在 vb.net 中读取非常大的文本文件时出现内存不足错误

Question

我的任务是处理一个 3.2GB 的定宽分隔文本文件。每行有 1563 个字符长，文本文件中大约有 210 万行。在阅读了大约 100 万行之后，我的程序因内存不足异常错误而崩溃。

Imports System.IO
Imports Microsoft.VisualBasic.FileIO

Module TestFileCount
    ''' <summary>
    ''' Gets the total number of lines in a text file by reading a line at a time
    ''' </summary>
    ''' <remarks>Crashes when count reaches 1018890</remarks>
    Sub Main()
        Dim inputfile As String = "C:\Split\BIGFILE.txt"
        Dim count As Int32 = 0
        Dim lineoftext As String = ""

        If File.Exists(inputfile) Then
            Dim _read As New StreamReader(inputfile)
            Try
                While (_read.Peek <> -1)
                    lineoftext = _read.ReadLine()
                    count += 1
                End While

                Console.WriteLine("Total Lines in " & inputfile & ": " & count)
            Catch ex As Exception
                Console.WriteLine(ex.Message)
            Finally
                _read.Close()
            End Try
        End If
    End Sub
End Module

这是一个非常简单的程序，一次读取一行文本文件，所以我认为它不应该在缓冲区中占用太多内存。

对于我的生活，我无法弄清楚它为什么会崩溃。这里有人有什么想法吗？

Answer 1

我不知道这是否能解决您的问题，但不要使用 peek，将您的循环更改为：（这是 C#，但您应该能够将其转换为 VB）

while (_read.ReadLine() != null)
{
    count += 1
}

如果您需要在循环中使用文本行而不是仅计算行数，只需将代码修改为

while ((lineoftext = _read.ReadLine()) != null)
{
    count += 1
    //Do something with lineoftext
}

---

有点离题和作弊，如果每行真的是 1563 个字符长（包括行尾）并且文件是纯 ASCII（所以所有字符占用一个字节）你可以这样做（再次 C# 但是你应该会翻译）

long bytesPerLine = 1563;
string inputfile = @"C:\Split\BIGFILE.txt"; //The @ symbol is so we don't have to escape the `\`
long length;

using(FileStream stream = File.Open(inputFile, FileMode.Open)) //This is the C# equivilant of the try/finally to close the stream when done.
{
    length = stream.Length;
}

Console.WriteLine("Total Lines in {0}: {1}", inputfile, (length / bytesPerLine ));

Answer 2

尝试使用ReadAsync，或者你可以使用DiscardBufferedData（但是这个慢）

Dim inputfile As String = "C:\Example\existingfile.txt" 
    Dim result() As String 
    Dim builder As StringBuilder = New StringBuilder()

    Try
        Using reader As StreamReader = File.OpenText(inputfile)
            ReDim result(reader.BaseStream.Length)
            Await reader.ReadAsync(result, 0, reader.BaseStream.Length)
        End Using 

        For Each str As String In result
            builder.Append(str)         
        Next
      Dim count as Integer=builder.Count()
       Console.WriteLine("Total Lines in " & inputfile & ": " & count)
    Catch ex As Exception
            Console.WriteLine(ex.Message)
    End Try