What is void in C?
What does void mean in C? I think it’s confusing to think of it having a singular meaning. It is part of a number of unrelated syntactic forms, and should be understood separately in each:
- As a return “type”. In the function declaration
void foo(int), thevoidsignifies that “foodoes not return a value”. - As a parameter type list. In the function declaration
char bar(void), thevoidsignifies that “barhas zero parameters”. - As the target “type” of a pointer. In the declaration
void* baz, thevoidsignifies that “bazpoints to a value of unknown type”.
It is confusing to call void a “type”. There are positions where a normal type (int) can be used, but void cannot. For example, int foo; is a valid declaration, but void foo; is not. There are also positions where void can be used, but a normal type cannot. For example, char foo(int) { return 'c'; } is not a valid function definition.
The standard calls void an “incomplete type”, but I find this unenlightening in the case of char bar(void).
Tagged . All content copyright James Fisher 2016. This post is not associated with my employer.
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