Question

我在C＃代码中使用string.split（）来读取制表符分隔文件。我正面临着代码示例中提到的“OutOfMemory异常”。

在这里，我想知道为什么文件大小为16 MB会出现问题？

这是正确的方法吗？

using (StreamReader reader = new StreamReader(_path))
{
  //...........Load the first line of the file................
  string headerLine = reader.ReadLine();

  MeterDataIPValueList objMeterDataList = new MeterDataIPValueList();
  string[] seperator = new string[1];   //used to sepreate lines of file

  seperator[0] = "\r\n";
  //.............Load Records of file into string array and remove all empty lines of file.................
  string[] line = reader.ReadToEnd().Split(seperator, StringSplitOptions.RemoveEmptyEntries);
  int noOfLines = line.Count();
  if (noOfLines == 0)
  {
    mFileValidationErrors.Append(ConstMsgStrings.headerOnly + Environment.NewLine);
  }
  //...............If file contains records also with header line..............
  else
  {
    string[] headers = headerLine.Split('\t');
    int noOfColumns = headers.Count();

    //.........Create table structure.............
    objValidateRecordsTable.Columns.Add("SerialNo");
    objValidateRecordsTable.Columns.Add("SurveyDate");
    objValidateRecordsTable.Columns.Add("Interval");
    objValidateRecordsTable.Columns.Add("Status");
    objValidateRecordsTable.Columns.Add("Consumption");

    //........Fill objValidateRecordsTable table by string array contents ............

    int recordNumber;  // used for log
    #region ..............Fill objValidateRecordsTable.....................
    seperator[0] = "\t";
    for (int lineNo = 0; lineNo < noOfLines; lineNo++)
    {
      recordNumber = lineNo + 1;
      **string[] recordFields = line[lineNo].Split(seperator, StringSplitOptions.RemoveEmptyEntries);** // Showing me error when we  split columns
      if (recordFields.Count() == noOfColumns)
      {
        //Do processing
      }

Answer 1

Split的实现很差，并且在应用于大字符串时会出现严重的性能问题。请参阅this article for details on memory requirements by split function：

当您对包含1355049个逗号分隔的字符串的字符串进行拆分时会发生什么情况，每个字符串包含16个字符，总字符长度为25745930？



指向字符串对象的指针数组：连续虚拟地址空间为4（地址指针）* 1355049 = 5420196（数组大小）+ 16（用于簿记）= 5420212.



1355049个字符串的非连续虚拟地址空间，每个字符串54个字节。这并不意味着所有这130万个字符串都会分散在整个堆中，但它们不会在LOH上分配。 GC将在Gen0堆上的串上分配它们。



Split.Function将创建大小为25745930的System.Int32 []的内部数组，消耗（102983736字节）~98MB的LOH，这是非常昂贵的L.

Answer 2

首先尝试不将整个文件读入数组“reader.ReadToEnd（）”直接逐行读取文件..

  using (StreamReader sr = new StreamReader(this._path))
        {
            string line = "";
            while(( line= sr.ReadLine()) != null)
            {
                string[] cells = line.Split(new string[] { "\t" }, StringSplitOptions.None);
                if (cells.Length > 0)
                {

                }
            }
        }

Answer 3

如果可以的话，我建议逐行阅读，但有时不按新行划分。

因此，您可以随时编写自己的内存效率分割。这解决了我的问题。

    private static IEnumerable<string> CustomSplit(string newtext, char splitChar)
    {
        var result = new List<string>();
        var sb = new StringBuilder();
        foreach (var c in newtext)
        {
            if (c == splitChar)
            {
                if (sb.Length > 0)
                {
                    result.Add(sb.ToString());
                    sb.Clear();
                }
                continue;
            }
            sb.Append(c);
        }
        if (sb.Length > 0)
        {
            result.Add(sb.ToString());
        }
        return result;
    }

Answer 4

我用自己的。它已通过10次单元测试进行了测试..

public static class StringExtensions
{

    // the string.Split() method from .NET tend to run out of memory on 80 Mb strings. 
    // this has been reported several places online. 
    // This version is fast and memory efficient and return no empty lines. 
    public static List<string> LowMemSplit(this string s, string seperator)
    {
        List<string> list = new List<string>();
        int lastPos = 0;
        int pos = s.IndexOf(seperator);
        while (pos > -1)
        {
            while(pos == lastPos)
            {
                lastPos += seperator.Length;
                pos = s.IndexOf(seperator, lastPos);
                if (pos == -1)
                    return list;
            }

            string tmp = s.Substring(lastPos, pos - lastPos);
            if(tmp.Trim().Length > 0)
                list.Add(tmp);
            lastPos = pos + seperator.Length;
            pos = s.IndexOf(seperator, lastPos);
        }

        if (lastPos < s.Length)
        {
            string tmp = s.Substring(lastPos, s.Length - lastPos);
            if (tmp.Trim().Length > 0)
                list.Add(tmp);
        }

        return list;
    }
}

Answer 5

尝试按行读取文件，而不是拆分整个内容。

string.split（）读取制表符分隔文件时出现“内存不足异常”

5 个答案: