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Manipulating data via its address. Indirection is a powerful and general programming technique. It can be used for example to process data stored in a sequence of consecutive memory locations by maintaining a pointer to the current item and incrementing it to point to the next item.
Indirection is supported at the machine language level by indirect addressing. Many processor and operating system architectures use vectors which are also an instance of indirection, being locations which hold the address of a routine to handle a particular event. The event handler can be changed simply by pointing the vector at a new piece of code.
C includes operators "&" which returns the address of a variable and its inverse "*" which returns the variable at a given address.