printf

[tbone]

I'm trying to write a printf function for my OS and it doesn't work,and I can't post it here because its too much.Can someone give me the code(I've tried the
fritzos code and the code from this site:http://my.execpc.com/~geezer/osd/libc/index.htm).

[Pype.Clicker]

i can offer some code, but it is quite unusual fasion while the lowest level deal with full strings (no putchar)

See SOSprint in sos32.asm,
_kprint_internal and kprint in display.c

...

[Pype.Clicker]

oh, and ... btw, if you have troubles with your PRINT function, just try to make it run in a Linux/Unix/window user process before you try it for real ...

[jrfritz]

Inorder for the FritzOS code to work...you need to include my whole header file...untill pk0.8 is released that is...since Pype convinced me to seperate headers and source ....

[mr. xsism]

[attachment deleted by admin]

[jrfritz]

Here's a nice tested printf...:

static int printf( char *msg, ... )
{
   char curchar = *msg;
   char* ch;
   char* str;

   va_list args;
   va_start( args, msg );

   // keep reading the message until it's the end of the message
   while ( curchar != '\0' )
   {
      // if it is just a character, then print
      if ( curchar >= ' ' && curchar != '%' )
      {
         putch( curchar );
      }

      // it's a '%'
      else if ( curchar == '%' )
      {
         // check ahead if it's another %
         // alot of help came from my compiler book;)
         ++msg;
         curchar = *msg;
         if ( curchar == '%' )
            putch( '%' );

         // not another % -- print the character, string, or number
         else
         {
            switch ( curchar )
            {
               case 'c':
                  *ch = ( unsigned char ) va_arg( args, int );
                  putch( *ch );
                  
                  break;

               case 's':
                  str = va_arg( args, char * );
                  printf( str );

                  break;

               case 'd':
                  // d = va_arg( args, int );
                  // code tk: itoa

                  break;

               default:
                  putch( '%' );      // just print % when it doesn't know
                           // what to do

                  break;
            }
         }
      }

      else if ( curchar == 0x08 || curchar == 0x09 || curchar == '\r' || curchar == '\n' )
      {
         putch( curchar );
      }

      ++msg;
      curchar = *msg;
   }

   va_end( args );
}

[rdragon]

I think you can clean that printf up a bit... here's the one i came up with so far...


void printf(const char* format, ...)
{
va_list list;
va_start(list, format);
   
int i = 0; //message index

while(format != 0x00)
{
if(format == '%')
{
switch(format[++i])
{
case '%': putchar('%'); break;
case 'c': putchar(va_arg(list, char)); break;
case 's': printf(va_arg(list, char*)); break;
case 'd': break;//integer, ick for now
default: printf("%%%c", format);
};
}
else
{
putchar(format);
}
i++;
}
}

it doesnt handle %d yet, and it will crash if you try to do something like printf("String:%s", "crash here->%s");

but other than that it works well for general purpose printing... by the standard, to output a single '%' you must enter "%%" (just like '\' and "\\")
also if you enter something weird like %z that it doesnt understand, it outputs what you typed (i.e. "%z" exactly as you gave it) not sure if that's standard, but i threw it in there

Tom you seem to be storing the arguments before you pass them to say, putch(), but there's no need, you can use putch() and as an argument, use the va_arg() macro

also, this part of your code:

else if ( curchar == 0x08 || curchar == 0x09 || curchar == '\r' || curchar == '\n' )
{
putch( curchar );
}

does absolutely nothing , in fact it wont ever get to that comparison, because this part of your code takes care of it:

if ( curchar >= ' ' && curchar != '%' )
{
putch( curchar );
}

[Pype.Clicker]

i would avoid recursive call of "printf" if i were you ... you're unlikely to love a stack overflow in a display function you'll use for debugging purpose.

Moreover, it's dangerous to do "printf(arg_list(char*))" to handle %s, because if the sub-string contains some %i, %d, %x, %s ... printf will try to translate them, but will get random values from arg_list as the recursive call has no arguments past the format string.

[rdragon]

i know... thats why I noted

it doesnt handle %d yet, and it will crash if you try to do something like printf("String:%s", "crash here->%s");

but yeah i threw it in there temporarily until i get around to writing a write_string() function or something that doesnt do formatting

[jrfritz]

I know about that...that was just a example...I don't really use a continual call to my printf.