernel for p87c51RD+. For that purpose i feel it is easy to write the code in C++ instead of C."

I think you are making the wrong decision. While C++ definitely has a role as a programming language in some situations, the jury is still out as to whether is is appropriate under any circumstances in embedded systems, especially 8 bitters. One area where even 'C' might not be appropriate, never mind C++, would be coding a multitasking kernel. Many consider a multitasking kernel itself to be inappropriate.

If you are doing this as an academic exercise then fine, otherwise you are reinventing a possibly square wheel with a very large hammer.