Text files

Open, then read or write

• AS topic 10.3 asks for pseudocode that handles a text file of one or more lines.
• Open the file in one mode: READ, WRITE or APPEND.
• WRITE starts a new file and loses what was there. APPEND adds after what is there.
• CLOSEFILE when you have finished. A file is open in only one mode at a time.

OPENFILE "Note.txt" FOR WRITE
WRITEFILE "Note.txt", "Hello"
CLOSEFILE "Note.txt"
DECLARE LineOfText : STRING
OPENFILE "Note.txt" FOR READ
READFILE "Note.txt", LineOfText
CLOSEFILE "Note.txt"
OUTPUT LineOfText

EOF tells you when to stop

• EOF("Note.txt") is TRUE when there is no further line to read.
• WHILE NOT EOF(...) reads every line. READFILE puts the next line into a STRING.

OPENFILE "List.txt" FOR WRITE
WRITEFILE "List.txt", "a"
WRITEFILE "List.txt", "b"
CLOSEFILE "List.txt"
DECLARE LineOfText : STRING
OPENFILE "List.txt" FOR READ
WHILE NOT EOF("List.txt")
  READFILE "List.txt", LineOfText
  OUTPUT LineOfText
ENDWHILE
CLOSEFILE "List.txt"

Watch out

• Declare the string before READFILE uses it.
• Random files (OPENFILE … FOR RANDOM) are A2. This lesson does not use them.

Common mistakes

• Read with READFILE only after OPENFILE … FOR READ.
• WRITE replaces the file. Use APPEND to keep the old lines.

Now you try

• Write two lines, then read them back until EOF.