Is there a printf converter to print in binary for

Question

I can print with printf as a hex or octal number. Is there a format tag to print as binary, or arbitrary base?

I am running gcc.

printf("%d %x %o\n", 10, 10, 10); //prints "10 A 12\n"
print("%b\n", 10); // prints "%b\n"

Answer 1

A small utility function in C to do this while solving a bit manipulation problem. This goes over the string checking each set bit using a mask (1<

void
printStringAsBinary(char * input)
{
    char * temp = input;
    int i = 7, j =0;;
    int inputLen = strlen(input);

    /* Go over the string, check first bit..bit by bit and print 1 or 0
     **/

    for (j = 0; j < inputLen; j++) {
        printf("\n");
        while (i>=0) {
            if (*temp & (1 << i)) {
               printf("1");
            } else {
                printf("0");
            }
            i--;
        }
        temp = temp+1;
        i = 7;
        printf("\n");
    }
}

Answer 2

No standard and portable way.

Some implementations provide itoa(), but it's not going to be in most, and it has a somewhat crummy interface. But the code is behind the link and should let you implement your own formatter pretty easily.

Answer 3

Here is a quick hack to demonstrate techniques to do what you want.

#include <stdio.h>      /* printf */
#include <string.h>     /* strcat */
#include <stdlib.h>     /* strtol */

const char *byte_to_binary(int x)
{
    static char b[9];
    b[0] = '\0';

    int z;
    for (z = 128; z > 0; z >>= 1)
    {
        strcat(b, ((x & z) == z) ? "1" : "0");
    }

    return b;
}

int main(void)
{
    {
        /* binary string to int */

        char *tmp;
        char *b = "0101";

        printf("%d\n", strtol(b, &tmp, 2));
    }

    {
        /* byte to binary string */

        printf("%s\n", byte_to_binary(5));
    }

    return 0;
}

Answer 4

Print bits from any type using less code and resources

This approach has as attributes:

• Works with variables and literals.
• Doesn't iterate all bits when not necessary.
• Call printf only when complete a byte (not unnecessarily for all bits).
• Works for any type.
• Works with little and big endianness (uses GCC #defines for checking).
• Uses typeof() that isn't C standard but is largely defined.

#include <stdio.h>
#include <stdint.h>
#include <string.h>

#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
#define for_endian(size) for (int i = 0; i < size; ++i)
#elif __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
#define for_endian(size) for (int i = size - 1; i >= 0; --i)
#else
#error "Endianness not detected"
#endif

#define printb(value)                                   \
({                                                      \
        typeof(value) _v = value;                       \
        __printb((typeof(_v) *) &_v, sizeof(_v));       \
})

void __printb(void *value, size_t size)
{
        uint8_t byte;
        size_t blen = sizeof(byte) * 8;
        uint8_t bits[blen + 1];

        bits[blen] = '\0';
        for_endian(size) {
                byte = ((uint8_t *) value)[i];
                memset(bits, '0', blen);
                for (int j = 0; byte && j < blen; ++j) {
                        if (byte & 0x80)
                                bits[j] = '1';
                        byte <<= 1;
                }
                printf("%s ", bits);
        }
        printf("\n");
}

int main(void)
{
        uint8_t c1 = 0xff, c2 = 0x44;
        uint8_t c3 = c1 + c2;

        printb(c1);
        printb((char) 0xff);
        printb((short) 0xff);
        printb(0xff);
        printb(c2);
        printb(0x44);
        printb(0x4411ff01);
        printb((uint16_t) c3);
        printf("\n");

        return 0;
}

Output

$ ./printb 
11111111 
11111111 
00000000 11111111 
00000000 00000000 00000000 11111111 
01000100 
00000000 00000000 00000000 01000100 
01000100 00010001 11111111 00000001 
00000000 01000011 

---

I have used another approach (bitprint.h) to fill a table with all bytes (as bit strings) and print them based on the input/index byte. It's worth taking a look.

Answer 5

Based on @William Whyte's answer, this is a macro that provides int8,16,32 & 64 versions, reusing the INT8 macro to avoid repetition.

/* --- PRINTF_BYTE_TO_BINARY macro's --- */
#define PRINTF_BINARY_PATTERN_INT8 "%c%c%c%c%c%c%c%c"
#define PRINTF_BYTE_TO_BINARY_INT8(i)    \
    (((i) & 0x80ll) ? '1' : '0'), \
    (((i) & 0x40ll) ? '1' : '0'), \
    (((i) & 0x20ll) ? '1' : '0'), \
    (((i) & 0x10ll) ? '1' : '0'), \
    (((i) & 0x08ll) ? '1' : '0'), \
    (((i) & 0x04ll) ? '1' : '0'), \
    (((i) & 0x02ll) ? '1' : '0'), \
    (((i) & 0x01ll) ? '1' : '0')

#define PRINTF_BINARY_PATTERN_INT16 \
    PRINTF_BINARY_PATTERN_INT8              PRINTF_BINARY_PATTERN_INT8
#define PRINTF_BYTE_TO_BINARY_INT16(i) \
    PRINTF_BYTE_TO_BINARY_INT8((i) >> 8),   PRINTF_BYTE_TO_BINARY_INT8(i)
#define PRINTF_BINARY_PATTERN_INT32 \
    PRINTF_BINARY_PATTERN_INT16             PRINTF_BINARY_PATTERN_INT16
#define PRINTF_BYTE_TO_BINARY_INT32(i) \
    PRINTF_BYTE_TO_BINARY_INT16((i) >> 16), PRINTF_BYTE_TO_BINARY_INT16(i)
#define PRINTF_BINARY_PATTERN_INT64    \
    PRINTF_BINARY_PATTERN_INT32             PRINTF_BINARY_PATTERN_INT32
#define PRINTF_BYTE_TO_BINARY_INT64(i) \
    PRINTF_BYTE_TO_BINARY_INT32((i) >> 32), PRINTF_BYTE_TO_BINARY_INT32(i)
/* --- end macros --- */

#include <stdio.h>
int main() {
    long long int flag = 1648646756487983144ll;
    printf("My Flag "
           PRINTF_BINARY_PATTERN_INT64 "\n",
           PRINTF_BYTE_TO_BINARY_INT64(flag));
    return 0;
}

This outputs:

My Flag 0001011011100001001010110111110101111000100100001111000000101000

For readability you may want to add a separator for eg:

My Flag 00010110,11100001,00101011,01111101,01111000,10010000,11110000,00101000

Answer 6

Print the least significant bit and shift it out on the right. Doing this until the integer becomes zero prints the binary representation without leading zeros but in reversed order. Using recursion, the order can be corrected quite easily.

#include <stdio.h>

void print_binary(int number)
{
    if (number) {
        print_binary(number >> 1);
        putc((number & 1) ? '1' : '0', stdout);
    }
}

To me, this is one of the cleanest solutions to the problem. If you like 0b prefix and a trailing new line character, I suggest wrapping the function.

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