6.12. Functions with Empty Parameter Lists

In C++, an empty parameter list is specified by writing either void or nothing at all in parentheses. The prototype

void print();

specifies that function print does not take arguments and does not return a value. Figure 6.16 demonstrates both ways to declare and use functions with empty parameter lists.

Fig. 6.16. Functions that take no arguments.

 1   // Fig. 6.16: fig06_16.cpp
 2   // Functions that take no arguments.
 3   #include <iostream>
 4   using std::cout;
 5   using std::endl;
 6
 7   void function1(); // function that takes no arguments      
 8   void function2( void ); // function that takes no arguments
 9
10   int main()
11   {
12      function1(); // call function1 with no arguments
13      function2(); // call function2 with no arguments
14      return 0; // indicates successful termination
15   } // end main
16
17   // function1 uses an empty parameter list to specify that
18   // the function receives no arguments
19   void function1()
20   {
21      cout << "function1 takes no arguments" << endl;
22   } // end function1
23
24   // function2 uses a void parameter list to specify that
25   // the function receives no arguments
26   void function2( void )
27   {
28      cout << "function2 also takes no arguments" << endl;
29   } // end function2

function1 takes no arguments
function2 also takes no arguments

Portability Tip 6.2

The meaning of an empty function parameter list in C++ is dramatically different than in C. In C, it means all argument checking is disabled (i.e., the function call can pass any arguments it wants). In C++, it means that the function explicitly takes no arguments. Thus, C programs using this feature might cause compilation errors when compiled in C++.

Common Programming Error 6.13

C++ programs do not compile unless function prototypes are provided for every function or each function is defined before it is called.