printf() and scanf() questions

The questions are about C95.



printf() questions:

1. printf() provides "%f" format specifier for double. Usually 
implemented as a variadic function how can it discern if the argument is 
float or double? Shouldn't we cast to double when passing a float value? 
If an implicit conversion takes place, at what stage does it take place? 
Consider as an example:

printf("%f\n", 123.45F);


2. The same question also applies when printing a signed char value with 
"%d" format specifier.



scanf() questions:

1. scanf() provides the "%f" specifier for float. How can it discern 
when we pass a double?


Example:

double x;

scanf("%f", &x);

If an implicit conversion to double takes place, at what stage does it 
take place? Also if such conversion takes place how it works when using 
a float variable?

Example:

float b;

scanf("%f", &b);