A union is a data structure that stores several different types of data at the same single location in memory. Although this might sound like madness in a garbage collected world many older binary data formats still heavily rely on this. A possible use is if you want to modify an IPv4 address. An IPv4 address is 4 bytes, or an unsigned C# int. You might want to manipulate the IP address as a single value, or by splitting it into four separate bytes.

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