参数传递(varying parameters)

Ellipsis parameters are in C++ in order to compile C programs that use varargs . See your C compiler documentation for how to use varargs . Only simple data types from the C++ program should be passed to functions with ellipses parameters. In particular, objects of most class types are not copied properly when passed to ellipses parameters.

Ellipses parameters are used when it is impossible to list the type and number of all the arguments that might be passed to a function. Ellipses suspend type checking. Their presence tells the compiler that when the function is called, zero or more arguments may follow and that the types of the arguments are unknown. Ellipses may take either of two forms:

void foo(parm_list, ...);
void foo(...);

The first form provides declarations for a certain number of parameters. In this case, type checking is performed when the function is called for the arguments that correspond to the parameters that are explicitly declared, whereas type checking is suspended for the arguments that correspond to the ellipsis. In this first form, the comma following the parameter declarations is optional.

Most functions with an ellipsis use some information from a parameter that is explicitly declared to obtain the type and number of optional arguments provided in a function call. The first form of function declaration with ellipsis is therefore most commonly used.