پاورپوینت کامل Real-World File Structures 17 اسلاید در PowerPoint

قسمتی از پاورپوینت :

Data About Data
Usually in the form of a file header
Example in text
Astronomy image storage format
HTML format (name = value)
But look on page 177: coding style makes a BIG difference
Parsing this kind of data
Read field name; read field value
Convert ASCII value to type required for storage & use
Store converted value into right variable
Why use this type of header
Graphics Storage Formats
Data
Color values for each pixel in image
Data compression often used (GIF, JPG)
Different color “depth” possibilities
Metadata
Height & width of image
Number of bits per pixel (color depth)
If not true color (24 bits / pixel)
Color look-up table
Normally 256 entries
Indexed by values stored for each pixel (normally 1 byte)
Contains R/G/B values for color combination
Often formatted to be loaded directly into graphics RAM
Objective
Store different types of data in the same file
Textbook example – mix of astronomy data
Main file header (HTML-style)
Sub-files of notes – lines of ASCII text
Sub-files of image data – in whatever format is needed
So our main file becomes a file of sub-files
Each sub-file (header, notes, or image) is really a “record” in the main file
These “records” are of varying length & format
How do we store the actual records in the sub-file “records”
Could use another level of specified-length record software
Better – do what makes sense in the situation(s)