FUNCTIONUnder review

FSeek

FSeek( nHandle, nOffSet, [nOrigem] ) --> nRet

Positions a file pointer in bytes.

FSeekAdvPL

01 · OVERVIEW

Overview

FSeek moves relative to FS_SET, FS_RELATIVE or FS_END and returns an absolute zero-based position. Seeking zero bytes from the end obtains size while changing the cursor. The community example uses this technique then returns to the start; the adaptation opens read-only, checks FError before continuing and closes its handle. File bytes are not characters and file position is not table RecNo. (TOTVS, n.d., ref. 1)

02 · SYNTAX

Syntax

FSeek( nHandle, nOffSet, [nOrigem] ) --> nRet

Parameters

nHandle

NumericRequired

Valid handle from FOpen/FCreate; zero is valid too.

nOffSet

NumericRequired

Byte offset.

nOrigem

NumericOptional

FS_SET=0, FS_RELATIVE=1, FS_END=2; start by default.

Return value

New absolute byte position from the start.

03 · PRACTICAL EXAMPLE

Commented example

#Include "Protheus.ch"
#Include "Fileio.ch"

User Function Ed396()
    Local nHandle := -1
    Local nError := 0
    Local nSize
    // Pre-existing fictional file in the test context; shared reading.
    nHandle := FOpen("editorial-test.txt", FO_READ + FO_SHARED)
    If nHandle < 0
        nError := FError()
        ConOut(cValToChar(nError))
    Else
        nSize := FSeek(nHandle, 0, FS_END)
        nError := FError()
        If nError == 0
            ConOut(cValToChar(nSize))
            // Reposition before any later read.
            FSeek(nHandle, 0, FS_SET)
        Else
            ConOut(cValToChar(nError))
        EndIf
        If !FClose(nHandle)
            ConOut(cValToChar(FError()))
        EndIf
    EndIf
Return Nil

Expected result

Test-file byte size or diagnostic; no fixed value assumed. Under review: editorial example neither compiled nor run in Protheus. Check includes, release, RDD and context before testing.

BEST PRACTICES

Check path, permissions, platform and handle ownership. Close only handles obtained by this routine, including complete-application error handling.
Under review: editorial example neither compiled nor run in Protheus. Check includes, release, RDD and context before testing.