I am writing a bitmap file using python. My code to create the bitmap header is:
pack('bblll', 66, 77, fileLength, 0, 122)
Unless my math is wrong, (Which, it's not) this should create a string of bytes that is 14 bytes long.
b = char (1 byte) l = long (4 bytes)
1 +たす 1 +たす 4 +たす 4 +たす 4 =わ 14
But, the thing is, I receive 2 extra bytes; Say I have a filelength of 142, I would receive the following (in hexidecimal):
42 4D 00 00 8E 00 00 00 00 00 00 00 7A 00 00 00
The 2 extra bits are nulls at offset 0x2 and 0x3. Where do They come from? And How do I get rid of them? It is corrupting my images.
asked Aug 26, 2012 at 23:44
Jacob Valenta
6,8198 gold badges34 silver badges42 bronze badges
1 Answer 1
It pads to four-byte (word) boundaries so the longs start at natural offsets (i.e. offsets that are a multiple of four), use the = prefix (or any other of the possible byte order prefixes) to prevent this.
answered Aug 26, 2012 at 23:47
Alexander Gessler
46.9k7 gold badges87 silver badges124 bronze badges
Sign up to request clarification or add additional context in comments.
1 Comment
Jacob Valenta
You are my hero. I must have looked right over that; A little while ago, I had to use little endian by using a '<', can't believe I missed that.
lang-py