printf() question in serial communications

Projects Programming
1

I am doing a little project by using serial com.
I got this part of code written to print strings (source:Arduino Playground - Printf)

#include <stdarg.h>
void p(char *fmt, ... ){
        char tmp[128]; // resulting string limited to 128 chars
        va_list args;
        va_start (args, fmt );
        vsnprintf(tmp, 128, fmt, args);
        va_end (args);
        Serial.print(tmp);
}
loop(){
unsigned long a=0xFFFFFFFF;
p("Decimal a: %l\nDecimal unsigned a: %lu\n", a, a); 
p("Hex a: %x\n", a);}

but when I updated it to UNO, it always returned,

Decimal a:?
Hex a:?

what's wrong? Thanks!

2

You need %li %lu and %lx - it works for me.