try
{
    // Bucket name in the format of bucketname-APPID. You can get APPID by referring to https://console.tencentcloud.com/developer.
    string bucket = "examplebucket-1250000000";
    string key = "exampleobject"; // Object key

    SelectObjectRequest request = new SelectObjectRequest(bucket, key);

    ObjectSelectionFormat.JSONFormat jSONFormat = new ObjectSelectionFormat.JSONFormat();
    jSONFormat.Type = "DOCUMENT";
    jSONFormat.RecordDelimiter = "\\n";

    string outputFile = "select_local_file.json";

    request.SetExpression("Select * from COSObject")
            .SetInputFormat(new ObjectSelectionFormat(null, jSONFormat))
            .SetOutputFormat(new ObjectSelectionFormat(null, jSONFormat))
            .SetCosProgressCallback(delegate (long progress, long total) {
                Console.WriteLine("OnProgress : " + progress + "," + total);
            })
            .OutputToFile(outputFile)
            ;

    SelectObjectResult selectObjectResult =  cosXml.SelectObject(request);
    Console.WriteLine(selectObjectResult.stat);
}
catch (COSXML.CosException.CosClientException clientEx)
{
    Console.WriteLine("CosClientException: " + clientEx.StackTrace);
    Console.WriteLine("CosClientException: " + clientEx.Message);
}
catch (COSXML.CosException.CosServerException serverEx)
{
    Console.WriteLine("CosServerException: " + serverEx.GetInfo());
}