我正在閱讀 csv 文件：string line;StreamReader sr = new StreamReader(file.ToString());while ((line = sr.ReadLine()) != null){ string col1 = line.Split(',')[10]; //old value col1 = "my value"; //new value}sr.Close();sr.Dispose();我想用新值替換舊值。然后我需要保存更改后的文件。我怎樣才能做到這一點？
2 回答
胡說叔叔
TA貢獻1804條經驗 獲得超8個贊
我建議使用File類而不是Streams 和Readers。Linq在查詢數據的時候非常方便：
var modifiedData = File
.ReadLines(file.ToString())
.Select(line => line.Split(','))
.Select(items => {
//TODO: put relevant logic here: given items we should return csv line
items[10] = "my value";
return string.Join(",", items);
})
.ToList(); // <- we have to store modified data in memory
File.WriteAllLines(file.ToString(), modifiedData);
另一種可能性（例如，當初始文件太長而無法容納內存時）是將修改后的數據保存到一個臨時文件中，然后Move：
var modifiedData = File
.ReadLines(file.ToString())
.Select(line => line.Split(','))
.Select(items => {
//TODO: put relevant logic here: given items we should return csv line
items[10] = "my value";
return string.Join(",", items);
});
string tempFile = Path.Combine(Path.GetTempPath(), $"{Guid.NewGuid()}.tmp");
File.WriteAllLines(tempFile, modifiedData);
File.Delete(file.ToString());
File.Move(tempFile, file.ToString());
慕斯709654
TA貢獻1840條經驗 獲得超5個贊
一次讀取整個文件會占用大量內存。更不用說創建它的平行副本了。使用流可以修復它。嘗試這個：
void Modify()
{
using (var fs = new FileStream(file, FileMode.Open, FileAccess.ReadWrite))
{
string line;
long position;
while ((line = fs.ReadLine(out position)) != null)
{
var tmp = line.Split(',');
tmp[1] = "00"; // new value
var newLine = string.Join(",", tmp);
fs.WriteLine(position, newLine);
}
}
}
擴展名：
static class FileStreamExtensions
{
private static readonly char[] newLine = Environment.NewLine.ToCharArray();
private static readonly int length = Environment.NewLine.Length;
private static readonly char eof = '\uFFFF';
public static string ReadLine(this FileStream fs, out long position)
{
position = fs.Position;
var chars = new List<char>();
char c;
while ((c = (char)fs.ReadByte()) != eof && (chars.Count < length || !chars.Skip(chars.Count - 2).SequenceEqual(newLine)))
{
chars.Add(c);
}
fs.Position--;
if (chars.Count == 0)
return null;
return new string(chars.ToArray());
}
public static void WriteLine(this FileStream fs, long position, string line)
{
var bytes = line.ToCharArray().Concat(newLine).Select(c => (byte)c).ToArray();
fs.Position = position;
fs.Write(bytes, 0, bytes.Length);
}
}
缺點是您必須保持值的長度相同。例如999和__9的長度都是 3。解決這個問題會使事情變得更加復雜，所以我會這樣處理。
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