Sprintf比打印占用更多的空间？

Question

I'm doing an Arduino sketch and I'm trying to gain some space. I saw on some websites that it's better to use sprintf than print . I tried but it takes way more space.

For example :

  char toWrite[18];
  sprintf(toWrite,"%d/%d/%d %d:%d:%d",RTC.now().day(),RTC.now().month(),RTC.now().year()-2000,RTC.now().hour(),RTC.now().minute(),RTC.now().second());
  tft.println(toWrite);

takes more space than :

  tft.print(RTC.now().day(), DEC);
  tft.print('/');
  tft.print(RTC.now().month(), DEC);
  tft.print('/');
  tft.print(RTC.now().year(), DEC);
  tft.print(' ');
  tft.print(RTC.now().hour(), DEC);
  tft.print(':');
  tft.print(RTC.now().minute(), DEC);
  tft.print(':');
  tft.println(RTC.now().second(), DEC);
  tft.println();

Could someboby explain me why ?

Many thanks !

PS : Sorry for my English, it's not my mother tongue =)

Answer 1

The routine sprintf is larger because it is a more complicated (and more flexible) routine than print. You can make your code smaller by having more arduous print statements. Unfortunately, there is no free lunch in this case.

Answer 2

You can really cut down printf if you remove the extraneous formats.
Here is an example alternate fprintf (printf is just fprintf with 1 as first arg) that compiles down to 1/2kb including my conversion functions (it could be smaller if you remove more)

void myfprintf_(int fd,int nargs, ...){ 
   va_list ap; va_start(ap, nargs); static char *s; const char *fmt; 
   fmt=va_arg(ap, char *); 
   int i=0,p; 
   char buf[80]; 
while (fmt[i]){ 
   p=0; 
   while (fmt[i]!='%' && fmt[i]!=0) buf[p++]=fmt[i++]; 
   if (p != 0) write(fd,buf,p); 
   if (nargs-->0){ 
      switch (fmt[++i]) { 
      case 's': s=va_arg(ap, char *); break; 
      case 'd': s=dtos(va_arg(ap, int)); break; 
      case 'x': s=dtox(va_arg(ap, int),'a'); break; 
      case 'X': s=dtox(va_arg(ap, int),'A' ); break; 
      case 'f': s=ftos(va_arg(ap, double)); break; 
      case 'c': buf[0]=(va_arg(ap, int));buf[1]=0;s=buf;break; 
      case '%': s="%"; break; 
      default : s="";break; 
      } write(fd,s,strlen(s)); 
   } 
i++; 
} 
va_end(ap); 
}

just comment out the formats you won't need and modify for your existing conversion functions - Also if you want it to be more compliant, make it an int function vs void and sum the returns of write for the return value ... though 99% of the time I don't use printf's return.