Thread: Big Endian to Little Endian

I am trying to convert 64 bit vale from Big Endian to Little Endian for a 32 bit processor. Can anybody help me with this?

Yes, we can help you. Where are you stuck? What don't you get? Post your code in code tags. If you don't know where to start, look up some tutorials, like this one: Cprogramming.com FAQ > Bit shifting and bitwise operations.

Now I modified my code to:
unsigned long *final;
double final_pos_lat ;
final = &last; /*copy last 4 bytes of data*/
(*final) += 4;
final = &first; /*copy first 4 bytes of data*/
final_pos_lat = *final;

But final_pos_lat has only the value of first 4 bytes*/

Basically I am trying to copy first and last 4 bytes of data into double (8 byte variable)

Please use code tags when posting code in the future. You've gotten yourself all mixed up with dereferencing and incrementing:

Code:

final = &last;  // this sets final to point to the unsigned long variable 'last'
(*final) += 4;  // this dereferences final (effectively giving you 'last') and adds 4 to it, i.e. it's like last += 4
final = &first;  // set final to point to the unsigned long variable 'first'
final_pos_lat = *final;  // dereference final, giving you 'first', and assign that value to final_pos_lat

You really need to review how to use pointers. Here are a couple tutorials:
Pointers in C - Tutorial - Cprogramming.com
Eternally Confuzzled - All About Pointers

Instead, you can use the array operator to assign the two halves:

Code:

unsigned ong *final;
double final_pos_lat;
final = (unsigned long *) &final_pos_lat;  // set final to the location we want to write to
final[0] = first;  // you may want to switch whether [0] is first or last
final[1] = last;

Ohh Ya i really need to go thru pointers properly.
Thanks so much. You solved my problem