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)

[edit] 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.

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

[edit] Example 1

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

Output:

Hello, World!