cpp/io/strstreambuf/setbuf

If is a null pointer and  is zero, this function has no effect.

Otherwise, the effect is implementation-defined: some implementations do nothing, while some implementations deallocate the dynamic member array used as the buffer and begin using the user-supplied character array of size, whose first element is pointed to by.

This function is protected virtual, it may only be called through or from member functions of a user-defined class derived from.