CODEWITHSUNDEEP
carrayspointersendianness
bonkerz11
bonkerz11

Reputation: 13

Trying to utilize little endian and big endian with hex input

I am attempting to write C functions with these two prototypes:

int extract_little (char* str, int ofset, int n);
int extract_big(char* str, int ofset, int n);

Now the general idea is I need to return a n byte integer in both formats starting from address str + ofset. P.S. Ofset doesn't do anything yet, I plan on (trying) to shuffle the memory via an offset once I figure out the little endian, for the big.

I'v trying to get it to output like this; for little endian, based off of i=0xf261a3bf;, 0xbf 0xa3 0x61 0xf2

int main()
{
    int i = 0xf261a3bf;
    int ofset = 1; // This isn't actually doing anything yet
    int z;
    for (z = 0; z < sizeof(i); z++){ 
        printf("%x\n",extract_little((char *)&i,ofset, sizeof(i)));
    }
    return 0;
}

int extract_little(char *str,int offs, int n) {
    int x;
    for (x = 0; x < n; x++){
        return str[x];
    }
}

I'm not sure what else to try. I figured out the hard way that even thought I put it in a for loop I still can't return more than 1 value from the return.

Thanks!

Upvotes: 0

Views: 240

Answers (2)

Peter - Reinstate Monica
Peter - Reinstate Monica

Reputation: 16049

With respect to your code: return does what it says, it returns from the function. The loop is never run for more than the first element.

With respect to the problem: Check out htonl and ntolh, except for exercise.

Upvotes: 1

deviantfan
deviantfan

Reputation: 11434

unsigned long extract_little(const void *p, size_t offset, unsigned char n) {
    unsigned long ret = 0;
    for(size_t i = offset + n - 1; i >= offset; i--)
        ret = (ret<<8) + ((char *)p)[i];
    return ret;
}
unsigned long extract_big(const void *p, size_t offset, unsigned char n) {
    unsigned long ret = 0;
    for(size_t i = offset; i < (offset + n); i++)
        ret = (ret<<8) + ((char *)p)[i];
    return ret;
}

int main()
{
    int i = 0xf261a3bf;
    printf("%x\n", extract_little(&i, 0, sizeof(i)));
    return 0;
}

Works (of course) only with n´s which are sizeof(unigned long) maximal.
And can be speed-improved, probably (depending on the compiler optimization).

Upvotes: 1

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