What are the automatic type promotions of variadic function arguments?

Question

Consider the following code snippet:

#include 
#include 

void display(int num, ...) {
    char c;
    int j;
    va_list ptr;         


        

Answer 1

another case that the others forgot to mention are pointer types, critical is NULL in particular. Since this could expand to 0 or (void*)0 (or some other weird things) you will not know if the compiler puts an int or a void* in the list. Since these can have different width, this can lead to annoying bugs.

Answer 2

While using va_arg the char is promoted to int. There are other types(the list given by @R..) which are promoted.

so in order to read it as a char you have to do typecast.

like: c = (char) va_arg(ap, int);

for the complete example please see:

http://en.cppreference.com/w/cpp/language/variadic_arguments

Answer 3

You can use any standard type with va_arg except char, signed char, unsigned char, short, unsigned short, _Bool, and float. It's possible that an implementation defines additional nonstandard types that also have integer conversion rank lower than int, or likewise nonstandard small floating-point types, but you would not need to be aware of these unless you intend to use them, so for practical purposes the list I gave is complete.