9 Declarations [dcl.dcl]

9.5 Function definitions [dcl.fct.def]

9.5.1 General [dcl.fct.def.general]

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function-body:
ctor-initializer compound-statement
function-try-block
= default ;
deleted-function-body
deleted-function-body:
= delete ;
= delete ( unevaluated-string ) ;
Any informal reference to the body of a function should be interpreted as a reference to the non-terminal function-body, including, for a constructor, default member initializers or default initialization used to initialize a base or member subobject in the absence of a mem-initializer-id ([class.base.init]).
The optional attribute-specifier-seq in a function-definition appertains to the function.
A function-definition with a requires-clause shall define a templated function.
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In a function-definition, either void declarator ; or declarator ; shall be a well-formed function declaration as described in [dcl.fct].
A function shall be defined only in namespace or class scope.
The type of a parameter or the return type for a function definition shall not be a (possibly cv-qualified) class type that is incomplete or abstract within the function body unless the function is deleted ([dcl.fct.def.delete]).
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[Example 1: 
A simple example of a complete function definition is int max(int a, int b, int c) { int m = (a > b) ? a : b; return (m > c) ? m : c; }
Here int is the decl-specifier-seq; max(int a, int b, int c) is the declarator; { /* ... */ } is the function-body.
— end example]
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A ctor-initializer is used only in a constructor; see [class.ctor] and [class.init].
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[Note 1: 
A cv-qualifier-seq affects the type of this in the body of a member function; see [expr.prim.this].
— end note]
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[Note 2: 
Unused parameters need not be named.
For example,
void print(int a, int) { std::printf("a = %d\n",a); } — end note]
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A function-local predefined variable is a variable with static storage duration that is implicitly defined in a function parameter scope.
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The function-local predefined variable __func__ is defined as if a definition of the form static const char __func__[] = "function-name"; had been provided, where function-name is an implementation-defined string.
It is unspecified whether such a variable has an address distinct from that of any other object in the program.82
[Example 2: struct S { S() : s(__func__) { } // OK const char* s; }; void f(const char* s = __func__); // error: __func__ is undeclared — end example]
82)82)
Implementations are permitted to provide additional predefined variables with names that are reserved to the implementation ([lex.name]).
If a predefined variable is not odr-used ([basic.def.odr]), its string value need not be present in the program image.