FSeek()

FSEEK()

Positions the file pointer in a file opened with low-level access

Syntax

      FSEEK( <nHandle>, <nOffset>, [<nOrigin>] ) --> nPosition

Arguments

<nHandle> DOS file handle.

<nOffset> The number of bytes to move.

<nOrigin> The relative position in the file.

Returns

<nPosition> the current position relative to begin-of-file

Description

This function sets the file pointer in the file whose DOS file handle is <nHandle> and moves the file pointer by <expN2> bytes from the file position designated by <nOrigin>. The returned value is the relative position of the file pointer to the beginning-of-file marker once the operation has been completed.

<nHandle> is the file handle number. It is obtained from the FOPEN() or FCREATE() function.

The value of <nOffSet> is the number of bytes to move the file pointer from the position determined by <nOrigin>. The value of <nOffset> may be a negative number, suggesting backward movement.

The value of <nOrigin> designates the starting point from which the file pointer should he moved, as shown in the following table:

       <nOrigin>   fileio.ch     File position
       ----------- ------------- ---------------------------------- 
       0           FS_SET        Beginning of file
       1           FS_RELATIVE   Current file pointer position
       2           FS_END        End of file

If a value is not provided for <nOrigin>, it defaults to 0 and moves the file pointer from the beginning of the file.

Examples

      // here is a function that read one text line from an open file

      // nH = file handle obtained from FOpen()
      // cB = a string buffer passed-by-reference to hold the result
      // nMaxLine = maximum number of bytes to read

      FUNCTION FREADln( nH, cB, nMaxLine )
         LOCAL cLine, nSavePos, nEol, nNumRead
         cLine := Space( nMaxLine )
         cB := ""
         nSavePos := FSeek( nH, 0, FS_RELATIVE )
         nNumRead := FRead( nH, @cLine, nMaxLine )
         IF ( nEol := At( hb_eol(), SubStr( cLine, 1, nNumRead ) ) ) == 0
            cB := cLine
         ELSE
            cB := SubStr( cLine, 1, nEol - 1 )
            FSEEK( nH, nSavePos + nEol + 1, FS_SET )
         ENDIF
         RETURN nNumRead != 0

Compliance

Clipper

Files

Library is rtl Header is fileio.ch

Seealso

FCREATE(), FERROR(), FOPEN(), FREAD(), FREADSTR(), FWRITE()

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3 responses to “FSeek()

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