Declaring functions

 

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A function declaration introduces the function name and its type. It may appear in any scope, and is commonly placed in header files.

ret name ( params ) cv ref except attr	(1)
auto name ( params ) cv ref except attr -> ret	(2)	(since C++11)

A function definition provides the body of a function. It may only appear in namespace or class scope.

attr decl name ( params ) cv ref except attr -> ret virt try init-list { body } catch	(3)
attr decl name ( params ) cv ref except attr -> ret virt = 0 ;	(4)
attr decl name ( params ) cv ref except attr -> ret virt = default ;	(5)	(since C++11)
attr decl name ( params ) cv ref except attr -> ret virt = delete ;	(6)	(since C++11)

Explanation

attr(C++11)	-	Optional sequence of any number of function attributes, such as [[noreturn]] or [[carries_dependency]]. May appear both before and after the function name
ret	-	the type returned by the function, may be void if the function returns nothing. Cannot be array or function type, although can be a pointer or reference to such. Required for all functions except constructors, destructors, and conversion operators, which must not provide a return type.
decl	-	declaration specifier sequence, which consists of none or some of the following keywords: static, extern, inline, virtual, explicit, friend, constexpr, combined with the return type, ret
cv	-	Optional const, volatile, or const volatile, only applicable to non-static member functions. For a member function of class T, the type of this will be const T*, volatile T*, or const volatile T* respectively. A member function declared const cannot modify members of *this.
ref(C++11)	-	Optional & or &&, only applicable to non-static member functions. For a member function of class T, the type of this will be T& or T&& respectively.
except	-	either dynamic-exception-specification or noexcept-specification
virt(C++11)	-	Optional override or final, only applicable to non-static member functions
->ret(C++11)	-	Trailing return type, only applicable if ret is auto. Useful if the type depends on argument names, such as template <class T, class U> auto add(T t, U u) -> decltype(t + u); or is complicated, such as in auto fpif(int)->int(*)(int)
init-list	-	Constructor initializer list, only used in constructors
try	-	Optional function try block. If present, catch must be provided
catch	-	Optional sequence of catch-blocks, only applicable of try is used.
body	-	The body of the function, a (possibly empty) compound statement
params	-	The list of parameters

Example 1

void function() {
   std::cout << "Hello, World!" << std::endl;
   //no return
}

Output:

Hello, World!