Function declarations
A function identifier preceded by its return type and followed by its parameter list is called a function declaration or function prototype. The prototype informs the compiler of the format and existence of a function prior to its use. The compiler checks for mismatches between the parameters of a function call and those in the function declaration. The compiler also uses the declaration for argument type checking and argument conversions.
Implicit declaration of functions is not allowed: you must explicitly declare every function before you can call it.
If a function declaration is not visible at the
point at which a call to the function is made, the compiler assumes
an implicit declaration of extern int func();
However,
for conformance to C99, you should explicitly prototype every function
before making a call to it.
- Function storage class specifiers, which specify linkage
- Function return type specifiers, which specify the data type of a value to be returned
- Function specifiers, which specify additional properties for functions
- Function declarators, which include function identifiers as well as lists of parameters
All function declarations have the form:
Function declaration syntax
auto
. For more information about trailing return
type, see Trailing return type (C++11).