c#替换原有⽂件内容
//实现替换原有⽂件内容
//Seek(0, SeekOrigin.Begin)将指针指向⽂件的开始，才能从⽂件的开头，但是此时如果新写⼊的流长度⼩于原有⽂件长度，则会保留原⽂件多余的信息using (FileStream fileStream = new FileStream(file, FileMode.Open, FileAccess.Write, FileShare.Write))
{
fileStream.Seek(0, SeekOrigin.Begin);
using (StreamWriter streamWriter = new StreamWriter(fileStream))
{
streamWriter.Write("this is clear file");
fileStream.Flush();
streamWriter.Close();
}
fileStream.Close();
}
//调⽤Stream的SetLength这个⽅法，将长度设为0，可以实现清空原有⽂件
using (FileStream fileStream = new FileStream(file, FileMode.Open, FileAccess.Write, FileShare.Write))
{
fileStream.SetLength(0);
using (StreamWriter streamWriter = new StreamWriter(fileStream))
{
streamWriter.Write("this is clear file");
fileStream.Flush();
streamWriter.Close();
}
fileStream.Close();
}truncated file
//如果⽂件已存在则清空，从Truncate打开的⽂件中读取将引发异常
using (FileStream fileStream = new FileStream(file, FileMode.Truncate, FileAccess.Write, FileShare.Write))
{
using (StreamWriter streamWriter = new StreamWriter(fileStream))
{
streamWriter.Write("this is");
fileStream.Flush();
streamWriter.Close();
}
fileStream.Close();
}

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