The same as [sec:sf_alloc]sf_alloc but it allocates new memory such that it appends the block previously assigned by sf_alloc. It takes three parameters, first one is a void pointer to the old memory block. Second and third parameters are the same as for sf_alloc but are used to determine the new block, which is to be appended.
sf_realloc returns a void pointer pointing to the whole memory block (new + old).