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:
“The man Shelley, in very truth, is not entirely sane, and Shelley’s poetry is not entirely sane either. The Shelley of actual life is a vision of beauty and radiance, indeed, but availing nothing, effecting nothing. And in poetry, no less than in life, he is a beautiful and ineffectual angel, beating in the void his luminous wings in vain.””
—Matthew Arnold (1822–1888)
“Lise: Look, monsieur, I don’t know what type of girl you think I am, but I’m not. And now I would like to return to my friends.
Jerry: I thought you were bored with them. You sure looked it.
Lise: You should see me now.
Jerry: Ouch.”
—Alan Jay Lerner (1918–1986)