printing most sig byte...??

[myjay]

I have a pointer p that contains a valid address and am trying to print the MS 8 bits... since there isn't a way to do that in printf that i know of, i'm using a loop and it looks like...

 for(i=0; i<8; i++)
    {
      if(*p & 0x80)
        printf("1");
      else
        printf("0");

      *p<<1;

    }

however this either prints either 8 1's or 8 0's... I know that it's just not the way the numbers are b/c i have functions that print the numbers in decimal and hex and those work fine... any ideas?

John

[Hammer]

*p<<1;
Instead, try
*p <<= 1;

[myjay]

hmm, it says Bus error (core dumped) that's weird. considering it works fine if you print in hex or decimal

[myjay]

can you only perform shift operations on ints, can youdo them on chars?

John

[Dave_Sinkula]

How about something like this?

#include <stdio.h>
#include <limits.h>

void foo(void *a)
{
   union uType
   {
      void *p;
      unsigned char b [ sizeof(void*) ];
   } var;
   size_t i = sizeof(var.b)/sizeof(*var.b);
   var.p = a;
   printf("var.p  =  %p\n", var.p);
   do
   {
      size_t j = CHAR_BIT;
      printf("var.b[%lu]: ", (long unsigned)--i);
      do
      {
         putchar(var.b[i] & (1 << --j) ? '1' : '0');
      } while ( j );
      putchar('\n');
   } while ( i );
}

int main(void)
{
   int x = 42;
   foo(&x);
   return 0;
}

/* my output
var.p  =  0012FF88
var.b[3]: 00000000
var.b[2]: 00010010
var.b[1]: 11111111
var.b[0]: 10001000
*/

[Hammer]

Originally posted by myjay
hmm, it says Bus error (core dumped) that's weird. considering it works fine if you print in hex or decimal

Are you trying to run that code against an array or a string literal? If it's the latter, it won't work, as it modifies the data.

So, if you have this:
char *p = "blah";
change it to
char p[] = "blah";