Unicode C

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.

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Unicode C

#include <C_CkSFtpW.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkSFtpW sftp;
    int port;
    const wchar_t *password;
    const wchar_t *handle;
    int offset;

    success = FALSE;

    //  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.

    sftp = CkSFtpW_Create();

    //  Connect, authenticate, and initialize the SFTP subsystem.
    port = 22;
    success = CkSFtpW_Connect(sftp,L"sftp.example.com",port);
    if (success == FALSE) {
        wprintf(L"%s\n",CkSFtpW_lastErrorText(sftp));
        CkSFtpW_Dispose(sftp);
        return;
    }

    //  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.
    password = L"mySshPassword";

    success = CkSFtpW_AuthenticatePw(sftp,L"mySshLogin",password);
    if (success == FALSE) {
        wprintf(L"%s\n",CkSFtpW_lastErrorText(sftp));
        CkSFtpW_Dispose(sftp);
        return;
    }

    success = CkSFtpW_InitializeSftp(sftp);
    if (success == FALSE) {
        wprintf(L"%s\n",CkSFtpW_lastErrorText(sftp));
        CkSFtpW_Dispose(sftp);
        return;
    }

    //  Open the remote file for read/write so an existing file can be modified in place.
    handle = CkSFtpW_openFile(sftp,L"subdir/record.dat",L"readWrite",L"openOrCreate");
    if (CkSFtpW_getLastMethodSuccess(sftp) == FALSE) {
        wprintf(L"%s\n",CkSFtpW_lastErrorText(sftp));
        CkSFtpW_Dispose(sftp);
        return;
    }

    //  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.
    offset = 10;
    success = CkSFtpW_WriteFileText32(sftp,handle,offset,L"utf-8",L"HELLO");
    if (success == FALSE) {
        wprintf(L"%s\n",CkSFtpW_lastErrorText(sftp));
        CkSFtpW_Dispose(sftp);
        return;
    }

    success = CkSFtpW_CloseHandle(sftp,handle);
    if (success == FALSE) {
        wprintf(L"%s\n",CkSFtpW_lastErrorText(sftp));
        CkSFtpW_Dispose(sftp);
        return;
    }

    wprintf(L"Wrote at the specified offset.\n");

    CkSFtpW_Disconnect(sftp);


    CkSFtpW_Dispose(sftp);

    }