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Saving and Retrieving Data
in a Binary File
Text files can be convenient for storing long strings of information, but they can be painfully cumbersome in retrieving data. Random-access files make retrieving data simple but at the expense of having to organize every chunk of data into records. In case you want to store long bits of information with the convenience of retrieving them quickly, you can save data in a binary file.
Creating a new binary file
Before you can store any data in a binary file, you must first create that binary file. To create a binary file, you use the following Liberty BASIC command:
OPEN “Filename” FOR BINARY AS #Handle
This is what the above Liberty BASIC command tells the computer:
1.The OPEN command tells the computer, “Create a new file and give it the name that “Filename” specifies, which can represent a filename (such as STUFF.BIN) or a drive, directory, and filename (such as C:\WINDOWS\ STUFF.BIN).”
2.The FOR BINARY portion of the command tells the computer, “Get ready to start outputting data into the newly created binary file that “Filename” identifies.”
3.The #Handle is any nickname that you choose to represent the binary file you just created.
If you want to create a file called STUFF.BIN and save it on a floppy disk (the A drive), use the following command:
OPEN “A:\STUFF.BIN” FOR BINARY AS #Secrets
This line tells Liberty BASIC to create the binary file STUFF.BIN on the A drive and assign it the name #Secrets.
Any time that you use the OPEN command to create a new binary file or to open an existing binary file, make sure you use the CLOSE command to shut the binary file. If you don’t use the CLOSE command eventually, your program may cause the computer to crash.
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Saving stuff in a binary file
After you create a binary file, you can stuff it with data by using the PRINT command. If you use the PRINT command, Liberty BASIC normally displays that data on-screen, so you must tell Liberty BASIC to store the data in your binary file instead by using the handle of that binary file, as in the following command:
PRINT #Secrets, “This line gets stored in the binary file.”
This command tells Liberty BASIC, “Look for a binary file that the name #Secrets identifies and stuff that binary file with the line, This line gets stored in the binary file.”
Putting it all together, you can create a program similar to the following example:
OPEN “A:\STUFF.BIN” FOR BINARY AS #Secrets
PRINT #Secrets, “This line gets stored in the binary file.”
CLOSE #Secrets
END
This Liberty BASIC program tells the computer to do the following:
1.The first line tells the computer, “Open a binary file on the A drive and call this binary file STUFF.BIN. Then give it the handle #Secrets.”
2.The second line tells the computer, “Look for a file that the #Secrets handle identifies and stuff it with the line, This line gets stored in the binary file.”
3.The third line tells the computer, “Close the binary file that the #Secrets handle identifies.”
4.The fourth line tells the computer that the program is at an end.
If you run this program, it simply creates a binary file on your disk but you won’t see anything on the screen.
Changing stuff in a binary file
When you store data in a binary file, you can overwrite that data at any time by using something magical called a file pointer. Because binary files store data as a continuous stream of bytes, the file pointer lets you point at the part of the file that contains the data you want to overwrite.
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To find the current location of the file pointer, you have to create a variable and assign it the value of the file pointer’s position with the LOC command such as:
FilePointer = LOC(#Filename)
So if #Filename represents a binary file that contains the string, “I love programming with Liberty BASIC,” the value of the FilePointer variable initially would be 38 (the total number of characters in the “I love programming with Liberty BASIC” string).
To move the file pointer, you have to use the SEEK command, such as:
SEEK(#Filename), NewPosition
This command tells Liberty BASIC, “Move the file pointer to the location specified by NewPosition.” So if the value of NewPosition is 3, the file pointer will now point to the third character stored in the binary file. If you stored the string “I hate copycat publishers,” in a binary file, the third position would point to the letter h, which is the first letter of the word “hate”.
To overwrite data in a binary file, you just have to move the file pointer to the location where you want to overwrite the data and then use the ordinary PRINT command such as:
SEEK(#MyStuff), 3
PRINT #MyStuff, “despise copycat publishers.”
If the #MyStuff handle represented a binary file that contained the string, “I hate copycat publishers,” then the above two commands would first move the file pointer to the third position and then overwrite the third position and the rest of the file with the string “despise copycat publishers.”
Be careful when overwriting data in a binary file. Say you have the following string stored in a binary file, “I like cats,” and use the following code:
SEEK(#MyStuff), 1
PRINT #MyStuff, “‘m tired.”
This is what your original binary file contains:
I like cats.
And this is what the overwritten binary file contents now look like:
I’m tired.s.
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Note that the extra s and period remain because the new string doesn’t completely overwrite the old data in the binary file.
Retrieving stuff from a binary file
Storing data in a binary file is nice, but eventually you may want to retrieve that data out again. To retrieve data from a binary file, you have to move the file pointer to anywhere in the file where you want to start retrieving data, then use the INPUT command such as:
SEEK #MyFile, 0
INPUT #MyFile, RetrieveMe$
In this example, the SEEK #MyFile, 0 command simply moves the file pointer to the beginning of the binary file. If you only wanted to retrieve part of the data in a binary file, you could move the file pointer to a different location such as 8 or 12. #MyFile represents the file handle that you previously used with the OPEN command and RetrieveMe$ is the name of a string variable that temporarily stores the string you stored in that binary file.
If you’re retrieving numeric data stored in a binary file, you would use a numeric variable name that doesn’t have the dollar sign ($) after it, such as:
INPUT #MyFile, RetrieveMe
To see how to store, overwrite and retrieve data in a binary file, take a look at this example:
OPEN “STUFF.BIN” FOR BINARY AS #myfile
PRINT #myfile, “Welcome back home!”
SEEK #myfile, 0
INPUT #myfile, txt$
PRINT “Current Data in binary file: “; txt$
SEEK #myfile, 8
PRINT #myfile, “to my world!”
SEEK #myfile, 0
INPUT #myfile, txt$
PRINT “New Data in binary file: “;txt$
CLOSE #myfile
END
Here’s what’s happening in the preceding example:
1.The first line tells the computer, “Open up the binary file STUFF.BIN, assign it a file handle of #myfile.”
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2.The second line tells the computer to store the string, “Welcome back home!” in the binary file.
3.The third line tells the computer to move the file pointer to the beginning of the binary file.
4.The fourth line tells the computer, “Read all the data out of the binary file represented by the #myfile handle and store the result in a variable called txt$.”
5.The fifth line tells the computer, “Print the current contents of the binary file in the main window, which means Liberty BASIC prints the string, “Welcome back home!””
6.The sixth line tells the computer, “Move the file pointer to the eight position in the binary file.”
7.The seventh line tells the computer, “Starting with the eighth position in the binary file, overwrite the data and replace it with the string, “to my world!””
8.The eighth line tells the computer, “Move the file pointer back to the front of the binary file.”
9.The ninth line tells the computer, “Read all the data from the binary file represented by the handle #myfile, and store it in a variable called txt$.”
10.The tenth line tells the computer, “Print the contents of the binary file in the main window.”
11.The eleventh line tells the computer, “Close the binary file represented by the #myfile handle.”
12.The twelfth line tells the computer, “This is the end of the program. Now it’s safe for Microsoft Windows to crash without losing any of my valuable data.”