C Interview Questions and Answers

 

I have a varargs function which accepts a float parameter

I have a varargs function which accepts a float parameter. Why isn't



va_arg(argp, float)



working?





In the variable-length part of variable-length argument lists, the old ``default
argument promotions'' apply: arguments of type float are always promoted
(widened) to type double, and types char and short int are promoted to int. Therefore,
it is never correct to invoke va_arg(argp, float); instead you should always use
va_arg(argp, double). Similarly, use va_arg(argp, int) to retrieve arguments which
were originally char, short, or int. (For analogous reasons, the last ``fixed''
argument, as handed to va_start, should not be widenable, either.)

Posted by:Richards