C++

Read Text at a 32-bit Offset from a Remote SFTP File

Demonstrates the Chilkat SFtp.ReadFileText32 method, which reads up to a number of bytes from a specific 32-bit byte offset of an open handle and decodes them to text. The arguments are the handle, the offset, the maximum number of bytes, and the charset.

Background: Reading from an explicit offset lets you fetch just the part of a file you need — a header, a record at a known position, a slice of a large log — without downloading everything before it. As with offset writes, the offset counts bytes rather than characters, so it must respect the encoded width of any multibyte content.

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#include <CkSFtp.h>

void ChilkatSample(void)
    {
    bool success = false;

    //  Demonstrates the SFtp.ReadFileText32 method, which reads up to a number of bytes from a
    //  specific 32-bit byte offset of an open handle and decodes them to text.  The 1st argument is
    //  the handle, the 2nd is the offset, the 3rd is the maximum number of bytes, and the 4th is the
    //  charset.

    CkSFtp sftp;

    //  Connect, authenticate, and initialize the SFTP subsystem.
    int port = 22;
    success = sftp.Connect("sftp.example.com",port);
    if (success == false) {
        std::cout << sftp.lastErrorText() << "\r\n";
        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.
    const char *password = "mySshPassword";

    success = sftp.AuthenticatePw("mySshLogin",password);
    if (success == false) {
        std::cout << sftp.lastErrorText() << "\r\n";
        return;
    }

    success = sftp.InitializeSftp();
    if (success == false) {
        std::cout << sftp.lastErrorText() << "\r\n";
        return;
    }

    const char *handle = sftp.openFile("subdir/record.dat","readOnly","openExisting");
    if (sftp.get_LastMethodSuccess() == false) {
        std::cout << sftp.lastErrorText() << "\r\n";
        return;
    }

    //  Read 5 bytes starting at byte offset 10, without first reading the bytes before it.
    int offset = 10;
    int numBytes = 5;
    const char *text = sftp.readFileText32(handle,offset,numBytes,"utf-8");
    if (sftp.get_LastMethodSuccess() == false) {
        std::cout << sftp.lastErrorText() << "\r\n";
        return;
    }

    std::cout << text << "\r\n";

    success = sftp.CloseHandle(handle);
    if (success == false) {
        std::cout << sftp.lastErrorText() << "\r\n";
        return;
    }

    sftp.Disconnect();
    }