To use libssh, you need to install it on your system and link it with your C++ code during the compilation process. Here's an example of how you can use libssh to perform an SFTP file transfer from one server to another:

#include <iostream>
#include <libssh/libssh.h>
#include <libssh/sftp.h>

int main() {
    ssh_session sshSession;
    sftp_session sftpSession;

    // Create a new SSH session and set options
    sshSession = ssh_new();
    if (sshSession == nullptr) {
        std::cerr << "Error creating SSH session." << std::endl;
        return 1;
    }

    // Set SSH options (hostname, port, etc.)
    // ssh_options_set(sshSession, SSH_OPTIONS_HOST, "your_hostname");
    // ssh_options_set(sshSession, SSH_OPTIONS_PORT, port_number);
    // ...

    // Connect to the SSH server
    if (ssh_connect(sshSession) != SSH_OK) {
        std::cerr << "Error connecting to SSH server: " << ssh_get_error(sshSession) << std::endl;
        ssh_free(sshSession);
        return 1;
    }

    // Authenticate with the SSH server using username and password, or key-based authentication
    // ssh_userauth_password(sshSession, nullptr, "password");
    // ssh_userauth_publickey_auto(sshSession, nullptr, nullptr);

    // Start the SFTP subsystem
    sftpSession = sftp_new(sshSession);
    if (sftpSession == nullptr) {
        std::cerr << "Error creating SFTP session: " << ssh_get_error(sshSession) << std::endl;
        ssh_disconnect(sshSession);
        ssh_free(sshSession);
        return 1;
    }

    // Initialize the SFTP session
    if (sftp_init(sftpSession) != SSH_OK) {
        std::cerr << "Error initializing SFTP session: " << ssh_get_error(sshSession) << std::endl;
        sftp_free(sftpSession);
        ssh_disconnect(sshSession);
        ssh_free(sshSession);
        return 1;
    }

    // Open the source file for reading
    sftp_file fileSource = sftp_open(sftpSession, "path_to_source_file", O_RDONLY, 0);
    if (fileSource == nullptr) {
        std::cerr << "Error opening source file: " << ssh_get_error(sshSession) << std::endl;
        sftp_free(sftpSession);
        ssh_disconnect(sshSession);
        ssh_free(sshSession);
        return 1;
    }

    // Create the destination file on the remote server
    sftp_file fileDestination = sftp_open(sftpSession, "path_to_destination_file", O_CREAT | O_WRONLY, S_IRWXU);
    if (fileDestination == nullptr) {
        std::cerr << "Error creating destination file: " << ssh_get_error(sshSession) << std::endl;
        sftp_close(fileSource);
        sftp_free(sftpSession);
        ssh_disconnect(sshSession);
        ssh_free(sshSession);
        return 1;
    }

    // Transfer the file from source to destination
    const int bufferSize = 4096;
    char buffer[bufferSize];
    int bytesRead;
    while ((bytesRead = sftp_read(fileSource, buffer, bufferSize)) > 0) {
        sftp_write(fileDestination, buffer, bytesRead);
    }

    // Close the file handles
    sftp_close(fileSource);
    sftp_close(fileDestination);

    // Cleanup and disconnect
    sftp_free(sftpSession);
    ssh_disconnect(sshSession);
    ssh_free(sshSession);

    std::cout << "File transfer complete." << std::endl;
    return 0;
}


using system command file:
In this example, the sourceFile variable represents the file you want to transfer, and the destinationFile variable represents the remote server and destination path for the file.

The sftpCommand string is constructed to execute the SFTP command using the system function. It opens an SFTP session, uploads the file using the put command, and then terminates the session with bye.

Please note that this method relies on the availability of the sftp command on your system, and it might not work if the command is not installed or accessible. Additionally, make sure to adjust the file paths and the remote server address to match your specific setup.

Remember to handle any error cases and validate the success of the transfer based on the exit status returned by the system function.

#include <cstdlib>
#include <iostream>

int main() {
    std::string sourceFile = "/path/to/source/file";
    std::string destinationFile = "user@remotehost:/path/to/destination/file";

    std::string sftpCommand = "sftp " + destinationFile + " <<EOF\n"
                              "put " + sourceFile + "\n"
                              "bye\n"
                              "EOF";

    int exitStatus = system(sftpCommand.c_str());

    if (exitStatus == 0) {
        std::cout << "File transfer complete." << std::endl;
    } else {
        std::cerr << "File transfer failed." << std::endl;
    }

    return 0;
}