CODEWITHSUNDEEP
pythonstructpack
Jon
Jon

Reputation: 477

Python struct.pack()/calcsize()

I want to pack a byte followed by a long. My buffer can only contain 9 elements. Why can't I pack them into the buffer?

>>> from struct import *
>>> calcsize('qB')
9
>>> calcsize('Bq')
12

It returns differently. Why is this?

I'm using Python 2.7.3 by the way.

Upvotes: 1

Views: 1883

Answers (1)

chepner
chepner

Reputation: 530872

In your second example, struct.calcsize assumes 3 bytes of padding after the byte so that the long long can begin on a 4-byte boundary.

If you specify no padding, you'll see they are equivalent:

>>> calcsize ('Bq')
12
>>> calcsize('=Bq')
9

Upvotes: 1

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