C++ :: Converting Integer To Vector And Back

I'm able to convert an integer to a vector<unsigned char> and back. However, when I try to use a nearly identical function designed for the long long data type, the last byte or two is broken.

Program code:

long long num = 9223372036854775551LL;
cout << "Before: " << num << endl;
vector<unsigned char> data = getBytes(num);
num = getLongLong(data);
cout << "After: " << num << endl;

Code for converting between vector<unsigned char> and long long:

Code:
vector<unsigned char> getBytes(long long value) {
int bytes = sizeof(value);
vector<unsigned char> data(bytes);
for (int i = 0; i < bytes; i++)
data.at(i) = (unsigned char)( value >> ((bytes-i)*8) );

[Code] ....

Output:

Code:
Before: 9223372036854775807
After: 9223372036854775552

Is there something special about long long that would prevent this from working? This problem doesn't happen with int.