A sequential text file is a file where characters are placed in sequence, one right after the other. Sequential text files have no set format other than a beginning and an end. A sequential text file can only be read starting from the beginning of the file. Each character is printed as an ASCII text character. The most common example of a sequential text file is the .txt file saved with Notepad or any other editing tool. Run the following code to see the output of simple PRINT statements.
PRINT "Tom Sawyer"
PRINT "Huckleberry Finn"
PRINT "The Prince and the Pauper"
PRINT "A Connecticut Yankee in King Arthur's Court"
PRINT "A Tramp Abroad"
Output
Tom Sawyer
Huckleberry Finn
The Prince and the Pauper
A Connecticut Yankee in King Arthur's Court
A Tramp Abroad
When the program is closed, the text is gone. A sequential text file allows that text to be saved to file.
Sequential File Commands and Operations
There are three basic operations in sequential text files.
Creating and writing data into a file
Reading data from an existing file
Appending or adding data into an existing file
Basic File commands and functions include
OPEN- used to access the file
OUTPUT - used to write data to the file
INPUT - used to read data from the file
LOF() - length of file
EOF() - end of file
CLOSE - used to close the file
Special File commands and functions include
LINE INPUT - extract a full line of data
INPUTTO$ - extract data up to the assigned deliminator
INPUT$() - extract a number of bytes of data starting from the beginning
Creating a Sequential Text File
Sequential text files are always created in this fashion
OPEN "FileName.ext"for OUTPUT as #1
The commands OPEN and OUTPUT are case-insensitive. "FileName.ext" can be any name and extension you choose. The file name can also be a variable.
fName$ ="FileName.ext"
OPEN fName$ for OUTPUT as #1
#1 is also an arbitrary name. #a, #MyTextFile, #123xyz, or any other combination of numbers and letters will work as well.
Once the file has been opened, data can be written into that file. The data can be literal
PRINT #1, "Tom Sawyer"
or a variable
t$ ="Tom Sawyer"
PRINT #1, t$
Finally, when all the data has been written, the file must be closed.
CLOSE #1
The following code creates the text file "TwainNovels.txt"
OPEN "TwainNovels.txt"for OUTPUT as #1
PRINT #1, "Tom Sawyer"
PRINT #1, "Huckleberry Finn"
PRINT #1, "The Prince and the Pauper"
PRINT #1, "A Connecticut Yankee in King Arthur's Court"
PRINT #1, "A Tramp Abroad"
CLOSE #1END
Run the above code before proceeding with this tutorial.
Reading a Sequential Text File
Reading a sequential text file also requires the file be OPENed, but for INPUT.
OPEN "TwainNovels.txt"for INPUT as #1
INPUT #1, n1$
INPUT #1, n2$
INPUT #1, n3$
INPUT #1, n4$
INPUT #1, n5$
CLOSE #1
PRINT n1$
PRINT n2$
PRINT n3$
PRINT n4$
PRINT n5$
END
Output
Tom Sawyer
Huckleberry Finn
The Prince and the Pauper
A Connecticut Yankee in King Arthur's Court
A Tramp Abroad
LOF - Length of File
The length, or size, of a sequential text file is determined by the number of characters it contains. Each character occupies one byte. That size is obtained with the LOF() function. The file must first be opened.
LOF = 118
Tom Sawyer
Huckleberry Finn
The Prince and the Pauper
A Connecticut Yankee in King Arthur's Court
A Tramp Abroad
nChars = 108
There is an inequality here. LOF equals 118 and nChars equals 108. Where are the other 10 characters?
End-of-Line Markers
Windows marks the end of each record with a carriage return / line feed sequence. At the end of each novel title are these two end-of-line marker characters: Chr$(13) and Chr$(10), two extra characters for each of the five lines. That's ten extra characters.
Sequential text files save all characters in their corresponding ASCII format and display as they do on the keyboard. The letter 'a' is seen as 'a', the number 1 is seen as '1'. Some characters, Control Key, Escape, Enter, to name a few, are invisible characters. They are imbedded in the sequential text file but cannot be seen. The LOF() function incudes these characters when counting the size of the file. The INPUTed variables do not include these end-of-line markers.
EOF - End of File
Liberty BASIC uses a special End of File function, EOF(), to determine if the End of File has been reached. If the End of File has been reached, EOF returns 1 (True). If the End of File has not been reached, EOF returns 0 (False). EOF is useful for retrieving information when the file contains an unknown amount of data.
OPEN "TwainNovels.txt"for INPUT as #1WHILEEOF(#1)=0
INPUT #1, n$
PRINT n$
WEND
CLOSE #1END
Output
Tom Sawyer
Huckleberry Finn
The Prince and the Pauper
A Connecticut Yankee in King Arthur's Court
A Tramp Abroad
WHILE EOF(#1) = 0 translates to While the End of File is false (hasn't been reached)
This could also be coded as
OPEN "TwainNovels.txt"for INPUT as #1WHILEEOF(#1)<>1
INPUT #1, n$
PRINT n$
WEND
CLOSE #1END
Output
Tom Sawyer
Huckleberry Finn
The Prince and the Pauper
A Connecticut Yankee in King Arthur's Court
A Tramp Abroad
WHILE EOF(#1) <> 1 translates to While the End of File is not true (hasn't been reached)
In either case, the code continues to input data until the End of File has been reached.
Counting the Data
Sometimes the number of data needs to be known. This is especially true if an array is used to capture the data. If a sequential text file contains an unknown number of data, use a counter to determine that exact number. Increase the counter by one with each data read.
ct =0
OPEN "TwainNovels.txt"for INPUT as #1DO
ct = ct +1
INPUT #1, n$
PRINT ct, n$
LOOPWHILEEOF(#1)=0
CLOSE #1
PRINT "There are ";ct;" items of data in this text file."END
Output
1 Tom Sawyer
2 Huckleberry Finn
3 The Prince and the Pauper
4 A Connecticut Yankee in King Arthur's Court
5 A Tramp Abroad
There are 5 items of data in this text file.
Once the number of data is known, DIM the array, OPEN the file again, and INPUT the data into the array. Be sure to CLOSE the file first so the INPUT begans with the first data.
nNovels =5' The number obtained by the counterDim TwainNovel$(nNovels)
OPEN "TwainNovels.txt"for INPUT as #1FOR i =1to nNovels
INPUT #1, TwainNovel$(i)NEXT i
CLOSE #1FOR i =1to nNovels
PRINT TwainNovel$(i)NEXT i
END
Output
Tom Sawyer
Huckleberry Finn
The Prince and the Pauper
A Connecticut Yankee in King Arthur's Court
A Tramp Abroad
Recapping
To read a known number of data from a sequential file
OPEN the file
use a FOR NEXT loop to INPUT data
CLOSE the file
To read an unknown number of data from a sequential text file
OPEN the file
use a WHILE WEND to INPUT data until the EOF is reached
CLOSE the file
To count the number of data in a sequential text file
OPEN the file
use a counter
use a DO LOOP to INPUT data until EOF is reached
CLOSE the file
OPEN the file again
use a FOR NEXT loop to INPUT data
CLOSE the file again
Comma Deliminators
It's not just End of Line markers that separate data; a comma will also separate data. Deliminator is another word for separator. Run this code to create a new file.
OPEN "SevenDwarves.txt"for OUTPUT as #1
PRINT #1, "Happy, Sleepy, Bashful, Grumpy, Sneezey, Doc, Dopey"
CLOSE #1END
Next, read the file.
OPEN "SevenDwarves.txt"for INPUT as #1
INPUT #1, dwarf$
PRINT dwarf$
CLOSE #1END
Output
Happy
Where are the rest of the dwarves? INPUT will only grab data up to, but not including, the comma. Use either a FOR NEXT loop if you know the number of data to INPUT
' Number of data is known
OPEN "SevenDwarves.txt"for INPUT as #1FOR i =1to7
INPUT #1, dwarf$
PRINT dwarf$
NEXT i
CLOSE #1END
Output
Happy
Sleepy
Bashful
Grumpy
Sneezey
Doc
Dopey
or use a WHILE WEND loop if you don't.
' Number of data unknown
OPEN "SevenDwarves.txt"for INPUT as #1WHILEEOF(#1)=0
INPUT #1, dwarf$
PRINT dwarf$
WEND
CLOSE #1END
Output
Happy
Sleepy
Bashful
Grumpy
Sneezey
Doc
Dopey
It isn't always desirable to deliminate data with commas. To place the entire line of data, including any commas, in a variable, use LINE INPUT.
Line Input
LINE INPUT will extract the full line of data, up to the End of Line markers. LINE INPUT ignores commas as deliminators.
OPEN "SevenDwarves.txt"for INPUT as #1
LINE INPUT #1, dwarf$
PRINT dwarf$
CLOSE #1END
Actually, any character can be assigned as the deliminator. The assigned deliminator is substituted for the usual comma deliminator. The command for assigning a unique deliminator is INPUTTO$(). The following code separates the SevenDwarves data at the r.
OPEN "SevenDwarves.txt"for INPUT as #1For i =1to2
n$ = INPUTTO$(#1, "r")
PRINT n$
Next i
CLOSE #1END
Output
Happy, Sleepy, Bashful, G
umpy, Sneezey, Doc, Dopey
The unique deliminator, in this case the r, is lost, just as the comma is lost with INPUT. Note, also, that assigning a unique deliminator does not prevent the usual End of Line marker, Chr$(13);Chr$(10), from forcing a new line.
OPEN "TwainNovels.txt"for INPUT as #1WHILEEOF(#1)=0
n$ = INPUTTO$(#1, "r")
PRINT n$
WEND
CLOSE #1END
Output
Tom Sawye
Hucklebe
y Finn
The P
ince and the Paupe
A Connecticut Yankee in King A
thu
's Cou
t
A T
amp Ab
oad
The blank lines are the result of the Chr$(13);Chr$(10) End of Line markers.
Placing the Entire Contents of the File into One String Variable
Partial or full contents of the file can be read using the INPUT$() function. Contents of the file, from the beginning to a defined number of bytes can be placed in a string variable.
OPEN "TwainNovels.txt"for INPUT as #1
n$ =INPUT$(#1, 15)
CLOSE #1
PRINT n$
END
Output
Tom Sawyer
Huc
Only 12 characters are visible. The other 2 bytes are the invisible characters, Chr$(13) and Chr$(10), that force a new line at the end of Tom Sawyer.
OPEN "TwainNovels.txt"for INPUT as #1
n$ =INPUT$(#1, 15)
CLOSE #1
PRINT n$
FOR i =1to LEN(n$)
PRINT i, MID$(n$, i, 1), ASC(MID$(n$, i, 1))NEXT i
END
Output
Tom Sawyer
Huc
1 T 84
2 o 111
3 m 109
4 32
5 S 83
6 a 97
7 w 119
8 y 121
9 e 101
10 r 114
11 13
12 10
13 H 72
14 u 117
15 c 99
The entire contents of the file may be read and stored in one string variable. This may be useful for text files containing narrative paragraphs, or for later parsing of unknown data. Whatever the reason, the entire contents is defined with the LOF() function.
OPEN "TwainNovels.txt"for INPUT as #1
n$ =INPUT$(#1, LOF(#1))
CLOSE #1
PRINT n$
END
Output
Tom Sawyer
Huckleberry Finn
The Prince and the Pauper
A Connecticut Yankee in King Arthur's Court
A Tramp Abroad
Recapping
Read a simple sequential text file with the INPUT command
Read an entire line of data, including commas, with the LINE INPUT command
Read the entire file as one string variable with the INPUT$() and LOF() functions
Appending a Sequential Text File
PRINTing to a sequential text file that's been OPENed for OUTPUT will not place the new text at the end of the file. It will, in fact, overwrite the file.
OPEN "TwainNovels.txt"for OUTPUT as #1
PRINT "The Guilded Age"
CLOSE #1
OPEN "TwainNovels.txt"for INPUT as #1
n$ =INPUT$(#1, LOF(#1))
CLOSE #1
PRINT n$
END
Ouput
The Guilded Age
"The Guilded Age" was not added to the contents of TwainNovels.txt, but, instead, replaced the contents of TwainNovels.txt. To add information to an existing sequential text file, use the APPEND command. First, rebuild the original TwainNovels.txt file.
OPEN "TwainNovels.txt"for OUTPUT as #1
PRINT #1, "Tom Sawyer"
PRINT #1, "Huckleberry Finn"
PRINT #1, "The Prince and the Pauper"
PRINT #1, "A Connecticut Yankee in King Arthur's Court"
PRINT #1, "A Tramp Abroad"
CLOSE #1
Read the contents of the file.
OPEN "TwainNovels.txt"for INPUT as #1FOR i =1to5
INPUT #1, n$
PRINT n$
NEXT i
CLOSE #1END
Output
Tom Sawyer
Huckleberry Finn
The Prince and the Pauper
A Connecticut Yankee in King Arthur's Court
A Tramp Abroad
Now, OPEN the file for APPEND to add more content.
OPEN "TwainNovels.txt"for APPEND as #1
PRINT #1, "The Guilded Age"
CLOSE #1
OPEN "TwainNovels.txt"for INPUT as #1FOR i =1to6
INPUT #1, n$
PRINT n$
NEXT i
CLOSE #1END
Output
Tom Sawyer
Huckleberry Finn
The Prince and the Pauper
A Connecticut Yankee in King Arthur's Court
A Tramp Abroad
The Guilded Age
Recapping
To create a new sequential text file, use OPEN for OUTPUT
To read a sequential text file, use OPEN for INPUT
To add content to an existing text file, use OPEN for APPEND
Advantages and Disadvantages of a Sequential Text File
Sequential text files can be used to store any type of data. The structure is simple and the contents are easily obtainable. Sequential text files must be read starting from the beginning. As files increase in size, it may become time consuming to search for information toward the end of the file. Any change to the file necessitates a rewriting of the entire file to disk. Still, for small amounts of data, sequential text files offer the most economical option.
JanetTerra
Feb 12, 2009
Writing, Reading, and Appending Sequential Text Files
Sequential File Commands and Operations
Creating a Sequential Text File
Reading a Sequential Text File
Appending a Sequential Text File
A sequential text file is a file where characters are placed in sequence, one right after the other. Sequential text files have no set format other than a beginning and an end. A sequential text file can only be read starting from the beginning of the file. Each character is printed as an ASCII text character. The most common example of a sequential text file is the .txt file saved with Notepad or any other editing tool. Run the following code to see the output of simple PRINT statements.
Output
When the program is closed, the text is gone. A sequential text file allows that text to be saved to file.
Sequential File Commands and Operations
There are three basic operations in sequential text files.
Basic File commands and functions include
Special File commands and functions include
Creating a Sequential Text File
Sequential text files are always created in this fashion
The commands OPEN and OUTPUT are case-insensitive. "FileName.ext" can be any name and extension you choose. The file name can also be a variable.
#1 is also an arbitrary name. #a, #MyTextFile, #123xyz, or any other combination of numbers and letters will work as well.
Once the file has been opened, data can be written into that file. The data can be literal
or a variable
Finally, when all the data has been written, the file must be closed.
CLOSE #1The following code creates the text file "TwainNovels.txt"Run the above code before proceeding with this tutorial.
Reading a Sequential Text File
Reading a sequential text file also requires the file be OPENed, but for INPUT.
Output
LOF - Length of File
The length, or size, of a sequential text file is determined by the number of characters it contains. Each character occupies one byte. That size is obtained with the LOF() function. The file must first be opened.
Output
There is an inequality here. LOF equals 118 and nChars equals 108. Where are the other 10 characters?
End-of-Line Markers
Windows marks the end of each record with a carriage return / line feed sequence. At the end of each novel title are these two end-of-line marker characters: Chr$(13) and Chr$(10), two extra characters for each of the five lines. That's ten extra characters.
Sequential text files save all characters in their corresponding ASCII format and display as they do on the keyboard. The letter 'a' is seen as 'a', the number 1 is seen as '1'. Some characters, Control Key, Escape, Enter, to name a few, are invisible characters. They are imbedded in the sequential text file but cannot be seen. The LOF() function incudes these characters when counting the size of the file. The INPUTed variables do not include these end-of-line markers.
EOF - End of File
Liberty BASIC uses a special End of File function, EOF(), to determine if the End of File has been reached. If the End of File has been reached, EOF returns 1 (True). If the End of File has not been reached, EOF returns 0 (False). EOF is useful for retrieving information when the file contains an unknown amount of data.
Output
WHILE EOF(#1) = 0 translates to While the End of File is false (hasn't been reached)
This could also be coded as
Output
WHILE EOF(#1) <> 1 translates to While the End of File is not true (hasn't been reached)
In either case, the code continues to input data until the End of File has been reached.
Counting the Data
Sometimes the number of data needs to be known. This is especially true if an array is used to capture the data. If a sequential text file contains an unknown number of data, use a counter to determine that exact number. Increase the counter by one with each data read.
Output
Once the number of data is known, DIM the array, OPEN the file again, and INPUT the data into the array. Be sure to CLOSE the file first so the INPUT begans with the first data.
Output
Recapping
To read a known number of data from a sequential file
To read an unknown number of data from a sequential text file
To count the number of data in a sequential text file
Comma Deliminators
It's not just End of Line markers that separate data; a comma will also separate data. Deliminator is another word for separator. Run this code to create a new file.
Next, read the file.
Output
Where are the rest of the dwarves? INPUT will only grab data up to, but not including, the comma. Use either a FOR NEXT loop if you know the number of data to INPUT
Output
or use a WHILE WEND loop if you don't.
Output
It isn't always desirable to deliminate data with commas. To place the entire line of data, including any commas, in a variable, use LINE INPUT.
Line Input
LINE INPUT will extract the full line of data, up to the End of Line markers. LINE INPUT ignores commas as deliminators.
Output
Assigning a Unique Deliminator
Actually, any character can be assigned as the deliminator. The assigned deliminator is substituted for the usual comma deliminator. The command for assigning a unique deliminator is INPUTTO$(). The following code separates the SevenDwarves data at the r.
Output
The unique deliminator, in this case the r, is lost, just as the comma is lost with INPUT. Note, also, that assigning a unique deliminator does not prevent the usual End of Line marker, Chr$(13);Chr$(10), from forcing a new line.
Output
The blank lines are the result of the Chr$(13);Chr$(10) End of Line markers.
Placing the Entire Contents of the File into One String Variable
Partial or full contents of the file can be read using the INPUT$() function. Contents of the file, from the beginning to a defined number of bytes can be placed in a string variable.
Output
Only 12 characters are visible. The other 2 bytes are the invisible characters, Chr$(13) and Chr$(10), that force a new line at the end of Tom Sawyer.
Output
The entire contents of the file may be read and stored in one string variable. This may be useful for text files containing narrative paragraphs, or for later parsing of unknown data. Whatever the reason, the entire contents is defined with the LOF() function.
Output
Recapping
Appending a Sequential Text File
PRINTing to a sequential text file that's been OPENed for OUTPUT will not place the new text at the end of the file. It will, in fact, overwrite the file.
Ouput
"The Guilded Age" was not added to the contents of TwainNovels.txt, but, instead, replaced the contents of TwainNovels.txt. To add information to an existing sequential text file, use the APPEND command. First, rebuild the original TwainNovels.txt file.
Read the contents of the file.
Output
Now, OPEN the file for APPEND to add more content.
Output
Recapping
Advantages and Disadvantages of a Sequential Text File
Sequential text files can be used to store any type of data. The structure is simple and the contents are easily obtainable. Sequential text files must be read starting from the beginning. As files increase in size, it may become time consuming to search for information toward the end of the file. Any change to the file necessitates a rewriting of the entire file to disk. Still, for small amounts of data, sequential text files offer the most economical option.
More on Files
An Introduction to Working with Files