c programming

Question

int main() {
    int i,n;
    int x = 123456789;
    void *a = &x;
    unsigned char *c1 = (unsigned char*)a;
    for(i=0;i< sizeof a;i++) {
        printf("%u  ",*(c1+i));
    }
    char *c2 = (char*)a;
    printf("\n %d", *(c2+1));
    char *c3 = (char*)a;
    printf("\n %u \n", *(c3+1));
}

Output ?

Answer 1

 int x = 123456789;

See how data will be stored ,

00010101

11001101

01011011

00000111

a is pointing to address of int x.

unsigned char *c1 = (unsigned char*)a;

Now char c1 is pointing to the location of a.

Next statement is printing consequtive 4 bytes which are unsigned in nature.

So value will be:21   205   91    7 (See from above table)

 char *c2 = (char*)a;

Char c2 contains address of a which is signed .Now it is printing second byte value at pointed by a.

And correspoinding value will be -51(which will fall inside signed range ).

 char *c3 = (char*)a;

Char c3 contains address of a which is also signed .Now it is also printing second byte value pointed by a. But it is signed .

PS: *(c3+1) is promoted inside printf to a 32 bit integer , preserving sign. ( padding ones because, initialy *c3 was a signed char having 1 in the sign bit, and it is itself in 2's complement form). After that we read using %u specifier which simply tells how to interpret the promoted data. %u nothing to do with promotion.
So, in the last printf %u reads the promoted data 11111111111111111111111111001101 as 4294967245.

Out:4294967245

Comments

Thanks !!. I would like to add: *(c3+1) is promoted inside printf to a 32 bit integer , preserving sign. ( padding ones because, initialy *c3 was a signed char having 1 in the sign bit, and it is itself in 2's complement form). After that we read using %u specifier which simply tells how to interpret the promoted data. %u nothing to do with promotion. So, in the last printf %u reads the promoted data 11111111111111111111111111001101 as 4294967245.

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thank you

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@Manoj how data are storing ? I am not getting

int is 4 B rt?

then 1=0001

and 2=0010 rt?

how r u getting 0101?

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$(123456789)_{10} = 00000111 \ \ 01011011 \ \ 11001101 \ \ 00010101$
They stored as in little endian system. Lower byte in lower address.

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ok got it :)