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memset is a range of data in an array that is initialized (the second point of initialization is a binary encoding)
memset 是初始化数组中的一段区域内的数据(初始化的第二点为2进制编码)
memcpy replaces the data in array b with the data in array a
memcpy是将b数组中的数据用a数组的数据替换
sizeof tells you the sizeof the array in bits
sizeof可以得出数组的大小(单位是bit)