Xbase++

Write Text at a 32-bit Offset in a Remote SFTP File

Demonstrates the Chilkat SFtp.WriteFileText32 method, which encodes text and writes it at a specific 32-bit byte offset in an open handle. The arguments are the handle, the offset, the charset, and the text.

Background: Explicit-offset writes enable random access — patching a fixed-length record in place, for instance, without rewriting the whole file. The offset is a byte position, not a character position, so with a variable-width encoding like UTF-8 you must account for the encoded size of preceding characters to land where you intend. After the write, the sequential position continues just past the bytes written.

Chilkat Xbase++ Downloads

Download Chilkat for Xbase++

Xbase++

LOCAL nSuccess
LOCAL oSftp
LOCAL nPort
LOCAL cPassword
LOCAL cHandle
LOCAL nOffset

nSuccess := 0

//  Demonstrates the SFtp.WriteFileText32 method, which encodes text and writes it at a specific
//  32-bit byte offset in an open handle.  The 1st argument is the handle, the 2nd is the offset,
//  the 3rd is the charset, and the 4th is the text.

oSftp := CreateObject("Chilkat.SFtp")

//  Connect, authenticate, and initialize the SFTP subsystem.
nPort := 22
nSuccess := oSftp:Connect("sftp.example.com", nPort)
IF (nSuccess == 0)
    ? oSftp:LastErrorText
    oSftp:destroy()
    RETURN
ENDIF

//  Normally you would not hard-code the password in source.  You should instead obtain it
//  from an interactive prompt, environment variable, or a secrets vault.
cPassword := "mySshPassword"

nSuccess := oSftp:AuthenticatePw("mySshLogin", cPassword)
IF (nSuccess == 0)
    ? oSftp:LastErrorText
    oSftp:destroy()
    RETURN
ENDIF

nSuccess := oSftp:InitializeSftp()
IF (nSuccess == 0)
    ? oSftp:LastErrorText
    oSftp:destroy()
    RETURN
ENDIF

//  Open the remote file for read/write so an existing file can be modified in place.
cHandle := oSftp:OpenFile("subdir/record.dat", "readWrite", "openOrCreate")
IF (oSftp:LastMethodSuccess == 0)
    ? oSftp:LastErrorText
    oSftp:destroy()
    RETURN
ENDIF

//  Overwrite 5 bytes starting at offset 10.  The offset is a byte position, not a character
//  position, so it must account for the encoded size of any multibyte characters.
nOffset := 10
nSuccess := oSftp:WriteFileText32(cHandle, nOffset, "utf-8", "HELLO")
IF (nSuccess == 0)
    ? oSftp:LastErrorText
    oSftp:destroy()
    RETURN
ENDIF

nSuccess := oSftp:CloseHandle(cHandle)
IF (nSuccess == 0)
    ? oSftp:LastErrorText
    oSftp:destroy()
    RETURN
ENDIF

? "Wrote at the specified offset."

oSftp:Disconnect()

oSftp:destroy()