Converting floating-point number to IEEE754 representation by using union and struct in c.

floating_point_ieee.c

#include <stdio.h>
/*
 * See also : http://class.ece.iastate.edu/arun/CprE281_F05/ieee754/ie5.html
 */

union FloatingPointIEEE754 {
	struct {
		unsigned int mantissa : 23;
		unsigned int exponent : 8;
		unsigned int sign : 1;
	} raw;
	float f;
} number;

int main() {
	number.f = -6.8;
	printf("%x, %x, %x", number.raw.mantissa, number.raw.exponent, number.raw.sign ); 
	return 0;
}

Not pretty, but I came up with this one to properly display the number. @kamalhyder

#include <stdio.h>

#define BYNARY_FMT "%u%u%u%u%u%u%u%u"
#define BYTE_TO_BIN(b) ((b) & 0x80 ? 1 : 0),\
                       ((b) & 0x40 ? 1 : 0),\
                       ((b) & 0x20 ? 1 : 0),\
                       ((b) & 0x10 ? 1 : 0),\
                       ((b) & 0x08 ? 1 : 0),\
                       ((b) & 0x04 ? 1 : 0),\
                       ((b) & 0x02 ? 1 : 0),\
                       ((b) & 0x01 ? 1 : 0)
					   
#define BIT_FMT "%u"
#define NTH_BIT(b, n) ((b) & (1 << n) ? 1 : 0)

union FloatingPointIEEE754 {
	struct {
		unsigned int m: 23;
		unsigned int e: 8;
		unsigned int s: 1;
	} raw;
	float f;
} ieee754;

int main() {
	ieee754.f = -6.8;
		
	printf(
		BIT_FMT " "
		BYNARY_FMT " "
		BIT_FMT BIT_FMT BIT_FMT BIT_FMT BIT_FMT BIT_FMT BIT_FMT BYNARY_FMT BYNARY_FMT "\n\n",
		
		// SIGN
		NTH_BIT    (ieee754.raw.s      , 0),
		
		// EXPONENT
		BYTE_TO_BIN(ieee754.raw.e         ),
		
		// MANTISSA
		NTH_BIT    (ieee754.raw.m >> 16, 6),
		NTH_BIT    (ieee754.raw.m >> 16, 5),
		NTH_BIT    (ieee754.raw.m >> 16, 4),
		NTH_BIT    (ieee754.raw.m >> 16, 3),
		NTH_BIT    (ieee754.raw.m >> 16, 2),
		NTH_BIT    (ieee754.raw.m >> 16, 1),
		NTH_BIT    (ieee754.raw.m >> 16, 0),
		BYTE_TO_BIN(ieee754.raw.m >> 8    ),
		BYTE_TO_BIN(ieee754.raw.m         )
	);
	
	return 0;
}