在实际开发过中,发现如果多个程序去读写一个文件时,会发生一些错误,现在在读写文件之前,判断文件是否已经被子其它程序正在使用.-In the actual development have been found if the number of procedures to read and write a file, some mistakes will happen, and now in reading and writing paper, to determine whether docum