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Inside Macintosh: Files /
Chapter 1 - Introduction to File Management / File Management Reference
File Access Routines / Manipulating the File Mark


You can use the SetFPos function to set the position of the file mark before reading from or writing to an open file.

FUNCTION SetFPos (refNum: Integer; posMode: Integer; 
                  posOff: LongInt): OSErr;
The file reference number of an open file.
The positioning mode.
The positioning offset.
The SetFPos function sets the file mark of the specified file. The posMode parameter indicates how to position the mark; it must contain one of the following values:

   fsAtMark    = 0;  {at current mark}
   fsFromStart = 1;  {set mark relative to beginning of file}
   fsFromLEOF  = 2;  {set mark relative to logical end-of-file}
   fsFromMark  = 3;  {set mark relative to current mark}
If you specify fsAtMark, the mark is left wherever it's currently positioned, and the posOff parameter is ignored. The next three constants let you position the mark relative to either the beginning of the file, the logical end-of-file, or the current mark. If you specify one of these three constants, you must also pass in posOff a byte offset (either positive or negative) from the specified point. If you specify fsFromLEOF, the value in posOff must be less than or equal to 0.

noErr0No error
ioErr-36I/O error
fnOpnErr-38File not open
eofErr-39Logical end-of-file reached
posErr-40Attempt to position mark before start of file
rfNumErr-51Bad reference number

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© Apple Computer, Inc.
2 JUL 1996