FileStream fs;
StreamWriter sw;
string strContent;
string strDir = @"D:\ST";
string strPath;

strPath = strDir + @"\S1.txt";    // S1.txt文件全路径
fs = new FileStream(strPath, FileMode.OpenOrCreate);
sw = new StreamWriter(fs, Encoding.Default);
strContent = WriteToS1();         // 生成S1文件的内容
sw.Write(strContent);
            
strPath = strDir + @"S2.txt";    // S2.txt文件全路径
fs = new FileStream(strPath, FileMode.OpenOrCreate);
sw = new StreamWriter(fs, Encoding.Default);
strContent = WriteToS2();        // 生成S2文件的内容
sw.Write(strContent);

sw.Close();