C＃将文件拆分为两个字节数组

Question

Because the maximum value of a byte array is 2GB, lets say i have a larger file and i need to convert it to a byte array. Since i can't hold the whole file, how should i convert it into two?

I tried:

long length = new System.IO.FileInfo(@"c:\a.mp4").Length;
int chunkSize = Convert.ToInt32(length / 2); 


byte[] part2;
FileStream fileStream = new FileStream(filepath, FileMode.Open, FileAccess.Read);
try
{
    part2 = new byte[chunkSize];            // create buffer
    fileStream.Read(part2, 0, chunkSize);
}
finally
{
    fileStream.Close();
}

byte[] part3;
fileStream = new FileStream(filepath, FileMode.Open, FileAccess.Read);
try
{
    part3 = new byte[chunkSize];            // create buffer
    fileStream.Read(part3, 5, (int)(length - (long)chunkSize));
}
finally
{
    fileStream.Close();
}

but it's not working.

Any ideas?

Answer 1

You can use a StreamReader to read in file too large to read into a byte array

const int max = 1024*1024;

public void ReadALargeFile(string file, int start = 0)
{
    FileStream fileStream = new FileStream(file, FileMode.Open,FileAccess.Read);
    using (fileStream)
    {
        byte[] buffer = new byte[max];
        fileStream.Seek(start, SeekOrigin.Begin);
        int bytesRead = fileStream.Read(buffer, start, max);
        while(bytesRead > 0)
        {
            DoSomething(buffer, bytesRead);
            bytesRead = fileStream.Read(buffer, start, max);
        }
    }
}

Answer 2

If you are working with extremely large files, you should use MemoryMappedFile , which maps a physical file to a memory space:

using (var mmf = MemoryMappedFile.CreateFromFile(@"c:\path\to\big.file"))
{
    using (var accessor = mmf.CreateViewAccessor())
    {
        byte myValue = accessor.ReadByte(someOffset);
        accessor.Write((byte)someValue);
    }
}

See also: MemoryMappedViewAccessor

You can also read/write chunks of the file with the different methods in MemoryMappedViewAccessor .

Answer 3

This was my solution:

byte[] part1;
byte[] part2;
bool odd = false;
int chunkSize = Convert.ToInt32(length/2);


if (length % 2 == 0)
{
    part1 = new byte[chunkSize];
    part2 = new byte[chunkSize];
}
else
{
    part1 = new byte[chunkSize];
    part2 = new byte[chunkSize + 1];
    odd = true;
}

FileStream fileStream = new FileStream(filepath, FileMode.Open, FileAccess.Read);
using (fileStream)
{
    fileStream.Seek(0, SeekOrigin.Begin);
    int bytesRead = fileStream.Read(part1, 0, chunkSize);
    if (odd)
    {
        bytesRead = fileStream.Read(part2, 0, chunkSize + 1);
    }
    else
    {
        bytesRead = fileStream.Read(part2, 0, chunkSize);
    }
}