function terminology

Arguments vs parameters

• Parameters: what the function expects (as seen from the inside).

• Arguments: what the function is given (as seen from the outside).

Thus:

• There is default arguments feature, not default parameters.

• Compilers may print an error that a given argument does not match specific parameter.

Type vs prototype vs signature

Briefly:

• Signature: information which differentiates the function from others when overloading.

• Type: Every object and function has a type. The most significant application are function pointers.

• Prototype: Types of arguments (for compiler checks). C (until C23) allows to declare functions without prototype (empty parenthesis or old-style K&R syntax). In C, calling a function without prototype disables compile time checks and will invoke undefined behavior if the number of arguments doesn't match the number of parameters. In C++ it's not possible to declare a function without prototype. In C it's a common compiler setting to enable warnings on functions with missing prototype.

Prior to C++17, exception specification wasn't a part of function type. It was added to facilitate type system in more contexts - most notably now a function pointer can express it accepts only noexcept functions.