The void type, in several programming languages derived from C and Algol68, is the type for the result of a function that returns normally, but does not provide a result value to its caller. Usually such functions are called for their side effects, such as performing some task or writing to their output parameters. The usage of the void type in such context is comparable to that of the syntactic constructs which define subroutines in Visual Basic and procedures in Pascal. It is also similar to the unit type used in functional programming languages and type theory; however, there are some differences in allowable usage, in that the void type is taken to be an empty type with no values. See Unit type#In programming languages for a comparison.
C and C++ also support the pointer to void type (specified as void *), but this is an unrelated notion. Variables of this type are pointers to data of an unspecified type, so in this context (but not the others) void acts as a universal or top type. A program can convert a pointer to any type of data (except a function pointer) to a pointer to void and back to the original type without losing information, which makes these pointers useful for polymorphic functions.
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Famous quotes containing the words void and/or type:
“Soon silence will have passed into legend. Man has turned his back on silence. Day after day he invents machines and devices that increase noise and distract humanity from the essence of life, contemplation, meditation.... Tooting, howling, screeching, booming, crashing, whistling, grinding, and trilling bolster his ego. His anxiety subsides. His inhuman void spreads monstrously like a gray vegetation.”
—Jean Arp (1887–1948)
“One type of rice nourishes one hundred types of people.”
—Chinese proverb.