Reading and writing text or binary files

You use PowerScript text file functions to read and write text in line mode or stream mode, or to read and write binary files in stream mode.

The FileOpen function can open Unicode and ANSI files. If the file does not exist, FileOpen creates a Unicode file. The FileClose function saves the file in the format in which it was opened.

• In line mode, the FileRead, FileReadEx, FileWrite, and FileWriteEx functions can read and write to Unicode files.

  You can read a file a line at a time until either a carriage return or line feed (CR/LF) or the end-of-file (EOF) is encountered. When writing to the file after the specified string is written, PowerScript appends a CR/LF.

• In stream mode, the FileRead, FileReadEx, FileWrite, and FileWriteEx functions can read and write to Unicode and ANSI files. FileOpen and the file read and write functions assume that any file is a binary file. FileOpen opens the file as a binary file; FileWrite and FileWriteEx writes to it as a binary file.

  You can read the entire contents of the file, including any CR/LFs. When writing to the file, you must write out the specified string (but not append a CR/LF).

  The format in which FileWrite and FileWriteEx append data to a file depends on the format of the data, not the format of the file. If you append a string entered in PocketBuilder to an ANSI file, it is written as a Unicode character string. If you are reading from or writing to ANSI files in stream mode, use the FromANSI and ToANSI functions to convert ANSI blobs to Unicode character strings, or Unicode characters to ANSI blobs.

  This code opens an ANSI file in stream mode, reads the data into a blob, then converts the blob into a Unicode string:

  long ll_fnum
  integer li_bytes
  string ls_unicode
  blob  lb_ansill_fnum = FileOpen("employee.dat",StreamMode!,
     Read!, LockWrite!, Replace!)li_	bytes = FileRead(ll_fnum, lb_ansi)
  ls_unicode = FromANSI(lb_ansi)
  FileClose(ll_fnum)
  

  This code converts a Unicode character string into an ANSI blob, opens an ANSI file in stream mode, and writes the blob to the file:

  lb_ansi = ToANSI(ls_unicode)
  ll_fnum = FileOpen("employee.dat",StreamMode!,
     Write!, LockWrite!, Replace!)li_	bytes = FileWrite(ll_fnum, lb_ansi)
  FileClose(ll_fnum)
  

  If the file is in Unicode format and has the two-byte flag, use the Mid function to skip the leading bytes when the file is opened in stream mode:

  bytes = fileread(ll_fnum, ls_unicode)
  ls_string = Mid(ls_unicode, 2)
  

Understanding the position pointer

When PocketBuilder opens a file, it assigns the file a unique integer and sets the position pointer for the file to the position you specify (the beginning or end of the file). You use the integer to identify the file when you want to read the file, write to it, or close it. The position pointer defines where the next read or write will begin. PocketBuilder advances the pointer automatically after each read or write.

You can also set the position pointer with the FileSeek function.

File functions

Table 19-3 lists the built-in PowerScript functions that manipulate files.

---

Copyright © 2007. Sybase Inc. All rights reserved.

View this book as PDF