How to print out the memory contents of a variable in C?

Question

Suppose I do a

double d = 234.5;

I want to see the memory contents of d [the whole 8 bytes]

How do I do that?

Answer 1

If you want to print the double values in bits try this. I have tried for float value. If you changed that you can be able to view the double value in 64 bits.

#include <stdio.h>

int main (void)
{
        float f = 10.0f;

        struct Float {
                unsigned char bit01:1;
                unsigned char bit02:1;
                unsigned char bit03:1;
                unsigned char bit04:1;
                unsigned char bit05:1;
                unsigned char bit06:1;
                unsigned char bit07:1;
                unsigned char bit08:1;
                unsigned char bit09:1;
                unsigned char bit10:1;
                unsigned char bit11:1;
                unsigned char bit12:1;
                unsigned char bit13:1;
                unsigned char bit14:1;
                unsigned char bit15:1;
                unsigned char bit16:1;
                unsigned char bit17:1;
                unsigned char bit18:1;
                unsigned char bit19:1;
                unsigned char bit20:1;
                unsigned char bit21:1;
                unsigned char bit22:1;
                unsigned char bit23:1;
                unsigned char bit24:1;
                unsigned char bit25:1;
                unsigned char bit26:1;
                unsigned char bit27:1;
                unsigned char bit28:1;
                unsigned char bit29:1;
                unsigned char bit30:1;
                unsigned char bit31:1;
                unsigned char bit32:1;
        };

        struct Float *F;

        F = (struct Float *) &f;

        printf("\nMSB -->1 bit for sign bit; 8 bit for exponent; 23 bit for mantisa<-- LSB\n");
        printf("%d ", F->bit32);
        printf("%d", F->bit31);
        printf("%d", F->bit30);
        printf("%d", F->bit29);
        printf("%d", F->bit28);
        printf("%d", F->bit27);
        printf("%d", F->bit26);
        printf("%d", F->bit25);
        printf("%d ", F->bit24);
        printf("%d", F->bit23);
        printf("%d", F->bit22);
        printf("%d", F->bit21);
        printf("%d", F->bit20);
        printf("%d", F->bit19);
        printf("%d", F->bit18);
        printf("%d", F->bit17);
        printf("%d", F->bit16);
        printf("%d", F->bit15);
        printf("%d", F->bit14);
        printf("%d", F->bit13);
        printf("%d", F->bit12);
        printf("%d", F->bit11);
        printf("%d", F->bit10);
        printf("%d", F->bit09);
        printf("%d", F->bit08);
        printf("%d", F->bit07);
        printf("%d", F->bit06);
        printf("%d", F->bit05);
        printf("%d", F->bit04);
        printf("%d", F->bit03);
        printf("%d", F->bit02);
        printf("%d\n", F->bit01);
}

Answer 2

double d = 234.5;

/* 1. use a union */
union u {
    double d;
    unsigned char c[sizeof(double)];
};
union u tmp;
size_t i;
tmp.d = d;
for (i=0; i < sizeof(double); ++i)
    printf("%02x\n", tmp.c[i]);

/* 2. memcpy */
unsigned char data[sizeof d];
size_t i;
memcpy(data, &d, sizeof d);
for (i=0; i < sizeof d; ++i)
    printf("%02x\n", data[i]);

/* 3. Use a pointer to an unsigned char to examine the bytes */
unsigned char *p = (unsigned char *)&d;
size_t i;
for (i=0; i < sizeof d; ++i)
    printf("%02x\n", p[i]);

All the methods show you the bytes—but the same double value may print the bytes differently on different systems, e.g., due to different encodings (rare), or different endianness.

Answer 3

Did you try taking the address of d and print sizeof( d ) bytes starting from that address?