programming-for-dummies

270
Storing Varying Size Data in Untyped Files
Inside the WHILE loop is the BlockRead command, which tells the computer
to read one (1) block of data at a time (when each block of data is
defined in size by the Reset command), as shown in Figure 8-4.
Figure 8-4:
The
computer
can retrieve
data from an
untyped file
in blocks or
chunks.
To retrieve data from an untyped file, the computer
retrieves a fixed chunk of data at a time.
After the BlockRead command retrieves data from the file identified by the
myFile variable, it stores this data in a Storage variable. The ShowMessage
command displays the value of the Storage variable on-screen.
Reading an untyped file from start to finish can be as slow and cumbersome
as reading an entire text file from start to finish. So as a second way to retrieve
data from an untyped file, you can use a pointer to “point” to different data
blocks.
For example, suppose you use the Reset command to define a block of 5
bytes:
Reset(myFile, 5);
This command divides an untyped file into 5-byte blocks.
To access an untyped file, like a random-access file, you can use the Seek
command, which defines which untyped file to use and which data chunk to
retrieve like this:
Seek(myFile, 3);
This command tells the computer to use the untyped file identified by the
myFile variable and retrieve all the data in the third block of data, as shown
in Figure 8-5.
After the computer finishes retrieving data from the file, it needs to close the
file by using the CloseFile command:
CloseFile(myFile);