How to print binary number via printf

Question

Possible Duplicate:
Is there a printf converter to print in binary format?

Here is my program

#include<stdio.h>
int main ()
{
    int i,a=2;
    i=~a;
    printf("a=%d\ni=%d\n",a,i);
    return 0;
}

The output is

a=2
i=-3

I want this to print in binary. There are %x, %o, and %d which are for hexadecimal, octal, and decimal number, but what is for printing binary in printf?

Solution 1

printf() doesn't directly support that. Instead you have to make your own function.

Something like:

while (n) {
    if (n & 1)
        printf("1");
    else
        printf("0");
    n >>= 1;
}
printf("\n");

Solution 2

Although ANSI C does not have this mechanism, it is possible to use itoa() as a shortcut:

  char buffer [33];
  itoa (i,buffer,2);
  printf ("binary: %s\n",buffer);

Here's the origin:

itoa in cplusplus reference

It is non-standard C, but K&R mentioned the implementation in the C book, so it should be quite common. It should be in stdlib.h.

Comments

[cnicutar]

stackoverflow.com/questions/111928/…

[Kerrek SB]

Do you really want binary? Hexadecimal is often just as good (or even better), as it maps every 4 bits into one hex-digit, giving you both a compact and expressive representation of the binary data.

[Vinicius Kamakura]

@Kerrek are you really saying that seeing a number in it's binary representation is useless? Try analyzing a float number in hex digits :P

[Kerrek SB]

@hexa: Yep, doing that all the time. I wrote a ULP comparer for long doubles, which I gladly debugged in hex. Hex really is just binary compressed a little.

[C.D.H.]

binary can be useful for looking at how bitwise memory maps are set, if they are documented accordingly and you want to look at the values laid out the same way as in the document. lets not bust anyone's chops for wanting their data in whatever format suits their needs most.

[David Heffernan]

This prints the binary representation backwards

[kapilddit]

@David Heffernan How can we write which support both plateform 32bit and 64bit.

[kapilddit]

@hexa make function & use recursion to correct the printing order.will it be helpful?

[evandrix]

in case <stdlib.h>/<cstdlib> is not working for you, here's a quick roll-your-own implementation @ strudel.org.uk/itoa

[jww]

@kapilddit - why in the world would you try to add your answer to Hexa's answer? You've been around long enough to know how Stack Overflow works.

[danijar]

Corrected via recursion stackoverflow.com/a/27627015/1079110.

[luart]

Outlined conversion can't be used multiple times inside complex printf() and is not efficient (multiple calls to printf). Here is one statement standard and generic solution: stackoverflow.com/a/31660310/1814353

[brita_]

For correct order use and any type use: template <typename T> void print_binary(T n) { int numbits = sizeof(T) * 8; while(--numbits >= 0) printf("%c", (n & ((T)1<<numbits)) ? '1' : '0'); } For C only with an hardcoded data type, replace all 'T' by eg.'int'.

[choppe]

if n is not an unsigned integer, this loop will print for ever.

[71GA]

Note that printf() in this case is an extremely large overhead. You should instead use putc(). It will greatly increase performance.