Is it possible to have a variadic function in C with no non-variadic parameter?

问题

I have the following function:

void doStuff(int unusedParameter, ...)
{
    va_list params;
    va_start(params, unusedParameter);
    /* ... */
    va_end(params);
}

As part of a refactor, I'd like to remove the unused parameter without otherwise changing the implementation of the function. As far as I can tell, it's impossible to use va_start when you don't have a last non-variadic parameter to refer to. Is there any way around this?

Background: It is in fact a C++ program, so I could use some operator-overloading magic as suggested here, but I was hoping not to have to change the interface at this point.

The existing function does its work by requiring that the variable argument list be null-terminated, and scanning for the NULL, therefore it doesn't need a leading argument to tell it how many arguments it has.

In response to comments: I don't have to remove the unused parameter, but I'd do it if there were a clean way to do so. I was hoping there'd be something simple I'd missed.

回答1:

Your choice is either leave it as it is and use va_list, alias it (if it's GCC) as others pointed out, or do something along the lines of exec(2) interface - passing an array of pointers requiring a NULL terminator:

/* \param args  NULL-terminated array of
 *              pointers to arguments.
 */
void doStuff( void* args[] );

Either way it would be much better to refactor the interface to somehow take advantage of the type system - maybe overload on exact argument types used:

void doStuff( int );
void doStuff( const std::string& );
void doStuff( const MyFancyAppClass& );

Hope this helps.

回答2:

In GCC, you have a workaround: You can define a macro with a variable number of arguments and then add the dummy parameter in the expansion:

#define doStuff(...) realDoStuff(0, __VA_ARGS__)

来源：https://stackoverflow.com/questions/2622147/is-it-possible-to-have-a-variadic-function-in-c-with-no-non-variadic-parameter

标签

variadic-functions