Offset a void pointer

Hi

I have little question
It seems impossible to me to offset a void pointer with the += operator
can someone explain me why ?
I don t really understand the compiler here ... the left casting should
give him the memory unit size , right?Is left casting forbidden?

void *BufferPtr;
unnsigned int stridde=5;
//doesnt compile !
(char*)BufferPtr+=stride;
//will compile
BufferPtr=(char*)BufferPtr+stride;

Thanks 
GC.


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