The default is octal.
Except for types `a' and `c', you can specify the number of bytes to use in interpreting each number in the given data type by following the type indicator character with a decimal integer. Alternately, you can specify the size of one of the C compiler's built-in data types by following the type indicator character with one of the following characters. For integers (d, o, u, x):
For floating point (f):
The next several options map the old, pre-POSIX format specification options to the corresponding POSIX format specs. GNU od accepts any combination of old- and new-style options. Format specification options accumulate.